What/how does compression ratio affect an engine?

[[email protected]]

Hi,

So I was fantasizing the other day (as I do quite a bit) about my
latest dream-plane-to-build: an RV-9A. (Note that this is fantasy in
the extreme as I'm not a pilot yet AND I have no money!)

I was thinking of how to power this plane. A Jet-A burning diesel
would be great but that's another story. I spotted an ad for
Superior's XP-series engines in Kitplanes. The website has a great
"build your own engine" feature where you get to change all the bits
and customize the engine.

One of the things you have to choose is compression ratio: 7:1
(150hp), 8.5:1 (160hp), or 9:1 (165hp).
Going for the 7:1 option (from the default 8.5:1) adds $100 to the
price! I'm assuming this is a supply/demand issue.

So my question (finally) is: what is the effect of a higher or lower
compression ratio? I believe TBO for all three engines is still 2000
hours.

- Is there a difference in wear?
- Would maximum power be produced at the same RPM for all three
engines? In other words is there a relationship like (power) =
(compression ratio) x (RPM) such that these engines all operate at the
same RPM? In which case wear would be the same...(?)

For the RV-9A 150hp would be fine. I guess I'm trying to understand
what benefit is to be had by spending the extra $100 to go for the
lower compression pistons. All in my fantasy :)

Thanks,

Michael

[Scott[_1_]]

Well, one thing I know, is that with the lower compression ratio (ie 7:1
for the 150HP) is that the engine can run on auto fuel. That's why I'm
planning on a 150 HP in my RV-4. The higher compression engines take 100LL.

Scott
http://corbenflyer.tripod.com/
Gotta Fly or Gonna Die
Building RV-4 (Super Slow Build Version)

wrote:
> Hi,
>
> So I was fantasizing the other day (as I do quite a bit) about my
> latest dream-plane-to-build: an RV-9A. (Note that this is fantasy in
> the extreme as I'm not a pilot yet AND I have no money!)
>
> I was thinking of how to power this plane. A Jet-A burning diesel
> would be great but that's another story. I spotted an ad for
> Superior's XP-series engines in Kitplanes. The website has a great
> "build your own engine" feature where you get to change all the bits
> and customize the engine.
>
> One of the things you have to choose is compression ratio: 7:1
> (150hp), 8.5:1 (160hp), or 9:1 (165hp).
> Going for the 7:1 option (from the default 8.5:1) adds $100 to the
> price! I'm assuming this is a supply/demand issue.
>
> So my question (finally) is: what is the effect of a higher or lower
> compression ratio? I believe TBO for all three engines is still 2000
> hours.
>
> - Is there a difference in wear?
> - Would maximum power be produced at the same RPM for all three
> engines? In other words is there a relationship like (power) =
> (compression ratio) x (RPM) such that these engines all operate at the
> same RPM? In which case wear would be the same...(?)
>
> For the RV-9A 150hp would be fine. I guess I'm trying to understand
> what benefit is to be had by spending the extra $100 to go for the
> lower compression pistons. All in my fantasy :)
>
> Thanks,
>
> Michael
>
>
>

--

[Kyle Boatright]

> wrote in message
...
> Hi,
>
> So I was fantasizing the other day (as I do quite a bit) about my
> latest dream-plane-to-build: an RV-9A. (Note that this is fantasy in
> the extreme as I'm not a pilot yet AND I have no money!)
>
> I was thinking of how to power this plane. A Jet-A burning diesel
> would be great but that's another story. I spotted an ad for
> Superior's XP-series engines in Kitplanes. The website has a great
> "build your own engine" feature where you get to change all the bits
> and customize the engine.
>
> One of the things you have to choose is compression ratio: 7:1
> (150hp), 8.5:1 (160hp), or 9:1 (165hp).
> Going for the 7:1 option (from the default 8.5:1) adds $100 to the
> price! I'm assuming this is a supply/demand issue.
>
> So my question (finally) is: what is the effect of a higher or lower
> compression ratio? I believe TBO for all three engines is still 2000
> hours.
>
> - Is there a difference in wear?
> - Would maximum power be produced at the same RPM for all three
> engines? In other words is there a relationship like (power) =
> (compression ratio) x (RPM) such that these engines all operate at the
> same RPM? In which case wear would be the same...(?)
>
> For the RV-9A 150hp would be fine. I guess I'm trying to understand
> what benefit is to be had by spending the extra $100 to go for the
> lower compression pistons. All in my fantasy :)
>
> Thanks,
>
> Michael

The extra $100 is probably because the 7:1 pistons are a special order item,
as opposed to the 8.5:1 pistons which are the standard.

Max RPM is the same for all 3 engines, and the only wear difference should
be on the connecting rods. Apparently the difference isn't enough to change
the TBO, which is a theoretical figure anyway.

As to autogas vs 100LL, plenty of people running 8.5:1 compression engines
are running autofuel. A bigger issue with autofuel (at least in engines
with a compression rapto of 8.5:1 or less) is vapor lock, rather than
detonation.

Kyle Boatright
160hp (8.5:1 Lycoming) RV-6

[[email protected]]

OK, not cool to reply to my own post, I know. But I just found this
great resource which basically answers all my questions:

http://www.lycoming.textron.com/support/tips-advice/key-reprints/

"Lycoming provides helpful information in various publications,
including Lycoming Flyer Key Reprints. Lycoming's Key
Reprints is our effort to continually share our best practices,
key lessons and engines systems knowledge to empower
our customers."

Lower compression => lower chance of preignition => lower octane
required (ie. auto fuel)!
Yes, that would make a difference to the pocket book!

The issue of using auto fuel is addressed in this series also:

"Auto fuel is now being used as a substitute for Grade 80
aviation gasoline under STCs issued by the FAA. Most
major oil companies and engine manufacturers continue
to recommend that aircraft piston engines be operated
only on aviation gasoline. Deterioration of engine and fuel
system parts have been reported in aircraft using auto
fuel. Operators should consider the added risk of using
auto fuel in aircraft. Remember -- a pilot can't pull over
to the side of the road when fuel creates a problem with
the engine."

[Scott[_1_]]

One thing I think "might" be a concern is that burning 100LL (can't get
80 octane avgas these days) in an engine built for 80 octane is the
extra heat. I think valves are most likely to be affected by burning
the 100LL instead of 80. Might be all wet on this, but that's what I've
heard and I'm NOT an engine mechanic...just a user :) You might try
digging in the Lycoming site and see what they say about 80 vs 100LL...

Scott


wrote:
> OK, not cool to reply to my own post, I know. But I just found this
> great resource which basically answers all my questions:
>
> http://www.lycoming.textron.com/support/tips-advice/key-reprints/
>
> "Lycoming provides helpful information in various publications,
> including Lycoming Flyer Key Reprints. Lycoming's Key
> Reprints is our effort to continually share our best practices,
> key lessons and engines systems knowledge to empower
> our customers."
>
> Lower compression => lower chance of preignition => lower octane
> required (ie. auto fuel)!
> Yes, that would make a difference to the pocket book!
>
> The issue of using auto fuel is addressed in this series also:
>
> "Auto fuel is now being used as a substitute for Grade 80
> aviation gasoline under STCs issued by the FAA. Most
> major oil companies and engine manufacturers continue
> to recommend that aircraft piston engines be operated
> only on aviation gasoline. Deterioration of engine and fuel
> system parts have been reported in aircraft using auto
> fuel. Operators should consider the added risk of using
> auto fuel in aircraft. Remember -- a pilot can't pull over
> to the side of the road when fuel creates a problem with
> the engine."
>
>

--
Scott
http://corbenflyer.tripod.com/
Gotta Fly or Gonna Die
Building RV-4 (Super Slow Build Version)

[Bob Fry]

>>>>> "Scott" == Scott > writes:

Scott> One thing I think "might" be a concern is that burning
Scott> 100LL (can't get 80 octane avgas these days) in an engine
Scott> built for 80 octane is the extra heat.

Eh? Where's this "extra heat" come from? There is no practical unit
energy difference between different octane fuels.
--
"You, Mr. Wilkes, will die either of the pox or on the gallows."
-The Earl of Sandwich

[GeorgeB]

On Mon, 10 Dec 2007 09:23:52 -0800, Richard Riley
> wrote:

>If you're flying a homebuilt you can burn whatever you want - but the
>alcohol restriction wasn't put there at random, it increases vapor
>lock problems dramatically,

How do the planes which do fly on ethanol handle that problem,
pressurized tanks?

>and is incompatable with many of the
>materials commonly used in aircraft fuel systems.

The sealant sloshed in the tanks is one, I think ...

Do automobiles with flex-fuel capability do anything to minimize the
vapor lock issues? I'm sure the materials were selected to be ok.

[[email protected]]

On Dec 10, 11:06 am, GeorgeB > wrote:
> On Mon, 10 Dec 2007 09:23:52 -0800, Richard Riley
>
> > wrote:
> >If you're flying a homebuilt you can burn whatever you want - but the
> >alcohol restriction wasn't put there at random, it increases vapor
> >lock problems dramatically,
>
> How do the planes which do fly on ethanol handle that problem,
> pressurized tanks?
>
> >and is incompatable with many of the
> >materials commonly used in aircraft fuel systems.
>
> The sealant sloshed in the tanks is one, I think ...
>
> Do automobiles with flex-fuel capability do anything to minimize the
> vapor lock issues? I'm sure the materials were selected to be ok.

Most autos use electric in-tank fuel pumps now. When the
fuel is pushed to the engine there's little vapor-lock risk. Aircraft
still often use pumps on the engines that pull the fuel, so that the
pressure on the fuel in the lines drops and the vapor pressure of the
fuel will cause vapor lock under the right conditions. Low-wing
airplanes that have the tanks in the wings will have boost pumps
somewhere low in the system, but when they're turned off after takeoff
the risk of vapor lock rises with autofuels.
Remember the old high-school science demonstration of water
boiling at room temperature when a bell jar is placed over a bowl of
it and the air sucked out of the jar? The lowered atmospheric pressure
lowers the boiling point of the water. Gasoline has a higher vapor
pressure than water, so lowering the pressure on it will make it give
off vapors quickly, and those vapors displace the fuel in the lines
and prevent the fuel flow. The pump will be quite happy to pump
vapors, but carburetors and fuel injectors don't deal with vapors very
well, and the engine gets hungry and goes on strike.
A pump that sucks the fuel to lift it from the tank lowers the
fuel pressure between the tank and pump. A pump that pushes it upward
from the tank avoids that.


Dan

[[email protected]]

Compression ratio affects the efficiency of an engine, and something
called the 'brake specific fuel consumption' which is a measure of how
much fuel the engine must burn to produce some given amount of
horsepower... or something like that.

A higher compression ratio engine is more efficient in turning fuel
into useful work. But there are trade-offs in that a higher-
compression ratio is harder on the engine in terms of wear and tear,
and high compression needs higher octane fuel to prevent detonation
from happening inside the cylinders.

I have learned from the old-timers around my airport, that the 8.5:1
compression ratio 160hp version of the O-320 seems to be the sweet
spot, in that it can burn auto-fuel as long as you use premium
unleaded, 91 octane, and make sure you have big enough fuel lines that
are well-insulated from any heat source, and use a bigger, stronger
fuel pump system to prevent vapor-lock from happening. A 160hp O-320
that is throttled back to produce 150 hp will use less fuel per hour
than a 150hp low compression version of the same engine running at the
full 150hp power setting. The 160hp will also have cooler running
cylinder temps at that power setting too.

9:1 compression ratio in the otherwise same exact hypothetical O-320
will need 100LL to keep from suffering detonation, and will probably
suffer some anyway, and might be a maintenance headache, but it sure
will run strong when it's fresh.... for a little while anyway.

I had a buddy who built a Glasair III and had 10.5:1 pistons in his
IO-540. It sure was fast and strong, but he put a new set of pistons
in it about every 18 months. The old ones always came out with
multiple cracked rings, cracked ring grooves/lands, and sometimes
small holes melted between the dome and the 1st compression ring
groove. I think he must have had to work on that plane 20 hours of
repairs for each hour he flew it.

The 8.5:1 160hp O-320 seems to be the best proven choice for power
and longevity. I'd recommend that.

[Capt. Geoffrey Thorpe]

"Bob Fry" > wrote in message
...
>>>>>> "Scott" == Scott > writes:
>
> Scott> One thing I think "might" be a concern is that burning
> Scott> 100LL (can't get 80 octane avgas these days) in an engine
> Scott> built for 80 octane is the extra heat.
>
> Eh? Where's this "extra heat" come from? There is no practical unit
> energy difference between different octane fuels.
> --


Exactly. "Octane" is, by definition, a measure of a fuel's resistance to
knock under specific conditions. "High Octane" fuel does not burn any
hotter, generate any more power, or improve your fuel economy (note: see
exception below). Higher octane fuel lets the engine designer use a higher
compression ratio, or more spark advance, etc. without triggering knock. It
is the compression / spark changes that result in more power, etc.

Exception: _Some_ automobiles have sensors that detect knock and will adapt
the spark advance to match the fuel properties which will then improve your
fuel economy.

--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
When immigration is outlawed, only outlaws will immigrate.

[RST Engineering]

Oh, not this old wive's tale again. THERE IS NO ADDITIONAL HEAT GENERATED
BY A HIGHER OCTANE FUEL.

Jim

--
"If you think you can, or think you can't, you're right."
--Henry Ford

"Scott" > wrote in message
...
> One thing I think "might" be a concern is that burning 100LL (can't get 80
> octane avgas these days) in an engine built for 80 octane is the extra
> heat.

[Scott[_1_]]

Like I said, MIGHT ;) OK, if there is no difference in heat, what are
the 100 octane valves in my A-65 for? Or more generally, why do they
sell 100 octane valves for A-65s and C-85s, etc. that were certified on
80 octane??? Like I said, I use them, I don't wrench on 'em ;)

Scott


Bob Fry wrote:
>>>>>>"Scott" == Scott > writes:
>
>
> Scott> One thing I think "might" be a concern is that burning
> Scott> 100LL (can't get 80 octane avgas these days) in an engine
> Scott> built for 80 octane is the extra heat.
>
> Eh? Where's this "extra heat" come from? There is no practical unit
> energy difference between different octane fuels.

--
Scott
http://corbenflyer.tripod.com/
Gotta Fly or Gonna Die
Building RV-4 (Super Slow Build Version)

[Scott[_1_]]

See my other post and clue me in to why they sell 100 octane valves for
A-65s and C-85s. Are they a waste of money?

Scott


RST Engineering wrote:

> Oh, not this old wive's tale again. THERE IS NO ADDITIONAL HEAT GENERATED
> BY A HIGHER OCTANE FUEL.
>
> Jim
>

--
Scott
http://corbenflyer.tripod.com/
Gotta Fly or Gonna Die
Building RV-4 (Super Slow Build Version)

[[email protected]]

On Dec 10, 4:22 pm, Scott > wrote:
> See my other post and clue me in to why they sell 100 octane valves for
> A-65s and C-85s. Are they a waste of money?

See http://www.fsv2000.at/woche/2001_10/conti_sb_m77_3.pdf for a
TCM Service Bulletin about alternate valves for those engines. They
say that erosion problems have been encountered with the high lead
content of 100LL. It's not because the fuel burns hotter; it's a
corrosion issue. If the fuel burned hotter, I would see both higher
CHTs and more power out of my A-65. But I don't. You need to do some
research on Octane Ratings and Detonation. Google those.

Dan

[Capt. Geoffrey Thorpe]

"GeorgeB" > wrote in message
...
> On Mon, 10 Dec 2007 09:23:52 -0800, Richard Riley
> > wrote:
>
>>If you're flying a homebuilt you can burn whatever you want - but the
>>alcohol restriction wasn't put there at random, it increases vapor
>>lock problems dramatically,
>
> How do the planes which do fly on ethanol handle that problem,
> pressurized tanks?

The vapor pressure of ethanol alone (or gasoline alone) is less than a
gasoline ethanol mix. The maximum vapor pressure comes from about 10% to 20%
ethanol and 80% to 90% gasoline. I don't recall why - just what is.

>
>>and is incompatable with many of the
>>materials commonly used in aircraft fuel systems.
>
> The sealant sloshed in the tanks is one, I think ...
>
> Do automobiles with flex-fuel capability do anything to minimize the
> vapor lock issues? I'm sure the materials were selected to be ok.

They can run higher fuel pressures and/or increase the injector pulsewidth
as a function of measured or inferred fuel rail temperature. Another helpful
option is to have a system that returns excess fuel back to the tank which
tends to purge out any vapor bubbles.

--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
When immigration is outlawed, only outlaws will immigrate.

[Bill Daniels]

Let me reccomend a book. It's very old but packed with aero engine
knowledge. It's historically significant and a good read. Read it and
you'll know more about airplane piston engines than you could imagine there
was to know.

"The High Speed Internal Combustion Engine" by Sir Harry Ricardo.
See: http://www.ricardo.com/ricardoStore/product.asp?P_ID=149 (1968)

(In this case, "High Speed" refers to MPH and not neccessarilly RPM.)

Sir Harry was a British mechanical engineer whose most significant work was
between WW1 and WW2. He championed the sleeve valve engines that were
developed into the Bristol Centurion but his most historic work was on the
Rolls Royce Merlin. He also worked on the last generation of high power
piston engines like the Napier Nomad and consulted with all the US engine
manufacturers. He is a towering figure in the history of airplane piston
engine development.

His work with high octane fuels, supercharging and high compression ratios
is has been acknowledged as a major contribution to the Allied victory in
WW2.

Bill Daniels

[Matt Whiting]

wrote:
> Hi,
>
> So I was fantasizing the other day (as I do quite a bit) about my
> latest dream-plane-to-build: an RV-9A. (Note that this is fantasy in
> the extreme as I'm not a pilot yet AND I have no money!)
>
> I was thinking of how to power this plane. A Jet-A burning diesel
> would be great but that's another story. I spotted an ad for
> Superior's XP-series engines in Kitplanes. The website has a great
> "build your own engine" feature where you get to change all the bits
> and customize the engine.
>
> One of the things you have to choose is compression ratio: 7:1
> (150hp), 8.5:1 (160hp), or 9:1 (165hp).
> Going for the 7:1 option (from the default 8.5:1) adds $100 to the
> price! I'm assuming this is a supply/demand issue.
>
> So my question (finally) is: what is the effect of a higher or lower
> compression ratio? I believe TBO for all three engines is still 2000
> hours.
>
> - Is there a difference in wear?
> - Would maximum power be produced at the same RPM for all three
> engines? In other words is there a relationship like (power) =
> (compression ratio) x (RPM) such that these engines all operate at the
> same RPM? In which case wear would be the same...(?)
>
> For the RV-9A 150hp would be fine. I guess I'm trying to understand
> what benefit is to be had by spending the extra $100 to go for the
> lower compression pistons. All in my fantasy :)

I'm not sure, but I don't think the difference in compression ratios
will have a significant affect on wear or where the power peaks. The
main difference is that lower compression engines are more detonation
resistant and thus you have more margin to run low octane auto gas.

Matt

[Matt Whiting]

Kyle Boatright wrote:

> Max RPM is the same for all 3 engines, and the only wear difference should
> be on the connecting rods. Apparently the difference isn't enough to change
> the TBO, which is a theoretical figure anyway.

Connecting rods don't wear. Their bearings wear, but the con-rods don't
wear. I doubt the slight difference in force on the connecting rod and
crank bearings is enough to cause a measurable difference in wear.

Matt

[Matt Whiting]

Bob Fry wrote:
>>>>>> "Scott" == Scott > writes:
>
> Scott> One thing I think "might" be a concern is that burning
> Scott> 100LL (can't get 80 octane avgas these days) in an engine
> Scott> built for 80 octane is the extra heat.
>
> Eh? Where's this "extra heat" come from? There is no practical unit
> energy difference between different octane fuels.

Some believe that higher octane gasoline burns more slowly and thus can
put more fire past the exhaust valve. However, most of my reading on
the subject suggests that this is a myth and there is no substantial
difference in burn rate as a function of octane.

Matt

[Matt Whiting]

Scott wrote:
> Like I said, MIGHT ;) OK, if there is no difference in heat, what are
> the 100 octane valves in my A-65 for? Or more generally, why do they
> sell 100 octane valves for A-65s and C-85s, etc. that were certified on
> 80 octane??? Like I said, I use them, I don't wrench on 'em ;)

Because valves that were designed to be lubricated by the lead in leaded
fuel may not last long when using fuel with no or less lead.

Matt

[Peter Dohm]

"Capt. Geoffrey Thorpe" <The Sea Hawk at wow way d0t com> wrote in message
news:KP6dnV86MLVlRcDanZ2dnUVZ_vmlnZ2d@wideopenwest .com...
> "GeorgeB" > wrote in message
> ...
>> On Mon, 10 Dec 2007 09:23:52 -0800, Richard Riley
>> > wrote:
>>
>>>If you're flying a homebuilt you can burn whatever you want - but the
>>>alcohol restriction wasn't put there at random, it increases vapor
>>>lock problems dramatically,
>>
>> How do the planes which do fly on ethanol handle that problem,
>> pressurized tanks?
>
> The vapor pressure of ethanol alone (or gasoline alone) is less than a
> gasoline ethanol mix. The maximum vapor pressure comes from about 10% to
> 20% ethanol and 80% to 90% gasoline. I don't recall why - just what is.
>
>>
>>>and is incompatable with many of the
>>>materials commonly used in aircraft fuel systems.
>>
>> The sealant sloshed in the tanks is one, I think ...
>>
>> Do automobiles with flex-fuel capability do anything to minimize the
>> vapor lock issues? I'm sure the materials were selected to be ok.
>
> They can run higher fuel pressures and/or increase the injector pulsewidth
> as a function of measured or inferred fuel rail temperature. Another
> helpful option is to have a system that returns excess fuel back to the
> tank which tends to purge out any vapor bubbles.
>
> --
> Geoff
> The Sea Hawk at Wow Way d0t Com
> remove spaces and make the obvious substitutions to reply by mail
> When immigration is outlawed, only outlaws will immigrate.
>
I'm not sure, and also not qualified; but enough others are weighing in...

So, IIRC, the real issue with the STC is whether the fuel in question can be
reasonably asserted to conform to the same ASTM specification as the fuel
which was used for the test program for certification of the STC.

In the case of automobiles, the decision was made by governmental edict to
simply treat E10 the same as "pure" gasoline for automotive purposes.
However, that was not made applicable to certified aircraft engines; so all
of the testing would need to be done again to obtain a new STC. Speaking
only for myself, I would be reluctant to invest much effort or funding in
such a venture because the formulation of the fuel could be a moving
target--for example, next year mogas could magically become E15.

As to whether any, or all, of the other concerns are valid, I really don't
know. But, I do recall reading that the original specification regarding
vapor presure, which was indeed written to minimize vapor lock, may have
been written in error--shortly after WWI!

So, everyone else's guess is probably at least as good as mine.

Peter
Just my $0.02

[Kyle Boatright]

"Matt Whiting" > wrote in message
...
> Kyle Boatright wrote:
>
>> Max RPM is the same for all 3 engines, and the only wear difference
>> should be on the connecting rods. Apparently the difference isn't enough
>> to change the TBO, which is a theoretical figure anyway.
>
> Connecting rods don't wear. Their bearings wear, but the con-rods don't
> wear. I doubt the slight difference in force on the connecting rod and
> crank bearings is enough to cause a measurable difference in wear.

You're correct. My post was hastily composed and clearly didn't pass peer
review. ;-).

KB

>
> Matt

[Scott[_1_]]

FOUL!! 100LL has 4 times the lead content than the old 80 avgas and a
LOT more than unleaded auto! Therefore, the 100 octane valves should be
supper lubricated! But, in fact, the 80 octane valve tend to stick if
much 100LL is run through them...

So, somebody answer my question...what is special about 100 octane
valves? The ones I put in my A-65 were Stellite. What does Stellite
do? What about sodium filled valves? What's their claim to fame??

Scott


Matt Whiting wrote:
> Scott wrote:
>
>> Like I said, MIGHT ;) OK, if there is no difference in heat, what are
>> the 100 octane valves in my A-65 for? Or more generally, why do they
>> sell 100 octane valves for A-65s and C-85s, etc. that were certified
>> on 80 octane??? Like I said, I use them, I don't wrench on 'em ;)
>
>
> Because valves that were designed to be lubricated by the lead in leaded
> fuel may not last long when using fuel with no or less lead.
>
> Matt

--
Scott
http://corbenflyer.tripod.com/
Gotta Fly or Gonna Die
Building RV-4 (Super Slow Build Version)

[Blueskies]

"Matt Whiting" > wrote in message ...
>
> Connecting rods don't wear. Their bearings wear, but the con-rods don't wear. I doubt the slight difference in force
> on the connecting rod and crank bearings is enough to cause a measurable difference in wear.
>
> Matt

They do experience fatigue cycles. Is that wear?

[Bob Fry]

>>>>> "Scott" == Scott > writes:

Scott> Like I said, MIGHT ;) OK, if there is no difference in
Scott> heat, what are the 100 octane valves in my A-65 for? Or
Scott> more generally, why do they sell 100 octane valves for
Scott> A-65s and C-85s, etc. that were certified on 80 octane???
Scott> Like I said, I use them, I don't wrench on 'em ;)

I'm guessing--and this is just a guess--that their design differences
are solely to handle the considerable amount of lead still in 100
"low-lead" fuel. I use TCP in my C-90 to deal with the lead.
--
Happiness is an imaginary condition, formerly attributed by the living
to the dead, now usually attributed by adults to children, and by
children to adults.
~ Thomas Szasz

[Dale Alexander]

That depends on the BTU content of the fuel. The higher octane will allow
higher compression and tolerate heat better before knocking. Part of that
heat is the release of BTU energy. When I used to roadrace motorcycles long
ago in a mis-spent youth, I used a fuel made by ERC in Hayward. CA. The air
cooled bikes used stuff around 106 octane with about 18K BTU's. The water
cooled stuff could tolerate more BTU as the cooling system removed heat
before it became destructive. The fuel used for drag racing was rated at 22K
BTU. The engines would tolerate this heat release as it was for very short
times with an engine that was not fully warmed up. If this fuel was used in
an endurance event with one of our air-cooled engines, it would result in
holes in the pistons and seizures.

Now, what would 22K BTU stuff do in an 7 1/2 to 1 aircraft engine? Probably
nothing as the lower compression would limit the amount of work actually
being done. But it will still burn hotter than a fuel with a lower BTU
content. Might have to richen the mixture a bit if CHT or EGT were being
monitored, but knock and/or detonation won't be a problem.

One of the main benefits of using higher compression is the amount of power
available at part throttle. You can get more power out of a higher
compression engine at very low power settings than a lower compression
engine. The result of this is a lower fuel burn, unless the mixture is
richened to cool the cylinder. But cooling at part throttle shouldn't be an
issue all things being equal.

Dale Alexander

>>
>> Eh? Where's this "extra heat" come from? There is no practical unit
>> energy difference between different octane fuels.
>> --
>
>
> Exactly. "Octane" is, by definition, a measure of a fuel's resistance to
> knock under specific conditions. "High Octane" fuel does not burn any
> hotter, generate any more power, or improve your fuel economy (note: see
> exception below). Higher octane fuel lets the engine designer use a
> higher compression ratio, or more spark advance, etc. without triggering
> knock. It is the compression / spark changes that result in more power,
> etc.
>

[Dale Alexander]

As far as cars are concerned, for quite some time now, most vehicles have
had returnless systems where the pressure regulator and pump are in the
tank. The reason that fuel is not returned to the tank is that the fuel,
having made the trip to the fuel rail and back, has picked up heat. This
heat is released in the fuel tank, heating the fuel and increasing the fuel
tank pressure. This wrecks havoc with the evaporative emission systems
ability to detect leaks smaller than the current spec of 0.020".

Now with an aircraft, this shouldn't be a problem as there are now emission
systems on them...yet.

Dale Alexander

>
> They can run higher fuel pressures and/or increase the injector pulsewidth
> as a function of measured or inferred fuel rail temperature. Another
> helpful option is to have a system that returns excess fuel back to the
> tank which tends to purge out any vapor bubbles.
>
> --
> Geoff
> The Sea Hawk at Wow Way d0t Com
> remove spaces and make the obvious substitutions to reply by mail
> When immigration is outlawed, only outlaws will immigrate.
>

[Matt Whiting]

Scott wrote:
> FOUL!! 100LL has 4 times the lead content than the old 80 avgas and a
> LOT more than unleaded auto! Therefore, the 100 octane valves should be
> supper lubricated! But, in fact, the 80 octane valve tend to stick if
> much 100LL is run through them...
>
> So, somebody answer my question...what is special about 100 octane
> valves? The ones I put in my A-65 were Stellite. What does Stellite
> do? What about sodium filled valves? What's their claim to fame??
>
> Scott
>
>
> Matt Whiting wrote:
>> Scott wrote:
>>
>>> Like I said, MIGHT ;) OK, if there is no difference in heat, what
>>> are the 100 octane valves in my A-65 for? Or more generally, why do
>>> they sell 100 octane valves for A-65s and C-85s, etc. that were
>>> certified on 80 octane??? Like I said, I use them, I don't wrench on
>>> 'em ;)
>>
>>
>> Because valves that were designed to be lubricated by the lead in
>> leaded fuel may not last long when using fuel with no or less lead.
>>
>> Matt
>

No kidding. What's your point? I know that 100LL has a lot more lead
than 80. That doesn't change the correctness of my statement.

Matt

[Matt Whiting]

Blueskies wrote:
> "Matt Whiting" > wrote in message ...
>> Connecting rods don't wear. Their bearings wear, but the con-rods don't wear. I doubt the slight difference in force
>> on the connecting rod and crank bearings is enough to cause a measurable difference in wear.
>>
>> Matt
>
> They do experience fatigue cycles. Is that wear?

Maybe, maybe not. If the stress in steel remains below a certain
threshold, the fatigue life is essentially infinite. I've never heard
of a life limited con-rod so I suspect the stress levels are
sufficiently low that fatigue isn't an issue. In any event, no, I don't
think fatigue is considered to be wear by the standard definition.

Fatigue is a mode of deterioration, as is rust, but I don't think either
is considered to be wear per se.

Matt

[Dale Alexander]

Stellite is a very hard metal that does not transfer to the seating metal.
Valves and seats that are made of stellite do not wear at anywhere the rate
that older materials would. Use of hardened materials is one of the reasons
that contemporary engines (such as Toyota's) do not require a valve
clearance adjustment for the first ONE-EIGHTH of a MILLION MILES!!!

Elemental Sodium metal is liquid at temperatures that are common in a valve
stem. It is used in specially constructed valves that have hollow stems. As
the valve heats up, the Sodium becomes liquid. Now the trick is that the
hollow portion of the valve stem is not completely filled with Sodium. When
the valve opens,the Sodium will fill the end of the valve head (inside the
combustion chamber). Here it acts as a heat sink soaking up heat from the
exhaust gases as they exit the cylinder. When the valve moves to seat
itself, the heated Sodium moves to the valve stem area where the heat picked
up in the valve head area is transfered to the valve guide. This back and
forth transfer of heat helps keep the valve cool.

The downside of a Sodium filled valve is that the valve stem becomes quite
large. Because of this and the fact that better materials are now available,
they are not used on smaller bore engines as the increase in valve stem size
acts to reduce the amount of port area (in a critical area) needed to move
airflow in a high RPM engine. But in an inefficient aircraft engine where
heat is a larger concern that power, Sodium valves can be found.

Hope this helps,

Dale Alexander

"Scott" > wrote in message
.. .
> FOUL!! 100LL has 4 times the lead content than the old 80 avgas and a LOT
> more than unleaded auto! Therefore, the 100 octane valves should be
> supper lubricated! But, in fact, the 80 octane valve tend to stick if
> much 100LL is run through them...
>
> So, somebody answer my question...what is special about 100 octane valves?
> The ones I put in my A-65 were Stellite. What does Stellite do? What
> about sodium filled valves? What's their claim to fame??
>
> Scott
>
>
> Matt Whiting wrote:
>> Scott wrote:
>>
>>> Like I said, MIGHT ;) OK, if there is no difference in heat, what are
>>> the 100 octane valves in my A-65 for? Or more generally, why do they
>>> sell 100 octane valves for A-65s and C-85s, etc. that were certified on
>>> 80 octane??? Like I said, I use them, I don't wrench on 'em ;)
>>
>>
>> Because valves that were designed to be lubricated by the lead in leaded
>> fuel may not last long when using fuel with no or less lead.
>>
>> Matt
>
> --
> Scott
> http://corbenflyer.tripod.com/
> Gotta Fly or Gonna Die
> Building RV-4 (Super Slow Build Version)

[Big John]

On Tue, 11 Dec 2007 01:55:38 +0000, Scott >
wrote:

>FOUL!! 100LL has 4 times the lead content than the old 80 avgas and a
>LOT more than unleaded auto! Therefore, the 100 octane valves should be
>supper lubricated! But, in fact, the 80 octane valve tend to stick if
>much 100LL is run through them...
>
>So, somebody answer my question...what is special about 100 octane
>valves? The ones I put in my A-65 were Stellite. What does Stellite
>do? What about sodium filled valves? What's their claim to fame??
>
>Scott
>
>
>Matt Whiting wrote:
>> Scott wrote:
>>
>>> Like I said, MIGHT ;) OK, if there is no difference in heat, what are
>>> the 100 octane valves in my A-65 for? Or more generally, why do they
>>> sell 100 octane valves for A-65s and C-85s, etc. that were certified
>>> on 80 octane??? Like I said, I use them, I don't wrench on 'em ;)
>>
>>
>> Because valves that were designed to be lubricated by the lead in leaded
>> fuel may not last long when using fuel with no or less lead.
>>
>> Matt


Scott

High octane fuel burns slower in low compression engines. This lets
the flame front go out the exhaust valves and burn them if you run a
lot of hours.

We ran into this in the 'old' days when the fighters used 115-145
octane fuel. If we used that fuel in our cars we had to mix some oil
with it to prevent the burnt valves.Occasionally someone would burn a
tank full to clean their engine out (burn carbon off cylinders and
valves, etc)

This is probably the reason they put 100 octane valves in your low
compression engine so you could use 100 octane and not destroy the
valves?

Big John

[Scott[_1_]]

I understand your comment about the lack of lubrication from auto fuel,
but I was talking about 100LL...I never mentioned auto fuel in any of my
posts. I'm looking for an answer to why it was suggested that I put 100
octane valves in my A-65 if I was going to burn 100LL (I could have
replaced my valves with the standard 80 octane valves and continued to
burn auto fuel with Marvel Mystery oil mixed in for valve lubrication).

Scott


Matt Whiting wrote:
> Scott wrote:
>
>> FOUL!! 100LL has 4 times the lead content than the old 80 avgas and a
>> LOT more than unleaded auto! Therefore, the 100 octane valves should
>> be supper lubricated! But, in fact, the 80 octane valve tend to stick
>> if much 100LL is run through them...
>>
>> So, somebody answer my question...what is special about 100 octane
>> valves? The ones I put in my A-65 were Stellite. What does Stellite
>> do? What about sodium filled valves? What's their claim to fame??
>>
>> Scott
>>
>>
>> Matt Whiting wrote:
>>
>>> Scott wrote:
>>>
>>>> Like I said, MIGHT ;) OK, if there is no difference in heat, what
>>>> are the 100 octane valves in my A-65 for? Or more generally, why do
>>>> they sell 100 octane valves for A-65s and C-85s, etc. that were
>>>> certified on 80 octane??? Like I said, I use them, I don't wrench
>>>> on 'em ;)
>>>
>>>
>>>
>>> Because valves that were designed to be lubricated by the lead in
>>> leaded fuel may not last long when using fuel with no or less lead.
>>>
>>> Matt
>>
>>
>
> No kidding. What's your point? I know that 100LL has a lot more lead
> than 80. That doesn't change the correctness of my statement.
>
> Matt

--
Scott
http://corbenflyer.tripod.com/
Gotta Fly or Gonna Die
Building RV-4 (Super Slow Build Version)

[Peter Dohm]

"Matt Whiting" > wrote in message
...
> Bob Fry wrote:
>>>>>>> "Scott" == Scott > writes:
>>
>> Scott> One thing I think "might" be a concern is that burning
>> Scott> 100LL (can't get 80 octane avgas these days) in an engine
>> Scott> built for 80 octane is the extra heat. Eh? Where's this
>> "extra heat" come from? There is no practical unit
>> energy difference between different octane fuels.
>
> Some believe that higher octane gasoline burns more slowly and thus can
> put more fire past the exhaust valve. However, most of my reading on the
> subject suggests that this is a myth and there is no substantial
> difference in burn rate as a function of octane.
>
> Matt

I have not had occasion to test this premise on an aircraft engine--since
only 100LL was available when and where I flew. Therefore, no comparison
was possible.

However, back in the "bad ol' days", running a "regular gas" automobile
engine on "hi-test" had much the same effect as running with the ignition
timing retarded relative to that called for in the manual--the engine ran
noticeably warmer. Therefore, I am fairly certain that Big John is correct
in his assessment (elsewhere in this thread).

There is also the oft' stated issue of lead fouling, and it is possible that
the 100LL valves have some greater immunity to that as well; although I am
neither an engineer nor a wrench turner and I really have no idea how that
might be accomplished.

Peter

[Scott[_1_]]

Now that's getting to the info I'm asking. So, I should probably call
my valves stellite valves rather than 100 octane valves. Does being
harder make it harder for lead to stick to the stems? Maybe THAT's why
I need stellite (100 octane) valves...to keep them from sticking when
using 100LL??? That's why I went to stellite -- to keep my valves from
sticking (two tanks of 100LL and I stuck one valve and could not get it
unstuck)...

Scott


Dale Alexander wrote:

> Stellite is a very hard metal that does not transfer to the seating metal.
> Valves and seats that are made of stellite do not wear at anywhere the rate
> that older materials would. Use of hardened materials is one of the reasons
> that contemporary engines (such as Toyota's) do not require a valve
> clearance adjustment for the first ONE-EIGHTH of a MILLION MILES!!!
>
> Elemental Sodium metal is liquid at temperatures that are common in a valve
> stem. It is used in specially constructed valves that have hollow stems. As
> the valve heats up, the Sodium becomes liquid. Now the trick is that the
> hollow portion of the valve stem is not completely filled with Sodium. When
> the valve opens,the Sodium will fill the end of the valve head (inside the
> combustion chamber). Here it acts as a heat sink soaking up heat from the
> exhaust gases as they exit the cylinder. When the valve moves to seat
> itself, the heated Sodium moves to the valve stem area where the heat picked
> up in the valve head area is transfered to the valve guide. This back and
> forth transfer of heat helps keep the valve cool.
>
> The downside of a Sodium filled valve is that the valve stem becomes quite
> large. Because of this and the fact that better materials are now available,
> they are not used on smaller bore engines as the increase in valve stem size
> acts to reduce the amount of port area (in a critical area) needed to move
> airflow in a high RPM engine. But in an inefficient aircraft engine where
> heat is a larger concern that power, Sodium valves can be found.
>
> Hope this helps,
>
> Dale Alexander
>
> "Scott" > wrote in message
> .. .
>
>>FOUL!! 100LL has 4 times the lead content than the old 80 avgas and a LOT
>>more than unleaded auto! Therefore, the 100 octane valves should be
>>supper lubricated! But, in fact, the 80 octane valve tend to stick if
>>much 100LL is run through them...
>>
>>So, somebody answer my question...what is special about 100 octane valves?
>>The ones I put in my A-65 were Stellite. What does Stellite do? What
>>about sodium filled valves? What's their claim to fame??
>>
>>Scott
>>
>>
>>Matt Whiting wrote:
>>
>>>Scott wrote:
>>>
>>>
>>>>Like I said, MIGHT ;) OK, if there is no difference in heat, what are
>>>>the 100 octane valves in my A-65 for? Or more generally, why do they
>>>>sell 100 octane valves for A-65s and C-85s, etc. that were certified on
>>>>80 octane??? Like I said, I use them, I don't wrench on 'em ;)
>>>
>>>
>>>Because valves that were designed to be lubricated by the lead in leaded
>>>fuel may not last long when using fuel with no or less lead.
>>>
>>>Matt
>>
>>--
>>Scott
>>http://corbenflyer.tripod.com/
>>Gotta Fly or Gonna Die
>>Building RV-4 (Super Slow Build Version)
>
>
>

--
Scott
http://corbenflyer.tripod.com/
Gotta Fly or Gonna Die
Building RV-4 (Super Slow Build Version)

[Scott[_1_]]

OK, this is where I probably made my wrong assumption (even though I
precluded my original post with the word "might" when referring to more
heat from 100 octane). So it's not heat produced strictly because of
higher octane, it's just that the mixture may still be burning as the
exhaust valves open on the exhaust stroke and "burns" the valves. So,
it may not burn hotter, but it seems to burn longer, thus heating the
valves more, so it's kind of semantics since the valve is still getting
hotter by burning 100LL rather than 80 (but for a different reason than
I originally posted and ****ed everyone off by regurgitating an old
wive's tale). Is this correct?

Scott



Big John wrote:

> On Tue, 11 Dec 2007 01:55:38 +0000, Scott >
> wrote:
>
>
>>FOUL!! 100LL has 4 times the lead content than the old 80 avgas and a
>>LOT more than unleaded auto! Therefore, the 100 octane valves should be
>>supper lubricated! But, in fact, the 80 octane valve tend to stick if
>>much 100LL is run through them...
>>
>>So, somebody answer my question...what is special about 100 octane
>>valves? The ones I put in my A-65 were Stellite. What does Stellite
>>do? What about sodium filled valves? What's their claim to fame??
>>
>>Scott
>>
>>
>>Matt Whiting wrote:
>>
>>>Scott wrote:
>>>
>>>
>>>>Like I said, MIGHT ;) OK, if there is no difference in heat, what are
>>>>the 100 octane valves in my A-65 for? Or more generally, why do they
>>>>sell 100 octane valves for A-65s and C-85s, etc. that were certified
>>>>on 80 octane??? Like I said, I use them, I don't wrench on 'em ;)
>>>
>>>
>>>Because valves that were designed to be lubricated by the lead in leaded
>>>fuel may not last long when using fuel with no or less lead.
>>>
>>>Matt
>
>
>
> Scott
>
> High octane fuel burns slower in low compression engines. This lets
> the flame front go out the exhaust valves and burn them if you run a
> lot of hours.
>
> We ran into this in the 'old' days when the fighters used 115-145
> octane fuel. If we used that fuel in our cars we had to mix some oil
> with it to prevent the burnt valves.Occasionally someone would burn a
> tank full to clean their engine out (burn carbon off cylinders and
> valves, etc)
>
> This is probably the reason they put 100 octane valves in your low
> compression engine so you could use 100 octane and not destroy the
> valves?
>
> Big John

--
Scott
http://corbenflyer.tripod.com/
Gotta Fly or Gonna Die
Building RV-4 (Super Slow Build Version)

[Bob Fry]

>>>>> "MW" == Matt Whiting > writes:

MW> Scott wrote:
>> FOUL!! 100LL has 4 times the lead content than the old 80
>> avgas and a LOT more than unleaded auto! Therefore, the 100
>> octane valves should be supper lubricated! But, in fact, the
>> 80 octane valve tend to stick if much 100LL is run through
>> them... So, somebody answer my question...what is special
>> about 100 octane valves? The ones I put in my A-65 were
>> Stellite. What does Stellite do? What about sodium filled
>> valves? What's their claim to fame?? Scott
>> Matt Whiting wrote:
>>> Scott wrote:
>>>> Like I said, MIGHT ;) OK, if there is no difference in heat,
>>>> what are the 100 octane valves in my A-65 for? Or more
>>>> generally, why do they sell 100 octane valves for A-65s and
>>>> C-85s, etc. that were certified on 80 octane??? Like I said,
>>>> I use them, I don't wrench on 'em ;)
>>>
>>>
>>> Because valves that were designed to be lubricated by the lead
>>> in leaded fuel may not last long when using fuel with no or
>>> less lead.

MW> No kidding. What's your point? I know that 100LL has a lot
MW> more lead than 80. That doesn't change the correctness of my
MW> statement.

Your statement may be correct but is irrelevant. The OP asked "what
is different about valves designed for 100LL in an engine originally
designed for 80 octane avgas (which has a fraction of the lead as
100LL). You answered the reverse question.
--
All natural institutions of churches, whether Jewish, Christian, or
Turkish, appear to me no other than human inventions, set up to
terrify and enslave mankind, and monopolize power and profit.
~ Thomas Paine

[Bob Fry]

>>>>> "DA" == Dale Alexander > writes:

DA> Now, what would 22K BTU stuff do in an 7 1/2 to 1 aircraft
DA> engine? Probably nothing as the lower compression would limit
DA> the amount of work actually being done.

If I can reword your statement to "what would higher octane stuff
do..." then I can answer not probably, but definitely, it will not do
anything different, if the only difference between the two fuels is
octane.

DA> But it will still burn
DA> hotter than a fuel with a lower BTU content.

Where did the difference in "BTU content" (i.e. unit chemical energy
content) come from? Not from a mere octane enhancer. Perhaps the
fuels used in your road racing experience had not only different
octanes, but also different unit energies.

>>> Eh? Where's this "extra heat" come from? There is no
>>> practical unit energy difference between different octane
>>> fuels. --
>>
>>
>> Exactly. "Octane" is, by definition, a measure of a fuel's
>> resistance to knock under specific conditions. "High Octane"
>> fuel does not burn any hotter, generate any more power, or
>> improve your fuel economy (note: see exception below). Higher
>> octane fuel lets the engine designer use a higher compression
>> ratio, or more spark advance, etc. without triggering knock. It
>> is the compression / spark changes that result in more power,
>> etc.
>>



--
"He is not only dull himself; he is the cause of dullness in others."
-Samuel Johnson

[Dale Alexander]

Octane and BTU are two different qualities of fuel. In a very simplistic
view, the longer the molecule, the more energy it takes to break it. By
needing more energy to break, it is more resistant to knocking or detonation
(not the same but still applicable). This would be octane.

BTU is the amount of energy that the chemical reaction will produce AFTER
the reaction has started. Compression, or lack of it, would reduce the
amount of pressure thus heat that the reaction would ultimately make. In a
system that is optimized (tuned) all of the heat energy possible may be
extracted. But even in a lower compression engine, an increase in heat would
be available as there is more potential in the first place. So no, the only
difference is NOT octane.

As I said, very simplistic but serves to illustrate the point.

By the way, I seem to remember a research paper that stated that
conventional motor fuels (not alcohol or nitro based, just for
clarification) burn at the same rate no matter the octane. I think that
confusion exists here in that a previous poster stated that higher octane
fuels burn slower. A lower octane fuel may "seem" to burn faster, but what
may be happening is that the normal flame front increases the pressure in
the remaining unignited mixture to the point of self-ignition and the
resulting second flame front advances to meet the first in a reduced period
of time. Still burning at the same rate but from two different starting
points and meetin gin the middle. This is abnormal combustion though and in
a normal combustion event, the fuels would burn at the same rate.

"Bob Fry" > wrote in message
...
>>>>>> "DA" == Dale Alexander > writes:
>
> DA> Now, what would 22K BTU stuff do in an 7 1/2 to 1 aircraft
> DA> engine? Probably nothing as the lower compression would limit
> DA> the amount of work actually being done.
>
> If I can reword your statement to "what would higher octane stuff
> do..." then I can answer not probably, but definitely, it will not do
> anything different, if the only difference between the two fuels is
> octane.
>
> DA> But it will still burn
> DA> hotter than a fuel with a lower BTU content.
>
> Where did the difference in "BTU content" (i.e. unit chemical energy
> content) come from? Not from a mere octane enhancer. Perhaps the
> fuels used in your road racing experience had not only different
> octanes, but also different unit energies.

Yes, the fuels used were different and proprietary blends that I was not
privy to. I was just a comsumer, not a business partner. But the fuels were
blended for specific purposes using various chemical qualities to achieve
end results. This I stated previously.

It seems that ERC is still in business. See

http://www.ercracingfuels.com/sxs1.htm

for a comparision of various blends. It would appear that their ERC MUL/A is
the fuel that I used in my motors and the ERC 1-19A is the 120 octane stuff.
But look around the website and find that various fuels do not have a direct
relationship between octane and BTU. So something other than octane is
definitely going on here. Read some of the descriptions of the bases and
blending to see what qualities they build the fuel for.

>
> >>> Eh? Where's this "extra heat" come from? There is no
> >>> practical unit energy difference between different octane
> >>> fuels. --

See above


> >>
> >>
> >> Exactly. "Octane" is, by definition, a measure of a fuel's
> >> resistance to knock under specific conditions. "High Octane"
> >> fuel does not burn any hotter, generate any more power, or
> >> improve your fuel economy (note: see exception below). Higher
> >> octane fuel lets the engine designer use a higher compression
> >> ratio, or more spark advance, etc. without triggering knock. It
> >> is the compression / spark changes that result in more power,
> >> etc.
> >>

You are correct that optimization of the engine as you mention will result
in more power, mileage etc. But we learned that you have to watch out for
the BTU as well. And an engine can generate too much heat and power to the
point of reducing power without ever suffering from pinging, knocking or
detonation. But that is a subject for another day.

I love this group! It would be great to sit down to a dinner conversation
with many of you. A lot of accumulated knowledge in this group..

[[email protected]]

On Dec 10, 2:32 pm, "RST Engineering" > wrote:
> Oh, not this old wive's tale again. THERE IS NO ADDITIONAL HEAT GENERATED
> BY A HIGHER OCTANE FUEL.
>
> Jim
>----------------------------------------------------------------------------------------------

Gee, Jim... that can't be right. Because if it IS, it means 99 &
44/100% of the 'experts' out there are WRONG...

:-)

[cavelamb himself[_4_]]

wrote:

> On Dec 10, 2:32 pm, "RST Engineering" > wrote:
>
>>Oh, not this old wive's tale again. THERE IS NO ADDITIONAL HEAT GENERATED
>>BY A HIGHER OCTANE FUEL.
>>
>>Jim
>>----------------------------------------------------------------------------------------------
>
>
> Gee, Jim... that can't be right. Because if it IS, it means 99 &
> 44/100% of the 'experts' out there are WRONG...
>
> :-)


That's just about right...

[RST Engineering]

Only if they are Ivory and it is Snowing

{;-)

Jim

--
"If you think you can, or think you can't, you're right."
--Henry Ford

> wrote in message
...
> On Dec 10, 2:32 pm, "RST Engineering" > wrote:
>> Oh, not this old wive's tale again. THERE IS NO ADDITIONAL HEAT
>> GENERATED
>> BY A HIGHER OCTANE FUEL.
>>
>> Jim
>>----------------------------------------------------------------------------------------------
>
> Gee, Jim... that can't be right. Because if it IS, it means 99 &
> 44/100% of the 'experts' out there are WRONG...
>
> :-)

[RST Engineering]

I do, and I do.

100 octane valves have a different seat angle and a smaller stem diameter
than 80 octane valves.

Lead is the big problem with 100 octane in a low compression engine. While
the gasoline itself and the combustion process makes not a whit of
difference in the temperature of combustion, the compression ratio does.
Gasoline in a high compression engine burns hotter, be it 80 or 100 octane.
Tetraethyl lead requires a relatively high temperature to be completely
vaporized and exhausted in the combustion process. A high compression
engine does this, while a low compression engine does not. Bromine is
introduced to the mixture in an attempt to "help" the lead "burn", but even
bromine doesn't do much in a low temperature environment.

The different seat angle is an attempt to "get the lead out" of unburned
tetraethyl lead. Even so, the low temperatures encountered in a low
compression engine lets the lead coagulate on the first cool surface it
finds. That happens to be the valve stem. Therefore, the valve stems are
ever so slightly reduced (.005" comes to mind) so that the lead can plate
out on the valve stem and still not cause the stem to stick on the guide so
often. "So often" is the operative term here. 100 octane will cause valve
sticking, but with the 100 octane valves, just not quite as soon.

Jim

--
"If you think you can, or think you can't, you're right."
--Henry Ford

"Scott" > wrote in message
.. .

> Like I said, MIGHT ;) OK, if there is no difference in heat, what are the
> 100 octane valves in my A-65 for? Or more generally, why do they sell 100
> octane valves for A-65s and C-85s, etc. that were certified on 80
> octane??? Like I said, I use them, I don't wrench on 'em ;)
>
> Scott

[[email protected]]

On Dec 11, 6:57 am, "RST Engineering" > wrote:

> The different seat angle is an attempt to "get the lead out" of unburned
> tetraethyl lead. Even so, the low temperatures encountered in a low
> compression engine lets the lead coagulate on the first cool surface it
> finds. That happens to be the valve stem. Therefore, the valve stems are
> ever so slightly reduced (.005" comes to mind) so that the lead can plate
> out on the valve stem and still not cause the stem to stick on the guide so
> often. "So often" is the operative term here. 100 octane will cause valve
> sticking, but with the 100 octane valves, just not quite as soon.
>
> Jim
>
That lines up with what we used to experience with the small
Continentals. The valves tended to stick if the stem/guide clearances
were set at the minimum spec. The other problem with many small
engines is their mixture: the Stromberg carb either had no mixture
control, or it was safety-wired at full rich. So the engine gets too
much fuel, which was OK when 80/87 was available, but it's not OK with
100LL which has four times the TEL spec. My A-65 runs much leaner and
the valves don't get fouled up.

Dan

[RST Engineering]

The actual truth of the matter is that 80/87 was allowed a MAXIMUM of 0.5
grams of TEL in a gallon, but in practice after the 1940s, no TEL was needed
to make spec. Since TEL is a hell of a lot more expensive than gasoline,
there was virtually no TEL in 80 from the 1950s on.

100LL on the other hand needs every bit of the allowable 2 grams/gallon to
meet spec, so in fact there is an huge increase in the lead content.

Jim

> much fuel, which was OK when 80/87 was available, but it's not OK with
> 100LL which has four times the TEL spec.

[Jim Logajan]

"RST Engineering" > wrote:
> Oh, not this old wive's tale again. THERE IS NO ADDITIONAL HEAT
> GENERATED BY A HIGHER OCTANE FUEL.

My understanding is that you are correct, yet not fully correct. At the end
of the combustion phase of the cycle there is no significant difference in
the amount of heat released between a high octane and low octane fuel.

BUT - one is more likely to burn unevenly and/or more quickly (i.e.
"knocking" or "pinging") which leads either to unplanned overpressures or
localized hot-spots (i.e. _high heat concentrations_). So sure - no _final_
difference in released energy, but time and space concentrations can result
in metal melting or breaking in one case and not the other.

I suppose one analogy would be to consider the difference between what a
bullet does to the human body versus what eating a large meal does. The
bullet may have about as much energy as the large meal (probably even less
than the meal), but the bullet will do a lot more damage to you than the
meal. ;-) It's all in how quickly the energy is released and the manner of
the release.

[Morgans[_2_]]

"Jim Logajan" > wrote

> BUT - one is more likely to burn unevenly and/or more quickly (i.e.
> "knocking" or "pinging") which leads either to unplanned overpressures or
> localized hot-spots (i.e. _high heat concentrations_). So sure - no
> _final_
> difference in released energy, but time and space concentrations can
> result
> in metal melting or breaking in one case and not the other.

So, in your example, the high octane would be the cooler burning fuel,
because it burns more evenly, and slowly, so it prevents knocking.

Other scientific data showes that the higher octane fuel, the lower the /btu
content. That's fact. Not a lot of difference, but a difference, none the
less.

> I suppose one analogy would be to consider the difference between what a
> bullet does to the human body versus what eating a large meal does. The
> bullet may have about as much energy as the large meal (probably even less
> than the meal), but the bullet will do a lot more damage to you than the
> meal. ;-) It's all in how quickly the energy is released and the manner of
> the release.

I don't see your analogy having anything to do with the discussion of octane
and valve differences.
--
Jim in NC

[Jim Logajan]

"Morgans" > wrote:
> "Jim Logajan" > wrote
>> I suppose one analogy would be to consider the difference between
>> what a bullet does to the human body versus what eating a large meal
>> does. The bullet may have about as much energy as the large meal
>> (probably even less than the meal), but the bullet will do a lot more
>> damage to you than the meal. ;-) It's all in how quickly the energy
>> is released and the manner of the release.
>
> I don't see your analogy having anything to do with the discussion of
> octane and valve differences.

It wasn't intended to address that specific aspect. It was an analogy,
maybe a lousy one, but it's not like I get paid to do them!

:-)

[Capt. Geoffrey Thorpe]

"Matt Whiting" > wrote in message
...
<...> Some believe that higher octane gasoline burns more slowly and thus
can
> put more fire past the exhaust valve. However, most of my reading on the
> subject suggests that this is a myth and there is no substantial
> difference in burn rate as a function of octane.
>
> Matt

Burn rates are essentially the same.

There are problems (in automobiles) with some premium auto fuels since the
changes in the chemistry to get higher octane can result in slower
evaporation which can cause an engine to stumble when you first step on the
gas.

--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
When immigration is outlawed, only outlaws will immigrate.

[Darrel Toepfer]

Jim Logajan > wrote:
> "Morgans" > wrote:
>> "Jim Logajan" > wrote
>>> I suppose one analogy would be to consider the difference between
>>> what a bullet does to the human body versus what eating a large meal
>>> does. The bullet may have about as much energy as the large meal
>>> (probably even less than the meal), but the bullet will do a lot
>>> more damage to you than the meal. ;-) It's all in how quickly the
>>> energy is released and the manner of the release.
>>
>> I don't see your analogy having anything to do with the discussion of
>> octane and valve differences.
>
> It wasn't intended to address that specific aspect. It was an analogy,
> maybe a lousy one, but it's not like I get paid to do them!
>
>:-)

Here's one, maybe it depends on which end the meal made gas depart the
body?

[Jim Logajan]

"Morgans" > wrote:
> "Jim Logajan" > wrote
>
>> BUT - one is more likely to burn unevenly and/or more quickly (i.e.
>> "knocking" or "pinging") which leads either to unplanned
>> overpressures or localized hot-spots (i.e. _high heat
>> concentrations_). So sure - no _final_
>> difference in released energy, but time and space concentrations can
>> result
>> in metal melting or breaking in one case and not the other.
>
> So, in your example, the high octane would be the cooler burning fuel,
> because it burns more evenly, and slowly, so it prevents knocking.

Except that it appears what I wrote is not correct. :-(

The octane rating appears to be a measure of the activation energy of
combustion, not a measure of the combustion rate.

[jerry wass]

GeorgeB wrote:
> On Mon, 10 Dec 2007 09:23:52 -0800, Richard Riley
> > wrote:
>
>> If you're flying a homebuilt you can burn whatever you want - but the
>> alcohol restriction wasn't put there at random, it increases vapor
>> lock problems dramatically,
>
> How do the planes which do fly on ethanol handle that problem,
> pressurized tanks?
>
>> and is incompatable with many of the
>> materials commonly used in aircraft fuel systems.
>
> The sealant sloshed in the tanks is one, I think ...
>
> Do automobiles with flex-fuel capability do anything to minimize the
> vapor lock issues? I'm sure the materials were selected to be ok.

Ole Jerry said: most of the automobiles in the last 20 yrs or so have
the GAS PUMP inside the GAS Tank. Vapor lock is usually induced by
Sucking on the fuel at some point in the fuel system.

[Bill Daniels]

"Jerry Wass" > wrote in message
. net...
> GeorgeB wrote:
>> On Mon, 10 Dec 2007 09:23:52 -0800, Richard Riley
>> > wrote:
>>
>>> If you're flying a homebuilt you can burn whatever you want - but the
>>> alcohol restriction wasn't put there at random, it increases vapor
>>> lock problems dramatically,
>>
>> How do the planes which do fly on ethanol handle that problem,
>> pressurized tanks?
>>
>>> and is incompatable with many of the
>>> materials commonly used in aircraft fuel systems.
>>
>> The sealant sloshed in the tanks is one, I think ...
>>
>> Do automobiles with flex-fuel capability do anything to minimize the
>> vapor lock issues? I'm sure the materials were selected to be ok.
>
> Ole Jerry said: most of the automobiles in the last 20 yrs or so have the
> GAS PUMP inside the GAS Tank. Vapor lock is usually induced by Sucking on
> the fuel at some point in the fuel system.

Maybe off topic but this involves fuel pumps in tanks. They fail way too
often and when they do, you aren't going to fix it on the road side. After
five failures at $800 a pop, I removed the pump from the tank and put an
aftermarket pump in the fuel line where I can replace it with a screw driver
for $50. No vapor locks yet.

[clare at snyder.on.ca]

On Mon, 10 Dec 2007 14:32:55 -0800, "RST Engineering"
> wrote:

>Oh, not this old wive's tale again. THERE IS NO ADDITIONAL HEAT GENERATED
>BY A HIGHER OCTANE FUEL.
>
>Jim
And, by default, high octane gasoline is NOT slower burning. SOME high
octane fuels MAY burn slower, but others WILL burn faster. The
air/fuel ratio has a more predictable effect on burn speed.

--
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[clare at snyder.on.ca]

On Mon, 10 Dec 2007 23:17:23 +0000, Scott >
wrote:

>Like I said, MIGHT ;) OK, if there is no difference in heat, what are
>the 100 octane valves in my A-65 for? Or more generally, why do they
>sell 100 octane valves for A-65s and C-85s, etc. that were certified on
>80 octane??? Like I said, I use them, I don't wrench on 'em ;)
>
>Scott

It has to do with the difference in lead content from what I have
gathered. 100LL has a LOT of lead, and an A65 will get "morning
sickness" quite early in it's life if run on 100LL with standard
valves without agressive leaning.
>
>
>Bob Fry wrote:
>>>>>>>"Scott" == Scott > writes:
>>
>>
>> Scott> One thing I think "might" be a concern is that burning
>> Scott> 100LL (can't get 80 octane avgas these days) in an engine
>> Scott> built for 80 octane is the extra heat.
>>
>> Eh? Where's this "extra heat" come from? There is no practical unit
>> energy difference between different octane fuels.


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[clare at snyder.on.ca]

On Mon, 10 Dec 2007 19:25:31 -0500, "Capt. Geoffrey Thorpe" <The Sea
Hawk at wow way d0t com> wrote:

>"GeorgeB" > wrote in message
...
>> On Mon, 10 Dec 2007 09:23:52 -0800, Richard Riley
>> > wrote:
>>
>>>If you're flying a homebuilt you can burn whatever you want - but the
>>>alcohol restriction wasn't put there at random, it increases vapor
>>>lock problems dramatically,
>>
>> How do the planes which do fly on ethanol handle that problem,
>> pressurized tanks?
>
>The vapor pressure of ethanol alone (or gasoline alone) is less than a
>gasoline ethanol mix. The maximum vapor pressure comes from about 10% to 20%
>ethanol and 80% to 90% gasoline. I don't recall why - just what is.
>
>>
>>>and is incompatable with many of the
>>>materials commonly used in aircraft fuel systems.
>>
>> The sealant sloshed in the tanks is one, I think ...
>>
>> Do automobiles with flex-fuel capability do anything to minimize the
>> vapor lock issues? I'm sure the materials were selected to be ok.
>
>They can run higher fuel pressures and/or increase the injector pulsewidth
>as a function of measured or inferred fuel rail temperature. Another helpful
>option is to have a system that returns excess fuel back to the tank which
>tends to purge out any vapor bubbles.

Not only purges bubbles but also cools the lines. The pump moves
multiple quantities of fuel compared to what the engine actually
consumes (on some vehicles as much as TEN TIMES.- but most closer to
3)

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[clare at snyder.on.ca]

On Tue, 11 Dec 2007 01:23:01 GMT, Matt Whiting >
wrote:

wrote:
>> Hi,
>>
>> So I was fantasizing the other day (as I do quite a bit) about my
>> latest dream-plane-to-build: an RV-9A. (Note that this is fantasy in
>> the extreme as I'm not a pilot yet AND I have no money!)
>>
>> I was thinking of how to power this plane. A Jet-A burning diesel
>> would be great but that's another story. I spotted an ad for
>> Superior's XP-series engines in Kitplanes. The website has a great
>> "build your own engine" feature where you get to change all the bits
>> and customize the engine.
>>
>> One of the things you have to choose is compression ratio: 7:1
>> (150hp), 8.5:1 (160hp), or 9:1 (165hp).
>> Going for the 7:1 option (from the default 8.5:1) adds $100 to the
>> price! I'm assuming this is a supply/demand issue.
>>
>> So my question (finally) is: what is the effect of a higher or lower
>> compression ratio? I believe TBO for all three engines is still 2000
>> hours.
>>
>> - Is there a difference in wear?
>> - Would maximum power be produced at the same RPM for all three
>> engines? In other words is there a relationship like (power) =
>> (compression ratio) x (RPM) such that these engines all operate at the
>> same RPM? In which case wear would be the same...(?)
>>
>> For the RV-9A 150hp would be fine. I guess I'm trying to understand
>> what benefit is to be had by spending the extra $100 to go for the
>> lower compression pistons. All in my fantasy :)
>
>I'm not sure, but I don't think the difference in compression ratios
>will have a significant affect on wear or where the power peaks. The
>main difference is that lower compression engines are more detonation
>resistant and thus you have more margin to run low octane auto gas.
>
>Matt
And that is only true to a point.
A case in point.
The Corvair engine with the low compression ratio "smog" or "open"
heads is significantly MORE detonation prone than the non smog or
"closed chamber" high compression heads. Also, lowering the
compression ratio of the high compression engine by using thicker head
sealing rings (gaskets) actually CAUSES detonation, rather than
reducing it. The difference in quench and squish is AT LEAST as
significant as compression ratio as far as detonation is concerned.

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[clare at snyder.on.ca]

On Tue, 11 Dec 2007 01:27:52 GMT, Matt Whiting >
wrote:

>Scott wrote:
>> Like I said, MIGHT ;) OK, if there is no difference in heat, what are
>> the 100 octane valves in my A-65 for? Or more generally, why do they
>> sell 100 octane valves for A-65s and C-85s, etc. that were certified on
>> 80 octane??? Like I said, I use them, I don't wrench on 'em ;)
>
>Because valves that were designed to be lubricated by the lead in leaded
>fuel may not last long when using fuel with no or less lead.
>
>Matt
Good arguement EXCEPT 100LL has MORE lead than the early 80 octane. It
is only low in lead compared to the earlier 100/115 or whatever the
"real beetle juice" was rated at.

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[clare at snyder.on.ca]

On Tue, 11 Dec 2007 01:55:38 +0000, Scott >
wrote:

>FOUL!! 100LL has 4 times the lead content than the old 80 avgas and a
>LOT more than unleaded auto! Therefore, the 100 octane valves should be
>supper lubricated! But, in fact, the 80 octane valve tend to stick if
>much 100LL is run through them...
>
>So, somebody answer my question...what is special about 100 octane
>valves? The ones I put in my A-65 were Stellite. What does Stellite
>do? What about sodium filled valves? What's their claim to fame??
>
>Scott
>
The 100 octane valves will have different valve stem design (and
likely clearances) and will (from what I've read on the subject) be
designed to run HOTTER to keep the TEL from building up on the tulip
portion and the neck of the valve. This is what causes the "morning
sickness" referred to as hanging valves - otherwise known as "lead
poisoning". Aggressive leaning at less than peak power will also help
reduce this lead build-up.

Stellite can stand a LOT more heat. Sodium cooled valves have liquid
sodium inside the stem and head to act like a "heat pipe" and suck the
heat down the stem to transfer the heat more efficiently to the head.
This would cause the stem area to run hotter, possibly explaining
their use in 100ll conversion valves?
>
>Matt Whiting wrote:
>> Scott wrote:
>>
>>> Like I said, MIGHT ;) OK, if there is no difference in heat, what are
>>> the 100 octane valves in my A-65 for? Or more generally, why do they
>>> sell 100 octane valves for A-65s and C-85s, etc. that were certified
>>> on 80 octane??? Like I said, I use them, I don't wrench on 'em ;)
>>
>>
>> Because valves that were designed to be lubricated by the lead in leaded
>> fuel may not last long when using fuel with no or less lead.
>>
>> Matt


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[clare at snyder.on.ca]

On Tue, 11 Dec 2007 01:57:26 GMT, "Blueskies"
> wrote:

>
>"Matt Whiting" > wrote in message ...
>>
>> Connecting rods don't wear. Their bearings wear, but the con-rods don't wear. I doubt the slight difference in force
>> on the connecting rod and crank bearings is enough to cause a measurable difference in wear.
>>
>> Matt
>
>They do experience fatigue cycles. Is that wear?
>
Fatique cycles in a properly designed rod are almost immaterial. There
is virtually NO bending motion, In compression steel is almost totally
unaffected, and the rods are generally designed to take the tension
loading from high RPM - which is not directly affected by higher
compression. High compression engines that are run at extreme speeds
DO need to worry about fatigue cycles. "tractor engines" as a rule
have no such worries. (unless you are talking "pulling tractors")

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[clare at snyder.on.ca]

On Tue, 11 Dec 2007 03:40:42 +0000, Scott >
wrote:

>OK, this is where I probably made my wrong assumption (even though I
>precluded my original post with the word "might" when referring to more
>heat from 100 octane). So it's not heat produced strictly because of
>higher octane, it's just that the mixture may still be burning as the
>exhaust valves open on the exhaust stroke and "burns" the valves. So,
>it may not burn hotter, but it seems to burn longer, thus heating the
>valves more, so it's kind of semantics since the valve is still getting
>hotter by burning 100LL rather than 80 (but for a different reason than
>I originally posted and ****ed everyone off by regurgitating an old
>wive's tale). Is this correct?
>
>Scott

Not necessarily.
By definition high octane fuel does NOT burn slower than regular gas.
Burning FASTER would be more productive in reducing detonation.
Counterintuitive, but DEFINITELY true. The faster the burn, the less
heart absorbed by the "end gasses" in the chamber, and the less chance
they will "dissassociate" and destabilize - which IS what causes
detonation. Gasoline BURNS. Hydrogen radicals EXPLODE.
To prevent detonation you need to burn cooler, burn faster, or the
fuel needs tobe more resistant to thermal dissassosiation .

This is why detonation is GENERALLY only a problem at lower RPMs. You
can produce X HP at 2500 RPM and get detonation, and 1.5X at 3200 RPM,
for instance, with no detonation. - with the same or higher cyl
pressures at the higher speed.
>
>
>
>Big John wrote:
>
>> On Tue, 11 Dec 2007 01:55:38 +0000, Scott >
>> wrote:
>>
>>
>>>FOUL!! 100LL has 4 times the lead content than the old 80 avgas and a
>>>LOT more than unleaded auto! Therefore, the 100 octane valves should be
>>>supper lubricated! But, in fact, the 80 octane valve tend to stick if
>>>much 100LL is run through them...
>>>
>>>So, somebody answer my question...what is special about 100 octane
>>>valves? The ones I put in my A-65 were Stellite. What does Stellite
>>>do? What about sodium filled valves? What's their claim to fame??
>>>
>>>Scott
>>>
>>>
>>>Matt Whiting wrote:
>>>
>>>>Scott wrote:
>>>>
>>>>
>>>>>Like I said, MIGHT ;) OK, if there is no difference in heat, what are
>>>>>the 100 octane valves in my A-65 for? Or more generally, why do they
>>>>>sell 100 octane valves for A-65s and C-85s, etc. that were certified
>>>>>on 80 octane??? Like I said, I use them, I don't wrench on 'em ;)
>>>>
>>>>
>>>>Because valves that were designed to be lubricated by the lead in leaded
>>>>fuel may not last long when using fuel with no or less lead.
>>>>
>>>>Matt
>>
>>
>>
>> Scott
>>
>> High octane fuel burns slower in low compression engines. This lets
>> the flame front go out the exhaust valves and burn them if you run a
>> lot of hours.
>>
>> We ran into this in the 'old' days when the fighters used 115-145
>> octane fuel. If we used that fuel in our cars we had to mix some oil
>> with it to prevent the burnt valves.Occasionally someone would burn a
>> tank full to clean their engine out (burn carbon off cylinders and
>> valves, etc)
>>
>> This is probably the reason they put 100 octane valves in your low
>> compression engine so you could use 100 octane and not destroy the
>> valves?
>>
>> Big John


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[clare at snyder.on.ca]

On Mon, 10 Dec 2007 20:38:01 -0800, Bob Fry >
wrote:

>>>>>> "DA" == Dale Alexander > writes:
>
> DA> Now, what would 22K BTU stuff do in an 7 1/2 to 1 aircraft
> DA> engine? Probably nothing as the lower compression would limit
> DA> the amount of work actually being done.
>
>If I can reword your statement to "what would higher octane stuff
>do..." then I can answer not probably, but definitely, it will not do
>anything different, if the only difference between the two fuels is
>octane.
>
> DA> But it will still burn
> DA> hotter than a fuel with a lower BTU content.
>
>Where did the difference in "BTU content" (i.e. unit chemical energy
>content) come from? Not from a mere octane enhancer. Perhaps the
>fuels used in your road racing experience had not only different
>octanes, but also different unit energies.

Racing fuel, generally, is not even CLOSE to gasoline. It is a very
complex witches brew, and generally significantly higher specific
gravity, as well as higher BTU per gallon (not necessarily more BTU
per lb, hence the higher SG)
>
> >>> Eh? Where's this "extra heat" come from? There is no
> >>> practical unit energy difference between different octane
> >>> fuels. --
> >>
> >>
> >> Exactly. "Octane" is, by definition, a measure of a fuel's
> >> resistance to knock under specific conditions. "High Octane"
> >> fuel does not burn any hotter, generate any more power, or
> >> improve your fuel economy (note: see exception below). Higher
> >> octane fuel lets the engine designer use a higher compression
> >> ratio, or more spark advance, etc. without triggering knock. It
> >> is the compression / spark changes that result in more power,
> >> etc.
> >>


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[clare at snyder.on.ca]

On Tue, 11 Dec 2007 16:19:46 -0500, "Morgans"
> wrote:

>
>"Jim Logajan" > wrote
>
>> BUT - one is more likely to burn unevenly and/or more quickly (i.e.
>> "knocking" or "pinging") which leads either to unplanned overpressures or
>> localized hot-spots (i.e. _high heat concentrations_). So sure - no
>> _final_
>> difference in released energy, but time and space concentrations can
>> result
>> in metal melting or breaking in one case and not the other.
>
>So, in your example, the high octane would be the cooler burning fuel,
>because it burns more evenly, and slowly, so it prevents knocking.

High and low octane fuel burn at the same rate. Hydrogen burns much
faster. Detonation involves "cracking" of the fuel, releasing unstable
hydrogen radicals which explode instead of burning.
>
>Other scientific data showes that the higher octane fuel, the lower the /btu
>content. That's fact. Not a lot of difference, but a difference, none the
>less.

High octane fuel does not BY DEFAULT have a lower BTU content.
Straight run high octane would be as high or higher in BTUs than
straight run regular. HOWEVER the additives used to increase the
octane in MOST high octane pump gas today are significantly lower in
BTU content than the gasoline they are added to. Look at Ethanol, as
an example. E10 has 10% ethanol, and ethanol has roughly half the btu
value of gasoline, so E10 has roughly 5% less BTU per gallon.
It is also less dense, so the BTU per lb may not be that much lower -
but we do not measure our fuel by weight.




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[clare at snyder.on.ca]

On Tue, 11 Dec 2007 23:36:24 -0000, Jim Logajan >
wrote:

>"Morgans" > wrote:
>> "Jim Logajan" > wrote
>>
>>> BUT - one is more likely to burn unevenly and/or more quickly (i.e.
>>> "knocking" or "pinging") which leads either to unplanned
>>> overpressures or localized hot-spots (i.e. _high heat
>>> concentrations_). So sure - no _final_
>>> difference in released energy, but time and space concentrations can
>>> result
>>> in metal melting or breaking in one case and not the other.
>>
>> So, in your example, the high octane would be the cooler burning fuel,
>> because it burns more evenly, and slowly, so it prevents knocking.
>
>Except that it appears what I wrote is not correct. :-(
>
>The octane rating appears to be a measure of the activation energy of
>combustion, not a measure of the combustion rate.

And not the activation energy of NORMAL combustion. Octane relates
STRICTLY to the resistance to thermal dissassociation of the fuel in
the combustion chamber. Under high heat and pressure gasoline/air
mixtures can "come unglued" letting the hydrogen "flake off" so to
speak. The hydrogen, which normally likes to hang around in couples
(as H2) starts running around as H1- an unstable and promiscuous
radical that will couple with anything available - in this case excess
O2 particals - and when this happens, ALL HELL BREAKS LOOSE inside the
cyl..

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[clare at snyder.on.ca]

On Tue, 11 Dec 2007 18:08:03 -0700, "Bill Daniels"
<bildan@comcast-dot-net> wrote:

>
>"Jerry Wass" > wrote in message
. net...
>> GeorgeB wrote:
>>> On Mon, 10 Dec 2007 09:23:52 -0800, Richard Riley
>>> > wrote:
>>>
>>>> If you're flying a homebuilt you can burn whatever you want - but the
>>>> alcohol restriction wasn't put there at random, it increases vapor
>>>> lock problems dramatically,
>>>
>>> How do the planes which do fly on ethanol handle that problem,
>>> pressurized tanks?
>>>
>>>> and is incompatable with many of the
>>>> materials commonly used in aircraft fuel systems.
>>>
>>> The sealant sloshed in the tanks is one, I think ...
>>>
>>> Do automobiles with flex-fuel capability do anything to minimize the
>>> vapor lock issues? I'm sure the materials were selected to be ok.
>>
>> Ole Jerry said: most of the automobiles in the last 20 yrs or so have the
>> GAS PUMP inside the GAS Tank. Vapor lock is usually induced by Sucking on
>> the fuel at some point in the fuel system.
>
>Maybe off topic but this involves fuel pumps in tanks. They fail way too
>often and when they do, you aren't going to fix it on the road side. After
>five failures at $800 a pop, I removed the pump from the tank and put an
>aftermarket pump in the fuel line where I can replace it with a screw driver
>for $50. No vapor locks yet.
>
Strange. I have 362000km on my current vehicle (pump in tank - still
original and 14 years old) and had 240,000 on each of my last two
vehicles - 14 and 18 years old - all on the original in-tank pumps.

I NEVER got that kind of mileage out of a mechanical pump, and frame
mounted electric pumps virtually ALL rusted out in less than 10 years,
requiring replacement. This is why, to a large degree, most
manufacturers went to in-tank pumps a long time ago.
If you don't change fuel filters, you WILL burn out pumps. If you
always run on the bottom 1/4 tank you will LIKELY burn out pumps - but
the top 1/4 doesn't cost any more to keep full than the bottom 1/4.

--
Posted via a free Usenet account from http://www.teranews.com

[Dale Alexander]

Yeah, I might have gone over the top there with that comparison. But the
subsequent posts started into high octane not burning any hotter and I used
the info that I was familiar with. Everybody was so damned sure that high
octane didn't burn any hotter and I knew of instances where that was not
true. I listed my sources with a website for the manufacturer of the fuel I
was using as a reference. You could put an end to this by showing a source
that definitively showed that in every instance (with regard to aviation
fuel), there is no difference in heat output or flame speed between the
various fuels.

By the way, other than vapor pressure, do you believe that there is a
difference between winter and summer blends of automotive fuels?

And if you don't mind my asking, what is your training/schooling in this
field? The statements I have seen attributed to you show a disciplined mind.

Dale Alexander

<clare at snyder.on.ca> wrote in message
...
> On Mon, 10 Dec 2007 20:38:01 -0800, Bob Fry >
> wrote:

>
> Racing fuel, generally, is not even CLOSE to gasoline. It is a very
> complex witches brew, and generally significantly higher specific
> gravity, as well as higher BTU per gallon (not necessarily more BTU
> per lb, hence the higher SG)
>>
>> >>> Eh? Where's this "extra heat" come from? There is no
>> >>> practical unit energy difference between different octane
>> >>> fuels. --
>> >>

[Scott[_1_]]

OK, so us poor bastages with A-65s with no mixture control might be
screwed anyways :( Anybody have any ideas on how to get a mixture
control onto an A-65? If I recall, my carb is an NAS3A1 Stromberg. I
THINK there might be a plate on top of the carb where a mixture control
may have been present at one time???

Scott



>>
>
Aggressive leaning at less than peak power will also help
> reduce this lead build-up.
>

[Bob Fry]

>>>>> "Scott" == Scott > writes:

Scott> OK, so us poor bastages with A-65s with no mixture control
Scott> might be screwed anyways :( Anybody have any ideas on how
Scott> to get a mixture control onto an A-65? If I recall, my
Scott> carb is an NAS3A1 Stromberg. I THINK there might be a
Scott> plate on top of the carb where a mixture control may have
Scott> been present at one time???

Can't answer that question, but you might try adding TCP to your fuel
to help scavenge the lead out.

--
We choose our joys and sorrows long before we experience them.
~ Kahlil Gibran

[Scott[_1_]]

I will check into that...



Bob Fry wrote:
>>>>>>"Scott" == Scott > writes:
>
>
> Scott> OK, so us poor bastages with A-65s with no mixture control
> Scott> might be screwed anyways :( Anybody have any ideas on how
> Scott> to get a mixture control onto an A-65? If I recall, my
> Scott> carb is an NAS3A1 Stromberg. I THINK there might be a
> Scott> plate on top of the carb where a mixture control may have
> Scott> been present at one time???
>
> Can't answer that question, but you might try adding TCP to your fuel
> to help scavenge the lead out.
>

--
Scott
http://corbenflyer.tripod.com/
Gotta Fly or Gonna Die
Building RV-4 (Super Slow Build Version)

[clare at snyder.on.ca]

On Tue, 11 Dec 2007 20:18:54 -0800, "Dale Alexander"
> wrote:

>Yeah, I might have gone over the top there with that comparison. But the
>subsequent posts started into high octane not burning any hotter and I used
>the info that I was familiar with. Everybody was so damned sure that high
>octane didn't burn any hotter and I knew of instances where that was not
>true. I listed my sources with a website for the manufacturer of the fuel I
>was using as a reference. You could put an end to this by showing a source
>that definitively showed that in every instance (with regard to aviation
>fuel), there is no difference in heat output or flame speed between the
>various fuels.
>
>By the way, other than vapor pressure, do you believe that there is a
>difference between winter and summer blends of automotive fuels?

Definitely. In most cases the formulation is quite different.
>
>And if you don't mind my asking, what is your training/schooling in this
>field? The statements I have seen attributed to you show a disciplined mind.
>
>Dale Alexander

I am a long time (now semi-retired) auto mechanic, former auto shop
instructor at both secondary and trade level, and quite widely read on
the subject. I tend to be "curious" and research things quite
thoroughly when trying to get a handle on something.

I am also a partner in a Pegazair project which will be flying a
lightly modified Corvair engine.
>
><clare at snyder.on.ca> wrote in message
...
>> On Mon, 10 Dec 2007 20:38:01 -0800, Bob Fry >
>> wrote:
>
>>
>> Racing fuel, generally, is not even CLOSE to gasoline. It is a very
>> complex witches brew, and generally significantly higher specific
>> gravity, as well as higher BTU per gallon (not necessarily more BTU
>> per lb, hence the higher SG)
>>>
>>> >>> Eh? Where's this "extra heat" come from? There is no
>>> >>> practical unit energy difference between different octane
>>> >>> fuels. --
>>> >>
>


--
Posted via a free Usenet account from http://www.teranews.com

[[email protected]]

On Dec 12, 5:03 am, Scott > wrote:
> OK, so us poor bastages with A-65s with no mixture control might be
> screwed anyways :( Anybody have any ideas on how to get a mixture
> control onto an A-65? If I recall, my carb is an NAS3A1 Stromberg. I
> THINK there might be a plate on top of the carb where a mixture control
> may have been present at one time???

That's it. Finding the bits and pieces might be a hassle. I
made mine, since it's a homebuilt, and it works OK. It's a back-
suction type of mixture control, where the lever rotates a valve under
that cover. There's a hole into the float bowl, another into the dead
airspace behind the venturi, and another into the venturi itself. The
area behind the venturi is at roughly atmospheric pressure, and the
venturi, of course, is much lower than that. The mixture control
valve, when rotated toward "Lean," gradually shuts off that port to
the dead airspace, allowing the venturi port to start sucking against
the fuel in the bowl. That decreases the differential pressures at the
fuel nozzle and flow decreases.
It won't work as an idle cutoff. There's so little flow through
the venturi at idle that nothing happens when you pull the mixture all
the way out. Carbs with idle cutoff are using a valve inside the carb
that varies the flow of the fuel itself from the main jet in the
bottom of the bowl, so that if it's pulled full lean, all flow,
including idle fuel, stops.

Dan

[Scott[_1_]]

Mine is in an experimental as well, so I'll see if I can find more info
on getting or making some sort of mixture control...thanks for the info!

Scott


wrote:

> On Dec 12, 5:03 am, Scott > wrote:
>
>>OK, so us poor bastages with A-65s with no mixture control might be
>>screwed anyways :( Anybody have any ideas on how to get a mixture
>>control onto an A-65? If I recall, my carb is an NAS3A1 Stromberg. I
>>THINK there might be a plate on top of the carb where a mixture control
>>may have been present at one time???
>
>
> That's it. Finding the bits and pieces might be a hassle. I
> made mine, since it's a homebuilt, and it works OK. It's a back-
> suction type of mixture control, where the lever rotates a valve under
> that cover. There's a hole into the float bowl, another into the dead
> airspace behind the venturi, and another into the venturi itself. The
> area behind the venturi is at roughly atmospheric pressure, and the
> venturi, of course, is much lower than that. The mixture control
> valve, when rotated toward "Lean," gradually shuts off that port to
> the dead airspace, allowing the venturi port to start sucking against
> the fuel in the bowl. That decreases the differential pressures at the
> fuel nozzle and flow decreases.
> It won't work as an idle cutoff. There's so little flow through
> the venturi at idle that nothing happens when you pull the mixture all
> the way out. Carbs with idle cutoff are using a valve inside the carb
> that varies the flow of the fuel itself from the main jet in the
> bottom of the bowl, so that if it's pulled full lean, all flow,
> including idle fuel, stops.
>
> Dan

--
Scott
http://corbenflyer.tripod.com/
Gotta Fly or Gonna Die
Building RV-4 (Super Slow Build Version)

[Cy Galley]

No extra heat in high Octane. Same hydrocarbon structure is both. Same
BTUs. Only difference is the speed of combustion is controlled so it is
slower in the higher octane to prevent pre-ignition.
--
Cy Galley - Chair,
AirVenture Emergency Aircraft Repair
A 46 Year Service Project of Chapter 75
EAA Safety Programs Editor - TC
New address -
EAA Sport Pilot


"Scott" > wrote in message
...
> One thing I think "might" be a concern is that burning 100LL (can't get 80
> octane avgas these days) in an engine built for 80 octane is the extra
> heat. I think valves are most likely to be affected by burning the 100LL
> instead of 80. Might be all wet on this, but that's what I've heard and
> I'm NOT an engine mechanic...just a user :) You might try digging in the
> Lycoming site and see what they say about 80 vs 100LL...
>
> Scott
>
>
> wrote:
>> OK, not cool to reply to my own post, I know. But I just found this
>> great resource which basically answers all my questions:
>>
>> http://www.lycoming.textron.com/support/tips-advice/key-reprints/
>>
>> "Lycoming provides helpful information in various publications,
>> including Lycoming Flyer Key Reprints. Lycoming's Key
>> Reprints is our effort to continually share our best practices,
>> key lessons and engines systems knowledge to empower
>> our customers."
>>
>> Lower compression => lower chance of preignition => lower octane
>> required (ie. auto fuel)!
>> Yes, that would make a difference to the pocket book!
>>
>> The issue of using auto fuel is addressed in this series also:
>>
>> "Auto fuel is now being used as a substitute for Grade 80
>> aviation gasoline under STCs issued by the FAA. Most
>> major oil companies and engine manufacturers continue
>> to recommend that aircraft piston engines be operated
>> only on aviation gasoline. Deterioration of engine and fuel
>> system parts have been reported in aircraft using auto
>> fuel. Operators should consider the added risk of using
>> auto fuel in aircraft. Remember -- a pilot can't pull over
>> to the side of the road when fuel creates a problem with
>> the engine."
>>
>>
>
> --
> Scott
> http://corbenflyer.tripod.com/
> Gotta Fly or Gonna Die
> Building RV-4 (Super Slow Build Version)

[clare at snyder.on.ca]

On Thu, 13 Dec 2007 04:00:58 GMT, "Cy Galley" >
wrote:

>No extra heat in high Octane. Same hydrocarbon structure is both. Same
>BTUs. Only difference is the speed of combustion is controlled so it is
>slower in the higher octane to prevent pre-ignition.


WAY off base, Cy.
On ALL counts, except the no extra heat and same BTU's.

--
Posted via a free Usenet account from http://www.teranews.com

[[email protected]]

On Dec 12, 9:08 pm, clare at snyder.on.ca wrote:
> On Thu, 13 Dec 2007 04:00:58 GMT, "Cy Galley" >
> wrote:
>
> >No extra heat in high Octane. Same hydrocarbon structure is both. Same
> >BTUs. Only difference is the speed of combustion is controlled so it is
> >slower in the higher octane to prevent pre-ignition.
>
> WAY off base, Cy.
> On ALL counts, except the no extra heat and same BTU's.
>
> --
> Posted via a free Usenet account fromhttp://www.teranews.com

Higher-octane rated fuels have about the same flame front
speed as lower-octane fuels, at around 100 feet per second. It's their
resistance to detonation, which involves flame fronts speeds of 5000
feet per second or more, that makes them necessary in high-compression
engines. As the combustion process begins in the cylinder, the burning
raises the pressure through the entire air/fuel mix, and low-octane
rated fuels will break down under that increasing pressure and
spontaneously combine with the oxygen, igniting almost all at once
instead of *waiting* (key word) for the flame to set them off in a
controlled chain reaction.
Detonation therefore requires time to develop. Low RPM with
high MP is pro-detonation. Lean mixtures burn more slowly, so they're
pro-detonation. Big cylinders take more time for the flame front to
cross, so they suffer more from detonation.
Preignition is something else. It's ignition of the mix
during compression by some hot spot in the cylinder, perhaps a glowing
bit of carbon in the head or on the piston. The burn begins early,
before the sparkplug was scheduled to fire, and gets way ahead of
itself due to the still-increasing compression as well as the
combustion, and detonation might happen. The damage is about the same.
Engines that aren't leaned properly will develop more carbon to cause
preignition. Too much lead fouling can do it. An oil-burner will
carbon up, too.
Octane ratings are different than octane content. In the old
way, fuel under test was fed to a variable-compression test engine and
the compression was raised until detonation began to occur. Then that
fuel was shut off and a mix of octane and heptane was introduced,
engine still running, and the octane/heptane ratio was varied until
the detonation point was established. An 80-octane fuel had the same
detonation characteristics as a mix of 80% octane and 20% heptane,
hence the rating. 80/87 reflected the detonation resistance at lean
and rich settings.
Fuels with ratings above 100 obviously have to be rated using
some other method, since we can't have a fuel consisting of, say, 115%
octane.

Dan

[Big John]

On Thu, 13 Dec 2007 04:00:58 GMT, "Cy Galley" >
wrote:

>No extra heat in high Octane. Same hydrocarbon structure is both. Same
>BTUs. Only difference is the speed of combustion is controlled so it is
>slower in the higher octane to prevent pre-ignition.



Cy

I'm on your side. See my prior post.

Lot of people are using different words to describe the same thing
which may be part of the problem.

Big John