Mogas: what happens to EGTs?

[Stu Gotts]

This was a little fun quiz that was circulated on a type specific
email list a few days ago. It was authored by George Braly of
Advanced Pilot Seminars, and principle of GAMI. If you're familiar
with George, you know he backs everything up with HARD DATA obtained
from his own research. In a couple of days I'll post the correct
answers (no, I didn't get them all) so that most can learn and a few
can refute. Have fun.

Ok... little MOGAS quiz for you.

You run the Left tank dry and fill it up with premium unleaded car
gas.

Right tank has 100LL.

Takeoff on the RH tank and climb, level off, and set up the mixture
for
cruise flight. Either ROP or LOP. Your choice.


THEN, you switch to the LEFT tank. You change nothing else.

Later you download your JPI and plot the data.

1 What is it going to show happened to the EGTs when you switched
tanks?

2 What is it going to show happened to the CHTS when you switched
tanks?

3 (not in the JPI, but: ) What is the airspeed going to do? Increase?
Decrease? Stay the same?

Why?

[Jim Weir]

->
->1 What is it going to show happened to the EGTs when you switched
->tanks?

The EGT should show a very slight increase. The higher the octane, the smoother
and cooler the burn. You have gone from 100 octane to (arguably) 87 or 93
octane and the car gas should burn hotter.


->
->2 What is it going to show happened to the CHTS when you switched
->tanks?

If the EGT (internal temperature of the cylinders) goes up, the CHT must follow
suit, but at an even reduced value as regards the EGT rise.


->
->3 (not in the JPI, but: ) What is the airspeed going to do? Increase?
->Decrease? Stay the same?

Increase, ever so slightly. The efficiency (and therefore power output) of any
Carnot cycle engine is a function of the temperature difference between intake
and exhaust temperatures. If the intake remains constant (ambient) and the
exhaust rises, the horsepower produced goes up and the airspeed...EVER SO
SLIGHTLY...increases.

Then again, I'm a sparky. What the hell do I know about engines.


Jim



Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com

[Addison Laurent]

On Sun, 07 Mar 2004 11:34:57 -0500, Jim Weir wrote:
> ->
> ->1 What is it going to show happened to the EGTs when you switched
> ->tanks?
>
> The EGT should show a very slight increase. The higher the octane, the
> smoother and cooler the burn. You have gone from 100 octane to
> (arguably) 87 or 93 octane and the car gas should burn hotter.

I was under the (perhaps mistaken) understanding that mogas was measured
on a differing octane rating system, and that 93 mogas was ~100 octane
measured on the avgas system? (The question specified "premium" mogas).

Given that, I'd have thought everything would have been the same, across
the board.

Addison

[john smith]

Stu Gotts wrote:
> 1 What is it going to show happened to the EGTs when you switched
> tanks?

I was taught that 87 and 100LL avgas burns at the same temperature. The
octane only allows the flame front to propagate smoothly through the
cylinder. Autogas is a different formulation, so it may burn at a
different temperature.
If autogas burns cooler, the EGTs will decrease. If autogas burns
hotter, the EGTs will increase.

> 2 What is it going to show happened to the CHTS when you switched
> tanks?

CHTs will follow EGTs.


> 3 (not in the JPI, but: ) What is the airspeed going to do? Increase?
> Decrease? Stay the same?
> Why?

Depends on the energy content of the fuel, not the temperature. Pistons
work on pressure. The more energy released by the fuel, the more
pressure is generated to drive the piston. More energy means the engine
is turning faster (higher torque?). More torque transmitted to the prop
produces more airspeed.

That's my reasoning.

[G.R. Patterson III]

Addison Laurent wrote:
>
> I was under the (perhaps mistaken) understanding that mogas was measured
> on a differing octane rating system, and that 93 mogas was ~100 octane
> measured on the avgas system?

They use a different system, but it works the other way 'round. There is no mogas
that comes close to 100 octane avgas. Fortunately, most engines that are burning
100LL are actually certified for a lower octane.

According the the EAA fact sheet on autogas, you can get a good idea of the
octane equivalent by subtracting 5 from the mogas anti-knock index (the "octane"
rating on the pump). So 93 octane mogas would be about 88 octane on the avgas
scale.

http://www.eaa.org/education/fuel/detonation.html

George Patterson
Battle, n; A method of untying with the teeth a political knot that would
not yield to the tongue.

[Tom Sixkiller]

"john smith" > wrote in message
...
> Stu Gotts wrote:
> > 1 What is it going to show happened to the EGTs when you switched
> > tanks?
>
> I was taught that 87 and 100LL avgas burns at the same temperature. The
> octane only allows the flame front to propagate smoothly through the
> cylinder. Autogas is a different formulation, so it may burn at a
> different temperature.
> If autogas burns cooler, the EGTs will decrease. If autogas burns
> hotter, the EGTs will increase.

http://www.avweb.com/news/columns/182149-1.html

April 27, 2002

Pelican's Perch #55:
Lead in the Hogwash

Tetraethyl lead has been gone from automobile gasoline for two decades, and
it's only a matter of time before leaded avgas goes away as well. Despite a
huge amount of industry research, nobody yet has a suitable replacement
fuel, and nobody's yet quite sure what will happen to today's piston-powered
fleet when the supply of 100LL dries up. AVweb's John Deakin dispels a bunch
of myths about TEL, explains what it does and why it's so indispensable in
high-performance recips, and talks about one solution to the coming
unleaded-avgas crisis that actually works.

[Tom Sixkiller]

"G.R. Patterson III" > wrote in message
...
>
>
> Addison Laurent wrote:
> >
> > I was under the (perhaps mistaken) understanding that mogas was measured
> > on a differing octane rating system, and that 93 mogas was ~100 octane
> > measured on the avgas system?
>
> They use a different system, but it works the other way 'round. There is
no mogas
> that comes close to 100 octane avgas. Fortunately, most engines that are
burning
> 100LL are actually certified for a lower octane.
>
> According the the EAA fact sheet on autogas, you can get a good idea of
the
> octane equivalent by subtracting 5 from the mogas anti-knock index (the
"octane"
> rating on the pump). So 93 octane mogas would be about 88 octane on the
avgas
> scale.
>
> http://www.eaa.org/education/fuel/detonation.html
>

And this article as well:
http://www.avweb.com/news/columns/182132-1.html

May 27, 2001

Pelican's Perch #43:
Detonation Myths

We've all been taught about detonation in piston aircraft engines. It's what
occurs when combustion pressure and temperature get so high that the
fuel/air mixture to explodes violently instead of burning smoothly, and it
can destroy an engine in a matter of seconds. Right? Well, not exactly.
AVweb's John Deakin reviews the latest research, and demonstrates that
detonation occurs in various degrees - much like icing and turbulence - with
the milder forms not being particularly harmful. Heavy detonation is
definitely destructive, and the Pelican offers some concrete data on how to
avoid it.

[Newps]

Jim Weir wrote:

> ->
> ->1 What is it going to show happened to the EGTs when you switched
> ->tanks?
>
> The EGT should show a very slight increase. The higher the octane, the smoother
> and cooler the burn. You have gone from 100 octane to (arguably) 87 or 93
> octane and the car gas should burn hotter.

Are not the auto and aviation octane scales different?

[Tom Sixkiller]

"Newps" > wrote in message
news:1UQ2c.82422$PR3.1197113@attbi_s03...
>
>
> Jim Weir wrote:
>
> > ->
> > ->1 What is it going to show happened to the EGTs when you switched
> > ->tanks?
> >
> > The EGT should show a very slight increase. The higher the octane, the
smoother
> > and cooler the burn. You have gone from 100 octane to (arguably) 87 or
93
> > octane and the car gas should burn hotter.
>
> Are not the auto and aviation octane scales different?
>

From http://www.avweb.com/news/columns/182149-1.html

April 27, 2002

Pelican's Perch #55:
Lead in the Hogwash

By John Deakin

"If the theory of "octane" is simple, the numbers are not. It is a very
common mistake in pilot lounges and coffee shops to talk about octane at the
gas pump where you fill your automobile, and the pump where you fill your
airplane. The calculations are VERY DIFFERENT, and they cannot be directly
compared! It's like talking about knots vs. miles per hour, or using
"gallons." Is that American gallons, or imperial gallons? There are several
entirely different ways of measuring "octane." There is "Research Octane
Number" (RON), "Motor Octane Number" (MON), "(R+M)/2" which is nothing more
than an average of the two, and "Observed Road Octane Number," (RdON).

Finally, there is the octane number we talk about in GA. It is close to
"Motor Octane Number" but not identical. So much for standards. Actually,
there are fairly good reasons for several different octane measurements, as
"octane" works differently in different situations (race engines, road
engines, aircraft engines, air cooled vs. water cooled, intake air
temperature, RPM, etc.). For more on this, there's a short but decent
explanation at http://www.osbornauto.com/octane.htm."

[Stu Gotts]

Before this morfs into how the innkeeper built his homemade fuel
pumper, I thought I would post the answers. I'm surprised many more
didn't take a shot at this but then again, it's not regular hangar
chat. How well did you do?

EGT = Exhaust Gas Temperature
CHT = Cylinder Head Temperature
ROP = Rich of Peak
LOP = Lean of Peak
(and I should have listed this earlier, sorry!)


The lower octane should cause a faster overall burn time and short
interval to peak pressure - - and that should result in lower EGTs.

For the same reasons, the peak pressure increase should cause higher
CHTs.

And the horsepower ?? It probably would not change much... 1-2 % .

The overall effect is the same as if you had improperly advanced the
timing 3-7 degrees.

Regards, George

Contact George at gami.com for any further explanations.






>Ok... little MOGAS quiz for you.
>
>You run the Left tank dry and fill it up with premium unleaded car
>gas.
>
>Right tank has 100LL.
>
>Takeoff on the RH tank and climb, level off, and set up the mixture
>for
>cruise flight. Either ROP or LOP. Your choice.
>
>
>THEN, you switch to the LEFT tank. You change nothing else.
>
>Later you download your JPI and plot the data.
>
>1 What is it going to show happened to the EGTs when you switched
>tanks?
>
>2 What is it going to show happened to the CHTS when you switched
>tanks?
>
>3 (not in the JPI, but: ) What is the airspeed going to do? Increase?
>Decrease? Stay the same?
>
>Why?
>

[Jim Weir]

Stu Gotts >
shared these priceless pearls of wisdom:

->Before this morfs into how the innkeeper built his homemade fuel
->pumper, I thought I would post the answers. I'm surprised many more
->didn't take a shot at this but then again, it's not regular hangar
->chat. How well did you do?

The innkeeper built his homemade fuel pumper after seeing the plans that a
sparky gave him at an Oshkosh forum, but to the point...

Now to the point -- I thought you said that your source had DONE the experiment
and HAD data. People who have been there and done that don't say "SHOULD" and
"PROBABLY", they say "DID". I think you've dicked the problem without hard
data.


Jim


->
->EGT = Exhaust Gas Temperature
->CHT = Cylinder Head Temperature
->ROP = Rich of Peak
->LOP = Lean of Peak
->(and I should have listed this earlier, sorry!)
->
->
->The lower octane should cause a faster overall burn time and short
^^^^^^
->interval to peak pressure - - and that should result in lower EGTs.
^^^^^^
->
->For the same reasons, the peak pressure increase should cause higher
^^^^^^
->CHTs.
->
->And the horsepower ?? It probably would not change much... 1-2 % .
^^^^^^^
->
->The overall effect is the same as if you had improperly advanced the
->timing 3-7 degrees.
->
->Regards, George
->
->Contact George at gami.com for any further explanations.
->
->
->
->
->
->
->>Ok... little MOGAS quiz for you.
->>
->>You run the Left tank dry and fill it up with premium unleaded car
->>gas.
->>
->>Right tank has 100LL.
->>
->>Takeoff on the RH tank and climb, level off, and set up the mixture
->>for
->>cruise flight. Either ROP or LOP. Your choice.
->>
->>
->>THEN, you switch to the LEFT tank. You change nothing else.
->>
->>Later you download your JPI and plot the data.
->>
->>1 What is it going to show happened to the EGTs when you switched
->>tanks?
->>
->>2 What is it going to show happened to the CHTS when you switched
->>tanks?
->>
->>3 (not in the JPI, but: ) What is the airspeed going to do? Increase?
->>Decrease? Stay the same?
->>
->>Why?
->>

Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com

[jls]

"Newps" > wrote in message
news:1UQ2c.82422$PR3.1197113@attbi_s03...
>
>
> Jim Weir wrote:
>
> > ->
> > ->1 What is it going to show happened to the EGTs when you switched
> > ->tanks?
> >
> > The EGT should show a very slight increase. The higher the octane, the
smoother
> > and cooler the burn.

I don't think I agree with this last sentence. First of all the burn may
be just as smooth with a lower octane with a low compression engine. High
octane fuel like 100LL has no benefits for an A-65 Continental engine with
6.3:1 compression ratio and loves the 80 octane gasoline it was designed
for.

And if the burn is cooler when 100LL (rather than 80) is run through the
carb, why is it the engine must have special 100LL exhaust valves, which are
designed with high-temperature alloys?


You have gone from 100 octane to (arguably) 87 or 93
> > octane and the car gas should burn hotter.
>
> Are not the auto and aviation octane scales different?
>

I don't know the answer but I tell you what I suspect. I suspect the egt
of 100LL will be higher. Think about it and correct me if I'm wrong. The
low compression Continentals when they are rebuilt -- the A-65's, O-200's,
and O-300's --- have optional 100-octane exhaust valves available from the
parts supply houses like Fresno Airparts. Now WHY is that, other than
because the mix is still burning when the exhaust valve opens? My
suspicion. You (anyone) tell me, with an intelligent explanation, if I'm
wrong.

Higher octane gasoline like 100LL, furthermore, is a little less volatile
than mogas and burns more slowly because of the higher RON numbers, so that
when the exhaust valve opens combustion is less complete than with the same
charge of mogas -- in the low-compression O-300. So if you're running
100LL in an O-300-powered 172, why do you need 100-octane exhaust valves,
whose faces are something like inconel or another exotic alloy designed for
temperatures much higher than the stock exhaust valves?

[Jim Weir]

" jls" >
shared these priceless pearls of wisdom:

->
->And if the burn is cooler when 100LL (rather than 80) is run through the
->carb, why is it the engine must have special 100LL exhaust valves, which are
->designed with high-temperature alloys?

The alloy of a valve in a low-compression Continental engine is precisely the
same alloy as the 100LL exhaust valve. The 100LL valve has had some machine
work and clearance work (mainly in the stem area and in the angle of the valve
seat area) done to make it compatible with the excess 100LL lead that jams
valves.



->I don't know the answer but I tell you what I suspect. I suspect the egt
->of 100LL will be higher.

You suspect wrong. I have made this exact same measurement on several
low-compression Continentals before I started using mogas (primarily the O-300D,
but a couple of more engines to a lesser extent. Mogas burns hotter according
to the EGT.


->Higher octane gasoline like 100LL, furthermore, is a little less volatile
->than mogas and burns more slowly because of the higher RON numbers, so that
->when the exhaust valve opens combustion is less complete than with the same
->charge of mogas -- in the low-compression O-300. So if you're running
->100LL in an O-300-powered 172, why do you need 100-octane exhaust valves,
->whose faces are something like inconel or another exotic alloy designed for
->temperatures much higher than the stock exhaust valves?

You predicate your entire argument on the fallacy of "exotic alloy" valves, when
in fact, the only difference is in the settings of the lathe that cuts them.

Jim

Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com

[JFLEISC]

Before I would buy into any of this (this runs hotter/cooler than that) I would
like to see some kind of quantitative study, i.e. a quantity of different size
engines from the same manufacturer and then different manufacturers. Other
things also like what seasonal additives the mogas may or may not have. After
13 years of dynomometer testing on air cooled VW engines I have seen the same
motors react ever so slightly to things like different fuel, etc. due to things
like, for example, timing (ignition, valve, whatever) being a tick different.
What I'm saying is that one engine may seem to run hotter with a different fuel
while another may seem to run cooler with the same switch.

Jim

[jls]

"Jim Weir" > wrote in message
...
> " jls" >
> shared these priceless pearls of wisdom:
>
> ->
> ->And if the burn is cooler when 100LL (rather than 80) is run through the
> ->carb, why is it the engine must have special 100LL exhaust valves, which
are
> ->designed with high-temperature alloys?
>
> The alloy of a valve in a low-compression Continental engine is precisely
the
> same alloy as the 100LL exhaust valve. The 100LL valve has had some
machine
> work and clearance work (mainly in the stem area and in the angle of the
valve
> seat area) done to make it compatible with the excess 100LL lead that jams
> valves.

I stand corrected, then. Thanks for your lecture and I note that you
rubbed it in a little too. OK, all in a day's fun. I can take it.
<Sniffle> I had read that the 100 octane valve was a different alloy but
always wondered if it were so. It sure is a comparatively expensive little
bugger.
>
> ->I don't know the answer but I tell you what I suspect. I suspect the
egt
> ->of 100LL will be higher.
>
> You suspect wrong. I have made this exact same measurement on several
> low-compression Continentals before I started using mogas (primarily the
O-300D,
> but a couple of more engines to a lesser extent. Mogas burns hotter
according
> to the EGT.

Thanks. I will find out soon with respect to my own O-300 which will have
EGT sensors and will compare results. Btw I enjoyed the poke you took at
the poor guy who had chickens in his sparkplugs. He was right gentlemanly
about the poke too.
>
>
> ->Higher octane gasoline like 100LL, furthermore, is a little less
volatile
> ->than mogas and burns more slowly because of the higher RON numbers, so
that
> ->when the exhaust valve opens combustion is less complete than with the
same
> ->charge of mogas -- in the low-compression O-300. So if you're running
> ->100LL in an O-300-powered 172, why do you need 100-octane exhaust
valves,
> ->whose faces are something like inconel or another exotic alloy designed
for
> ->temperatures much higher than the stock exhaust valves?
>
> You predicate your entire argument on the fallacy of "exotic alloy"
valves, when
> in fact, the only difference is in the settings of the lathe that cuts
them.
>
> Jim
>
> Jim Weir (A&P/IA, CFI, & other good alphabet soup)
> VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
> http://www.rst-engr.com

[Stu Gotts]

On Mon, 08 Mar 2004 08:08:58 -0800, Jim Weir > wrote:

>Stu Gotts >
>shared these priceless pearls of wisdom:
>
>Now to the point -- I thought you said that your source had DONE the experiment
>and HAD data. People who have been there and done that don't say "SHOULD" and
>"PROBABLY", they say "DID". I think you've dicked the problem without hard
>data.
>
>
>Jim
>
I agree, but that's not in character for him. But if I may be so bold
to correct the Great Weir, "Shall" must be used rather than "Should".
You're a big boy, call him up and ask him. My "source" is George
Braly of GAMI. You know, injectors, turbo normalizing, PRISM, APS,
etc. He wrote it, he sent it, he answered it. You may be surprised
to hear how he arrived at the answers.

[Jim Weir]

I don't give a DAMN how he arrived at the answers other than doing the
experiment. Obviously he hasn't. I don't know what is in "character" for a
person of this magnitude other than to tell it right up front HOW he measured it
and under WHAT conditions. Then others can repeat the experiment and show it
valid or not.

Every scientist from the dawn of time through Newton and Einstein published
their theory, and then the proofs, and then the experiments to prove them right
or wrong. If Brother Braly isn't willing to give us hard numbers as to his
measurements, then we are just whistling in the wind.

Try again, and no, I'm not going to waste my time with phone calls. If the
"probably"s in this newsgroup were laid end to end, it would be a good idea.

Jim





Stu Gotts >
shared these priceless pearls of wisdom:

->On Mon, 08 Mar 2004 08:08:58 -0800, Jim Weir > wrote:
->
->>Stu Gotts >
->>shared these priceless pearls of wisdom:
->>
->>Now to the point -- I thought you said that your source had DONE the
experiment
->>and HAD data. People who have been there and done that don't say "SHOULD"
and
->>"PROBABLY", they say "DID". I think you've dicked the problem without hard
->>data.
->>
->>
->>Jim
->>
->I agree, but that's not in character for him. But if I may be so bold
->to correct the Great Weir, "Shall" must be used rather than "Should".
->You're a big boy, call him up and ask him. My "source" is George
->Braly of GAMI. You know, injectors, turbo normalizing, PRISM, APS,
->etc. He wrote it, he sent it, he answered it. You may be surprised
->to hear how he arrived at the answers.
->

Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com

[Stu Gotts]

Too bad your scope doesn't include an open mind and open ears. What
seems to be your problem? Something you can't claim to know anything
about? Poor baby!

For those that realize Weir can hurt as much as he helps (old age
assaholism, I guess, or maybe he's still ****ed that a foreigner could
beat him in the election), and would like to pursue this, a simple
email to George will give you any answers yo o may need to justify his
quiz Q & A's. I know the guy and his company and his work, and I'll
take him at his word. I'll drop him an email to see if he claims to
know anything about manufacturing electronics (other than the PRISM
system), but I somehow bet he'll leave that to the real experts in
the field without questioning them about what they eat for breakfast.

On Mon, 08 Mar 2004 19:47:05 -0800, Jim Weir > wrote:

>
>I don't give a DAMN how he arrived at the answers other than doing the
>experiment. Obviously he hasn't. I don't know what is in "character" for a
>person of this magnitude other than to tell it right up front HOW he measured it
>and under WHAT conditions. Then others can repeat the experiment and show it
>valid or not.
>
>Every scientist from the dawn of time through Newton and Einstein published
>their theory, and then the proofs, and then the experiments to prove them right
>or wrong. If Brother Braly isn't willing to give us hard numbers as to his
>measurements, then we are just whistling in the wind.
>
>Try again, and no, I'm not going to waste my time with phone calls. If the
>"probably"s in this newsgroup were laid end to end, it would be a good idea.
>
>Jim
>
>
>
>
>
>Stu Gotts >
>shared these priceless pearls of wisdom:
>
>->On Mon, 08 Mar 2004 08:08:58 -0800, Jim Weir > wrote:
>->
>->>Stu Gotts >
>->>shared these priceless pearls of wisdom:
>->>
>->>Now to the point -- I thought you said that your source had DONE the
>experiment
>->>and HAD data. People who have been there and done that don't say "SHOULD"
>and
>->>"PROBABLY", they say "DID". I think you've dicked the problem without hard
>->>data.
>->>
>->>
>->>Jim
>->>
>->I agree, but that's not in character for him. But if I may be so bold
>->to correct the Great Weir, "Shall" must be used rather than "Should".
>->You're a big boy, call him up and ask him. My "source" is George
>->Braly of GAMI. You know, injectors, turbo normalizing, PRISM, APS,
>->etc. He wrote it, he sent it, he answered it. You may be surprised
>->to hear how he arrived at the answers.
>->
>
>Jim Weir (A&P/IA, CFI, & other good alphabet soup)
>VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
>http://www.rst-engr.com

[jls]

"Jim Weir" > wrote in message
...
> " jls" >
> shared these priceless pearls of wisdom:
>
> ->
> ->And if the burn is cooler when 100LL (rather than 80) is run through the
> ->carb, why is it the engine must have special 100LL exhaust valves, which
are
> ->designed with high-temperature alloys?
>
> The alloy of a valve in a low-compression Continental engine is precisely
the
> same alloy as the 100LL exhaust valve. The 100LL valve has had some
machine
> work and clearance work (mainly in the stem area and in the angle of the
valve
> seat area) done to make it compatible with the excess 100LL lead that jams
> valves.

Now that I have done some homework, I find your statement here to be in
error. Please look up the alloy formula for stellite, which is the exotic
alloy coating on expensive 100-octane aircraft engine exhaust valves. I
bought several of these exhaust valves recently for a small Continental
engine. I had earlier told you that I stood corrected but now must refute
what you have said here after having studied your arguments and contentions.
As for most of the typical exhaust valve surface it is chromium-plated and
the stellite added to the 100-octane exhaust valve is plated onto the
seating face.
>
>
>
> ->I don't know the answer but I tell you what I suspect. I suspect the
egt
> ->of 100LL will be higher.
>
> You suspect wrong. I have made this exact same measurement on several
> low-compression Continentals before I started using mogas (primarily the
O-300D,
> but a couple of more engines to a lesser extent. Mogas burns hotter
according
> to the EGT.

Yes, then, a negligible number, like 9 degrees as stated by a later poster
flying an O-360 powered 172 with avgas in one tank and mogas in the other.
'Net homework also shows, as this poster found, a negligible increase in EGT
with mogas.

>
>
> ->Higher octane gasoline like 100LL, furthermore, is a little less
volatile
> ->than mogas and burns more slowly because of the higher RON numbers, so
that
> ->when the exhaust valve opens combustion is less complete than with the
same
> ->charge of mogas -- in the low-compression O-300. So if you're running
> ->100LL in an O-300-powered 172, why do you need 100-octane exhaust
valves,
> ->whose faces are something like inconel or another exotic alloy designed
for
> ->temperatures much higher than the stock exhaust valves?
>
> You predicate your entire argument on the fallacy of "exotic alloy"
valves, when
> in fact, the only difference is in the settings of the lathe that cuts
them.

I am afraid that the manifest weight of authority is against you and
completely refutes you on your contention here. I just looked up those
stellite constituents for the typical 100-octane stellite exhaust valves
sold for Continental engines. They are pretty exotic, as in: manganese,
molybdenum, chromium, silicon, nickel, and cobalt. That doesn't sound to
me like enhancing a steel valve with a lathe. That stellite stuff sounds
like "exotic alloy" hardening to me.

You do YOUR homework now, fella. I'll respect your authority on the issue
of radios and antennae, however. I have now retracted my earlier statement
admitting error and saying that I stood corrected. The floor is yours now
to resurrect your case, if that is possible.
>
> Jim
>
> Jim Weir (A&P/IA, CFI, & other good alphabet soup)
> VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
> http://www.rst-engr.com

[Jim Weir]

" jls" >
shared these priceless pearls of wisdom:

-
->
->Now that I have done some homework, I find your statement here to be in
->error. Please look up the alloy formula for stellite, which is the exotic
->alloy coating on expensive 100-octane aircraft engine exhaust valves.

I know well the formula for stellite. If you are nuts enough to buy stellite
faced valves, I know there are people willing to take your money. If you want a
plain-jane 100 octane valve, there are those, too. I can tell you that I've
done enough work inside Continental engines to understand the difference. Have
you?


->> You suspect wrong. I have made this exact same measurement on several
->> low-compression Continentals
->
->Yes, then, a negligible number, like 9 degrees as stated by a later poster
->flying an O-360 powered 172 with avgas in one tank and mogas in the other.
->'Net homework also shows, as this poster found, a negligible increase in EGT
->with mogas.

An O-360 is a Lycoming. I said NOTHING about Lycomings of any persuasion. Read
the post. And I can tell you that the EGT showed a perceptible rise. I never
thought to record it to make a point in the newsgroups.



->I am afraid that the manifest weight of authority is against you and
->completely refutes you on your contention here. I just looked up those
->stellite constituents for the typical 100-octane stellite exhaust valves
->sold for Continental engines.

There are people who will sell you gold-plated speaker wire for your stereo,
too, and some people flat out believe that it makes the music sound more mellow.
P.T. Barnum had it pretty well nailed.

Jim
Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com

[jls]

"Jim Weir" > wrote in message
...
> " jls" >
> shared these priceless pearls of wisdom:
>
> -
> ->
> ->Now that I have done some homework, I find your statement here to be in
> ->error. Please look up the alloy formula for stellite, which is the
exotic
> ->alloy coating on expensive 100-octane aircraft engine exhaust valves.
>
> I know well the formula for stellite. If you are nuts enough to buy
stellite
> faced valves, I know there are people willing to take your money. If you
want a
> plain-jane 100 octane valve, there are those, too. I can tell you that
I've
> done enough work inside Continental engines to understand the difference.
Have
> you?

Yes, several Continentals, Lycomings, and even worked on a Franklin. I'm
overhauling an O-300 at the time. The 629404 exhaust valves were about $60
last time I checked. And when I bought stellite valves for an A-65 which
I'm also rebuilding, there were 2 diffrent kinds of 100-octane valves and
the stellites were cheaper.
>
>

[[email protected]]

Gene Kearns > wrote:
: Having actually done this...... 1967 C172H w/ Lycoming O-360-A2A

I do this all the time. Takeoff tank has some (or all) 100LL, other tanks
100% autofuel... '69 PA-28-180 with Lycoming O-360-A4A

:>->>Ok... little MOGAS quiz for you.
:>->>
:>->>You run the Left tank dry and fill it up with premium unleaded car
:>->>gas.
:>->>

: Used Amoco Premium

Wilco/Hess 93 A.K.I. (R+M/2)

:>->>Right tank has 100LL.
:>->>
:>->>Takeoff on the RH tank and climb, level off, and set up the mixture
:>->>for
:>->>cruise flight. Either ROP or LOP. Your choice.
:>->>

: ROP by 75 degrees.

More or less peak EGT at 65% power

:>->>
:>->>THEN, you switch to the LEFT tank. You change nothing else.
:>->>
:>->>Later you download your JPI and plot the data.
:>->>
:>->>1 What is it going to show happened to the EGTs when you switched
:>->>tanks?
:>->>

: Increase of about 9 degrees.

Roughly the same... analog gauges so difficult to get too accurate

:>->>2 What is it going to show happened to the CHTS when you switched
:>->>tanks?
:>->>

: Nothing observable.

Ditto

:>->>3 (not in the JPI, but: ) What is the airspeed going to do? Increase?
:>->>Decrease? Stay the same?
:>->>

: No observable change.

Ditto

-Cory
--
************************************************** ***********************
* The prime directive of Linux: *
* - learn what you don't know, *
* - teach what you do. *
* (Just my 20 USm$) *
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