Looking for facts about high compression pistons

Since I have to overhaul my O-360 engine I am trying to assess the
facts and old wive tales about using higher than 8.5:1 pistons. I am
not concerned about running autogas.

I fly at high altitudes. Usually 10500'-12,500' and up to 17,500'
when over the Rockies. My home airport is around 6,800' MSL with
density altitudes at take-off up to 10,000' in the summer.

My concern is whether up to 10:1 pistons reduces my expected TBO (2000
hours) or causes other problems.

Ron Lee

I do not have first hand experience, and there are probably very few people
who have a lot of first hand experience flying in your relatively high
altitude environment. However, quite a few of the folks in the RV community
who elected to go with high compression pistons in their engines will tell
you that they wouldn't do it again. Some report a rougher running engine,
most report a hotter running engine, and still others report starting
problems due to the higher compression making it harder to spin the engine.

And there are also plenty of folks who are happy with their high compression
choice...

Personally, I think you should talk with some shops who have experience in
this area. Lycon and Bart Lalonde (he runs an engine shop in Kamloops, BC)
come to mind. A google search should turn up phone numbers for both.

KB




"Ron Lee" wrote in message
...
Since I have to overhaul my O-360 engine I am trying to assess the
facts and old wive tales about using higher than 8.5:1 pistons. I am
not concerned about running autogas.

I fly at high altitudes. Usually 10500'-12,500' and up to 17,500'
when over the Rockies. My home airport is around 6,800' MSL with
density altitudes at take-off up to 10,000' in the summer.

My concern is whether up to 10:1 pistons reduces my expected TBO (2000
hours) or causes other problems.

Ron Lee

On May 31, 8:27 pm, "Kyle Boatright" wrote:
I do not have first hand experience, and there are probably very few people
who have a lot of first hand experience flying in your relatively high
altitude environment. However, quite a few of the folks in the RV community
who elected to go with high compression pistons in their engines will tell
you that they wouldn't do it again. Some report a rougher running engine,
most report a hotter running engine, and still others report starting
problems due to the higher compression making it harder to spin the engine.

And there are also plenty of folks who are happy with their high compression
choice...

Personally, I think you should talk with some shops who have experience in
this area. Lycon and Bart Lalonde (he runs an engine shop in Kamloops, BC)
come to mind. A google search should turn up phone numbers for both.

KB

"Ron Lee" wrote in message

...



Since I have to overhaul my O-360 engine I am trying to assess the
facts and old wive tales about using higher than 8.5:1 pistons. I am
not concerned about running autogas.

I fly at high altitudes. Usually 10500'-12,500' and up to 17,500'
when over the Rockies. My home airport is around 6,800' MSL with
density altitudes at take-off up to 10,000' in the summer.

My concern is whether up to 10:1 pistons reduces my expected TBO (2000
hours) or causes other problems.

Ron Lee- Hide quoted text -

- Show quoted text -

If you fly most of the time in high altitudes the higher compression
pistons will give you better performance. I am in the same boat here
in Jackson Hole Wy. My toy is sittin in the hangar at 6450 msl and I
always fly in the 11,000+ range. The only hiccup to higher comp
pistons is if you were to relocate down to sea level, then the motor
will be under some higher stresses, IMO the motor should live to TBO
though...

Ben
www.haaspowerair.com

If you fly most of the time in high altitudes the higher compression
pistons will give you better performance. I am in the same boat here
in Jackson Hole Wy. My toy is sittin in the hangar at 6450 msl and I
always fly in the 11,000+ range. The only hiccup to higher comp
pistons is if you were to relocate down to sea level, then the motor
will be under some higher stresses, IMO the motor should live to TBO
though...

Ben
www.haaspowerair.com

Thanks Kyle and Ben. Kyle, an important point is the altitude where I
fly which Ben's point covers. Last night I read a Sky Ranch article
and the stresses of a 10:1 piston may be problematic at sea level.
But I am rarely at an altitude and power seting where I even get 75%
power. So if that reduces the stresses from a 10:1 (or 9.5 to 1)
piston compared to sea level then it may be ok.

Obviously I am still trying to make a well informed decision.

Ron Lee

Check the Lycon site. Occasionally I hear rumors that they are working on
an STC for the IO540s in our Aztec. From what I understand, they would put
a red line on the MAP which should not be exceeded and this would protect
the engine from exceeding the HP rating. Like I said, this is simply hanger
talk but you may learn something from a phone call.
Jim

"Ron Lee" wrote in message
...
If you fly most of the time in high altitudes the higher compression
pistons will give you better performance. I am in the same boat here
in Jackson Hole Wy. My toy is sittin in the hangar at 6450 msl and I
always fly in the 11,000+ range. The only hiccup to higher comp
pistons is if you were to relocate down to sea level, then the motor
will be under some higher stresses, IMO the motor should live to TBO
though...

Ben
www.haaspowerair.com

Thanks Kyle and Ben. Kyle, an important point is the altitude where I
fly which Ben's point covers. Last night I read a Sky Ranch article
and the stresses of a 10:1 piston may be problematic at sea level.
But I am rarely at an altitude and power seting where I even get 75%
power. So if that reduces the stresses from a 10:1 (or 9.5 to 1)
piston compared to sea level then it may be ok.

Obviously I am still trying to make a well informed decision.

Ron Lee

"Jim Burns" wrote:

Check the Lycon site. Occasionally I hear rumors that they are working on
an STC for the IO540s in our Aztec. From what I understand, they would put
a red line on the MAP which should not be exceeded and this would protect
the engine from exceeding the HP rating. Like I said, this is simply hanger
talk but you may learn something from a phone call.
Jim

Thanks Jim, that was my view. Just don't use full throttle near sea
level. I can live with that trivial operational restriction.

Ron Lee

Also take a look at Lycomings Tech article titled "Look What They're Doing
To Our Engines". It gives their point of view, which as expected is don't do
anything that they haven't approved.

I'm sure Lycon will be at OSH. They are always well represented via the
airshow performers and play well to their target audience.

Jim

"Ron Lee" wrote in message
...
"Jim Burns" wrote:

Check the Lycon site. Occasionally I hear rumors that they are working
on
an STC for the IO540s in our Aztec. From what I understand, they would
put
a red line on the MAP which should not be exceeded and this would protect
the engine from exceeding the HP rating. Like I said, this is simply
hanger
talk but you may learn something from a phone call.
Jim

Thanks Jim, that was my view. Just don't use full throttle near sea
level. I can live with that trivial operational restriction.

Ron Lee