High compresstion in O-320

Has anyone here done or considered 10:1 pistons for an E-series O-320.
I have read the articles on how an E series differs from the others, but
I am not sure that this closes the door on the subject.

For example, if one was mostly interested in takeoff power or power at
altitude...

I am sure it will bring down the TBO, but I don't expect to pass TBO on
the engine anyway (due to years more than wear). Besides, how many
homebuilts do? (I doubt there is a statistically significant group with
2000 hrs on them)

Mike

pittss1c wrote:
Has anyone here done or considered 10:1 pistons for an E-series O-320.
I have read the articles on how an E series differs from the others, but
I am not sure that this closes the door on the subject.
/snip/

Pitts,

I don't know all the details, but I do know the "E" series 320's have a
lighter duty front main bearing setup, as compared to the "D" models
that came with higher horsepower ratings. However, I can't say whether
the difference is that critical. How much HP do you suppose 10:1's
would produce? If you limited your takeoff MP to a degree, and just
used the extra efficiency at altitude, I can't imagine any harm being
done, at all.

Happy Flying!
Scott Skylane

Scott Skylane wrote:
pittss1c wrote:
Has anyone here done or considered 10:1 pistons for an E-series O-320.
I have read the articles on how an E series differs from the others,
but I am not sure that this closes the door on the subject.
/snip/

Pitts,

I don't know all the details, but I do know the "E" series 320's have a
lighter duty front main bearing setup, as compared to the "D" models
that came with higher horsepower ratings. However, I can't say whether
the difference is that critical. How much HP do you suppose 10:1's
would produce? If you limited your takeoff MP to a degree, and just
used the extra efficiency at altitude, I can't imagine any harm being
done, at all.

Happy Flying!
Scott Skylane
I believe changing from 7:1 to 8.5:1 gives you 10 HP
I would hope for something like a 15 to 25 hp improvement over the 7:1.

On Apr 19, 4:10 pm, pittss1c wrote:


I believe changing from 7:1 to 8.5:1 gives you 10 HP
I would hope for something like a 15 to 25 hp improvement over the 7:1.- Hide quoted text -

- Show quoted text -

Detonation will be the biggest limiting factor. At 10:1
100LL or even straight 100 probably won't cut it. There used to be a
115/145 fuel (purple) for the old high-output engines used in piston-
pounder airliners and so on. Dunno if it's available anymore, but the
guys who use old airliners for firebombing might know.
If you get detonation in an O-320, that engine won't last long at
all. You'll either burn holes in the pistons or blow the heads off the
cylinders. Cylinder bases have also been noted to pull right off the
case.

Dan

wrote:
On Apr 19, 4:10 pm, pittss1c wrote:

I believe changing from 7:1 to 8.5:1 gives you 10 HP
I would hope for something like a 15 to 25 hp improvement over the 7:1.- Hide quoted text -

- Show quoted text -

Detonation will be the biggest limiting factor. At 10:1
100LL or even straight 100 probably won't cut it. There used to be a
115/145 fuel (purple) for the old high-output engines used in piston-
pounder airliners and so on. Dunno if it's available anymore, but the
guys who use old airliners for firebombing might know.
If you get detonation in an O-320, that engine won't last long at
all. You'll either burn holes in the pistons or blow the heads off the
cylinders. Cylinder bases have also been noted to pull right off the
case.

Dan

I think people still use 100LL even with 12:1... I am going to be
surprised it 10:1 is an issue.

pittss1c wrote:

I think people still use 100LL even with 12:1... I am going to be
surprised it 10:1 is an issue.

The 8.5 to 1 jugs were designed with adequate detonation margins using the
old 91/96 octane blue gas. Logic would tell us that you should be able to go
with higher compression using 100LL, but I don't know of any version of the O-
320 where that has actually been tested, so the question of how much over 8.5
to 1 is adequate, remains a mystery.

Good luck.

John Galban=====N4BQ (PA28-180)

--
Message posted via AviationKB.com
http://www.aviationkb.com/Uwe/Forums...built/200704/1

"pittss1c" wrote in message
...
wrote:
On Apr 19, 4:10 pm, pittss1c wrote:


If you get detonation in an O-320, that engine won't last long at
all. You'll either burn holes in the pistons or blow the heads off the
cylinders. Cylinder bases have also been noted to pull right off the
case.

Dan

I think people still use 100LL even with 12:1... I am going to be
surprised it 10:1 is an issue.


It's not all down to compression ratio. Modern cars and motorcycles are
managing compressions over 12:1 with regular gas and very lean mixtures. The
design of the combusion chamber has a great deal to do with detonation. Get
some time with a design team and a computer model of your flame front and
you'll be fine.

I've heard reports of 0320s in NZ modified with 10:1 pistons in a helicopter
operation.
"pittss1c" wrote in message
...
Has anyone here done or considered 10:1 pistons for an E-series O-320.
I have read the articles on how an E series differs from the others, but I
am not sure that this closes the door on the subject.

For example, if one was mostly interested in takeoff power or power at
altitude...

I am sure it will bring down the TBO, but I don't expect to pass TBO on
the engine anyway (due to years more than wear). Besides, how many
homebuilts do? (I doubt there is a statistically significant group with
2000 hrs on them)

Mike