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.

trent wrote:

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.



Were any of these 12:1 + engines air-cooled sporting carbs and fixed
advance ignition systems? Were they operated at 70% of peak for hours
at a time? I remember wasting all sorts of time looking for real
premium back in the early eighties for my watercooled V8 that ran 12.5:1
compression (without which it would sound like a paint can full of
marbles if I stayed on it too long). As regards the question at hand,
Lycoming deemed it necessary to upgrade the bottom end and the jugs on
the 0-320 when they pushed the compression up a point and a half, Pitts
is considering pushing it three points, which is definitely going to
increase the peak cylinder pressures and the bearing loads. Looking
through the Aircraft Engines of the World for several years in 1950s and
1960s, the highest compression engines I see are 8.7:1. Somehow I
recall a Lycoming helicopter engines did use a 10:1 ratio, but I can't
come up with a reference.


Charles

Charles Vincent wrote:
trent wrote:

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.


Were any of these 12:1 + engines air-cooled sporting carbs and fixed
advance ignition systems? Were they operated at 70% of peak for hours
at a time? I remember wasting all sorts of time looking for real
premium back in the early eighties for my watercooled V8 that ran 12.5:1
compression (without which it would sound like a paint can full of
marbles if I stayed on it too long). As regards the question at hand,
Lycoming deemed it necessary to upgrade the bottom end and the jugs on
the 0-320 when they pushed the compression up a point and a half, Pitts
is considering pushing it three points, which is definitely going to
increase the peak cylinder pressures and the bearing loads. Looking
through the Aircraft Engines of the World for several years in 1950s and
1960s, the highest compression engines I see are 8.7:1. Somehow I
recall a Lycoming helicopter engines did use a 10:1 ratio, but I can't
come up with a reference.


Charles

Found the reference -- it was the HIO-360, a beefed up version of the
IO-360 that had 10:1 ratio. The IO-360 had very different heads than
the O-360 (and 0-320)that would make it more resistant to detonation.
It seems there are examples of the IO-360 flying with 10:1 compression
pistons.

Charles

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