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Matt Dralle
Site Admin
Joined: 08 Nov 2005
Posts: 25858
Location: Livermore CA USA
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 Posted: Thu Jul 17, 2008 9:02 am Post subject: 10:1 Compression / IO-360 200 HP |
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Does anyone have any experience with 10:1 compression in a IO-360 200 HP engine?
* What are the down sides of running 10:1 in that engine?
* What is the HP gain?
* What is the impact to TBO?
* What is the impact to reliability?
If you've done it, would you do it again, or just go with the standard 8.7:1 compression?
Matt Dralle
RV-8 #82880
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pitts_pilot(at)bellsouth.
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| Posted: Thu Jul 17, 2008 11:51 am Post subject: 10:1 Compression / IO-360 200 HP |
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Matt, AFAIK, there are some performance gains and loss of auto fuel. I
have an O-360 (180HP) in my Pitts. It has the high lift helo cam, 8.7:1
pistons and is balanced. The PS5 carb has been modified by opening up
the jets. Supposedly it puts out 200 to 225 HP at 3000 RPM. I rev the
crap out of it (3300) when doing akro on 92 octane. If I run regular,
it'll ping when it gets hot. I know this doesn't answer your questions,
but it's a data point.
Linn
do not archive
Matt Dralle wrote:
| Quote: |
Does anyone have any experience with 10:1 compression in a IO-360 200 HP engine?
* What are the down sides of running 10:1 in that engine?
* What is the HP gain?
* What is the impact to TBO?
* What is the impact to reliability?
If you've done it, would you do it again, or just go with the standard 8.7:1 compression?
Matt Dralle
RV-8 #82880
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rv8tor(at)lazy8.net
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| Posted: Thu Jul 17, 2008 5:11 pm Post subject: 10:1 Compression / IO-360 200 HP |
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The down side is you have to feed it more gas down low. The up side is that
it is more efficient up high. A little more power both places.
HP gain is probably only a couple percent.
It may reduce your TBO if you run it hard a lot.
I haven't seen any reliability problems in 500 hours and 5 airventure cup
races (wide open for 2 hours at low altitude).
Really, it depends on what you are aiming for. If you are after every bit of
performance, then it is good. If you just want to bomb around in a great
airplane, I would stay with stock.
Maybe a better way to go is port and polish. Cheap, and no related problems,
just 3-4 extra HP per cylinder.
For the ultimate performance of course, you do both. For the very best MPG,
add Lightspeed ignition for high altitude cruising.
Best, John Huft race 18, "Nuisance"
--
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Kellym
Joined: 10 Jan 2006
Posts: 1705
Location: Sun Lakes AZ
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| Posted: Thu Jul 17, 2008 5:47 pm Post subject: 10:1 Compression / IO-360 200 HP |
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These pistons were designed for a helicopter version of the engine, and
Lycoming recommends NO leaning below something like 5 thousand or higher.
I know of one of these engines that self destructed in a Mooney, that
was being run with only stock instruments, so didn't see the high temps
on other cylinders.
Others report high oil consumption sometime after 500 hours. Have a
friend that is running them with no trouble, but keeps his temps down
and stays within the STC requirement on certified planes of no more than
28.5" MP.
Other downside is if 100LL ever gets reformulated to lower octane, you
will have problems or have to top the engine with lower compression pistons.
John Huft wrote:
[quote]
The down side is you have to feed it more gas down low. The up side is that
it is more efficient up high. A little more power both places.
HP gain is probably only a couple percent.
It may reduce your TBO if you run it hard a lot.
I haven't seen any reliability problems in 500 hours and 5 airventure cup
races (wide open for 2 hours at low altitude).
Really, it depends on what you are aiming for. If you are after every bit of
performance, then it is good. If you just want to bomb around in a great
airplane, I would stay with stock.
Maybe a better way to go is port and polish. Cheap, and no related problems,
just 3-4 extra HP per cylinder.
For the ultimate performance of course, you do both. For the very best MPG,
add Lightspeed ignition for high altitude cruising.
Best, John Huft race 18, "Nuisance"
--
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Kelly McMullen
A&P/IA, EAA Tech Counselor # 5286
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khorton01(at)rogers.com
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| Posted: Fri Jul 18, 2008 3:09 am Post subject: 10:1 Compression / IO-360 200 HP |
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On 17-Jul-08, at 12:55 , Matt Dralle wrote:
| Quote: |
Does anyone have any experience with 10:1 compression in a IO-360
200 HP engine?
* What is the HP gain?
|
An increase in compression ratio increases the thermal efficiency of
the engine - i.e. a higher percentage of the energy in the fuel is
converted to mechanical work.
http://www.popularhotrodding.com/tech/0311_phr_compression_ratio_tech/index.html
In theory, if you made no other changes to the engine, the power would
increase by 4%, which would probably yield about a 5% increase in rate
of climb and about a 1.3% increase in speed.
--
Kevin Horton RV-8 (final assemby)
Ottawa, Canada
http://www.kilohotel.com/rv8
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gmcjetpilot
Joined: 04 Nov 2006
Posts: 170
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| Posted: Fri Jul 18, 2008 8:48 am Post subject: 10:1 Compression / IO-360 200 HP |
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I have not done 10:1 on my RV but have some
experience with HC pistons on Lycs.
First Lyc engineers pretty much max out most Lycs at
8:50:1 or 8:75:1 because that is the highest reliable
compression with GOOD detonation margins.
Detonation can lead to valve, piston, rod or rod bearing
damage....total failure. That is a fact.
One big exception to the above are the O-235's at 9.70:1
CR. They where withdrawn from the market. They
where fine in the test cell, in service they where failing
in the hands of pilots. Although there are STC's to boost
the power of C-152's & Grumman Yankee's with 235's. I
worked on one of those STC's. We blew a piston during
FAA trials.
Why use HC pistons? In the example above going from
8:5:1 to 9.70:1 produced a HP increase from 118 HP to
125 HP, a gain of 7 HP. Not much.
Some Helicopter engines have 10.0:1. Look at the
NTSB accident reports and TBO for those aircraft. You
will be impressed on how often these HC piston
helicopter engines fail, total failure. I don't think newer
helicopters like the Robertson Helicopters run HC
piston engines (for a reason).
Gas in the future will not be 100LL. It's very likely we'll
get green Av-gas in the near future, likely called 95UL
or 92UL, which the Euro folks now have. This lower / no
lead gas will have less octane and thus will not be good
for HC (meaning it won't run safely). You can
retard timing to compensate for lower octane but there
goes your handful of extra ponies.
Bottom line - detonation margin is cut down drastically
with HC pistons. Detonation can happen with out being
noticed by pilot, very subtle, while causing damage and
eventually total engine failure. If you operate carefully
with full knowledge of how your engine works than it
can be done safely. Lyc has to make engines that will
work in all conditions with ham-handed pilots. 8.75 is a
reliable number.
My experience with the 9:7:1 STC on the O-235 Lyc
and the fear of detonation kept me from bumping up my
O-360 (180HP) up from the stock 8:5:1. I just don't need
the extra 4 or 6 HP.
I am using dual electronic ignition with timing advance.
To mix in HC pistons with timing advance is a bit of an
unknown, hit and miss guess. To compensate
people limit timing advance, arbitrarily. Less timing
advance less power and the "No Free Lunch Rule"
comes into play. You lose your HC pistion gain.
Lycs Key Reprints give several bullet points for max
engine life....... one being operate at 65% power. Well that
makes sense, 100% power the engine will not last as
long & wear faster. There is no doubt that higher
combustion pressures has Pros & Cons. The Pro is
more power and actually better SFC or efficiency. The
Con is you're running higher pressures & temps and
that affects all the parts in the engine.
If using a metal prop the affect on the props vibration
response & fatigue, a big unknown affect with HC pistions.
When you add up all the SHOULD and SHOULD NOT
.............. I think there are more on the NOT side.
4-into-1 exhaust, Electronic Ignition for hotter spark all
add HP & efficiency with out as much draw back as the
HC Piston. Also making the airframe less draggy with a
better cowl or wheel & gear fairings is the gift that
keeps on giving. No down side but better efficiency that
equals or exceeds the speed gain you would get by adding
twice the HP HC pistons would give you. Sure more
power is better for takeoff and climb but RV's already do
pretty good with out more HP.
Cheers Matt
George
>Time: 10:02:08 AM PST US
| Quote: | From: Matt Dralle <dralle(at)matronics.com>
Subject: 10:1 Compression / IO-360 200 HP
Does anyone have any experience with 10:1 compression in a IO-360 200
>HP engine?
|
| Quote: |
* What are the down sides of running 10:1 in that engine?
>* What is the HP gain?
|
| Quote: |
>* What is the impact to TBO?
|
| Quote: |
>* What is the impact to reliability?
|
| Quote: |
If you've done it, would you do it again, or just go with the standard
>8.7:1 compression?
|
| Quote: |
Matt Dralle
RV-8 #82880
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[quote][b]
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aerokinetic(at)sbcglobal.
Guest
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| Posted: Sat Jul 19, 2008 1:30 pm Post subject: 10:1 Compression / IO-360 200 HP |
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Interesting to follow this thread...
Especially since I just upped my compression in the RV-4 from 8.5:1 to 9.0:1 on my O-320.
My personal experiences would make me tend to agree with jetpilotgeorge. I can say that I detect no real differences in performance so far, and I have totally given up the option to run on lower-octane fuels. I'm strictly 100LL now. At 8.5 I found I could run most good-quality 87 octanes with no detonation. It was right near the limit with stuff in that octane range. I've fooled around with auto fuel for many years and while using an ANR headset I can hear (more like feel) the onset of detonation. George is correct -it's very subtle and difficult to detect unless it's really extreme detonation. Never hear it at all without the ANR cutting out all the rumble.
I just ran the numbers using the formula from the article cited by Kevin Horton earlier in this thread and found the efficiency increase gained by my doing this to be a whopping one to 1.5 percent or 2.4 horsepower at best... and all at the cost of longevity, reliability and the ability to run multiple (and less-expensive) fuels.
A bad decision I feel... and if it wasn't so darn much work, I'd take those pistons right back out today... and breathe easier. Big gains to be had going from 7.0:1 up to 8.5... just liabilities from 8.5 to 9.
All those people out there claiming they have such-and-such horsepower output from their engines are mostly just blowing smoke. You hear it at every fly-in or airport bull session. 99% have never run their engines on a dyno or otherwise demonstrated what power they are really making. Some friends of mine just had an O-320 built up with 9.0:1 pistons and cold-air induction and fuel injection at a reputable shop. It was actually run in a dyno-equipped test cell at Poplar Grove Airmotive. Made 168 horsepower. That's only 8 more than rated for an 8.5:1 O-320 with a carb and Lycoming's own stock (hot-air) sump. I'd be willing to bet serious money most of the gain is from the cold air alone and not from the compression -and the math confirms it.
A stock O-360 would have been a cheaper and more reliable horsepower upgrade -at the expense of some weight. Do your own math -lots of choices in this game... but that's what makes it so interesting.
Your mileage may vary.
Scott
N4ZW
[quote][b]
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