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10:1 IO-540 - Your Personal Experiences?

Dad's RV-10

Well Known Member
My RV-10 will have dual P-mags and Airflow Systems air conditioning. It will be based in Florida.

The engine is at a well known & reputable shop for IRAN and we're discussing boosting the power/compression a bit.

If choosing to go 9:1, they will use Lycoming pistons. If choosing 10:1, the pistons will be from Combustion Technologies.

I'm curious to hear from those with actual experience running IO-540's with increased compression.

Thanks.
 
10:1

I know you are waiting to hear from pilots using a 10:1 compression ratio and
I am sure they will pipe up before too long.
No one can argue the very slight increase in efficiency but I would like to offer you a better alternative.
Why not change to 8.5 : 1 instead? This change will open up opportunities for lower octane gasoline including 91E10 and other non leaded products.
10:1 will lock you into 100LL and nothing else albeit at a slightly reduced fuel consumption.
Here in the progressive west we are beginning to see 100LL disappear due to litigation surrounding lead contamination.
Think about it.
 
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Big compression is more easily managed with a tunable ignition advance curve. Keeping detonation at bay requires a substantial timing retard at TO power, but this will conflict with the still fairly high advance number at LOP. Not many ignitions allow this broad range. Might rethink the Pmag and look to SDS.
 
I think the continued availability of 100LL should be an important consideration

+1.
This is reason why I ordered my new Cold Air Sump IO-540 with standard 8.5 pistons. The gain in engine efficiency going to 9 or 10 pistons is in the grass when you overlay projected avgas cost.

I suspect the way the DC crowd is going we will all be looking for alternatives to 100LL or the yet to be provided 100UL novelty fuel.

Carl
 
Put me in the camp of enjoying more power today with 9.6 and mags.
I'll worry about 100LL going away later (they were saying the same thing 20yrs ago).
At this point I'll probably be gone from this world before 100LL is. :D
 
Put me in the camp of enjoying more power today with 9.6 and mags.
I'll worry about 100LL going away later (they were saying the same thing 20yrs ago).
At this point I'll probably be gone from this world before 100LL is. :D

That's true enough Walt - but I'm burning 93E10 that I'm buying at sub-$5 prices. Compared to 7 and 8 dollar avgas at most airports, that becomes downright attractive. You're not going to do that on 9:1 or 10:1 compression.

$2 per gallon saved, on 8 gph, x 2000 hours, is $32,000 saved in fuel alone just in one TBO. I'll gladly sacrifice a couple knots of top end performance for that.

I only paid $25k for the engine in the first place, and at 1100 hours now I'm quickly sneaking up on saving as much as I paid. When it's time for a top overhaul I'll go back on with ported/polished/flowmatched cylinders - but I'm keeping the compression right where it is.
 
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I'll toss this in. Although my knowledge of engines is admittedly far less than many here, my concerns about 100LL vs auto fuel are of a somewhat different nature than cost or availability.

I'd suspect that for most builders/flyers of the RV-10, the main use for the airplane is a long hauler for cross country trips, often IFR, at higher altitudes and long legs. That's at least my intent in building one.

I read a lot here about people using mogas in their RVs, but where I live, and where I fly, mogas is pretty much completely unavailable, or at least not economically competitive. I've never seen mogas on offer at airports I have visited, so I'd need to be bringing it in drums or flying long distances to get it. Around here, ethanol free gasoline at 93-94 octane is quite expensive, close to equivalent to 100LL in price. For long cross countries, you have to be assured that your chosen fuel will be available.

My understanding is that vapor pressure and absorbed moisture issues with auto fuel also make it undesirable for higher altitudes and very low temperatures.

The higher efficiency available at higher compression ratios might be more appropriate for extending range/endurance than for reducing cost. More range and endurance would always be useful for my assumed RV-10 mission. Burning cheaper fuel at a higher rate would be counterproductive in that case.
 
That's true enough Walt - but I'm burning 93E10 that I'm buying at sub-$5 prices. Compared to 7 and 8 dollar avgas at most airports, that becomes downright attractive. You're not going to do that on 9:1 or 10:1 compression.

$2 per gallon saved, on 8 gph, x 2000 hours, is $32,000 saved in fuel alone just in one TBO. I'll gladly sacrifice a couple knots of top end performance for that.

I only paid $25k for the engine in the first place, and at 1100 hours now I'm quickly sneaking up on saving as much as I paid. When it's time for a top overhaul I'll go back on with ported/polished/flowmatched cylinders - but I'm keeping the compression right where it is.

What altitudes are you flying that 93E10? Do you find any altitude/temperature concerns with it? Here at our airport, the only way to get that in our airplanes would be to tanker it on site, or find it at other local airports, but AFAIK, none of our local fields have it either.
 
What altitudes are you flying that 93E10? Do you find any altitude/temperature concerns with it? Here at our airport, the only way to get that in our airplanes would be to tanker it on site, or find it at other local airports, but AFAIK, none of our local fields have it either.

I routinely fly in the 14k-17k range where my efficiency curve peaks, and I've had it up to FL190 several times and FL210 twice. I am running the SDS system, so my fuel rail runs at 44 psig out of the fuel pumps, enough to remove any concerns of vapor lock, even at altitude.

I am on a private strip, 32 nautical miles from the nearest "real" airport, so I have my own fuel here. I bought a 125 gallon stainless steel chemical tank and put it in a 275-gallon "plastic tote" frame, so I can just forklift it into the back of my pickup and take it to town for a fillup when needed. I burn WalMart-grade auto premium with ethanol, last tank full was $4.92 per gallon. And yes, I literally buy it at Walmart - because they have the cheapest fuel price around, and move enough product that I don't have to worry about it getting old in the tanks.

On the road I just buy as much 100LL as I need to get back - it will mix and run just fine of course. I have long range tanks on my 9A and carry a total of 67 gallons, so I can tanker fuel out with me and avoid buying 100LL entirely for most trips, or at least minimize it.
 

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I routinely fly in the 14k-17k range where my efficiency curve peaks, and I've had it up to FL190 several times and FL210 twice. I am running the SDS system, so my fuel rail runs at 44 psig out of the fuel pumps, enough to remove any concerns of vapor lock, even at altitude.

I am on a private strip, 32 nautical miles from the nearest "real" airport, so I have my own fuel here. I bought a 125 gallon stainless steel chemical tank and put it in a 275-gallon "plastic tote" frame, so I can just forklift it into the back of my pickup and take it to town for a fillup when needed. I burn WalMart-grade auto premium with ethanol, last tank full was $4.92 per gallon. And yes, I literally buy it at Walmart - because they have the cheapest fuel price around, and move enough product that I don't have to worry about it getting old in the tanks.

On the road I just buy as much 100LL as I need to get back - it will mix and run just fine of course. I have long range tanks on my 9A and carry a total of 67 gallons, so I can tanker fuel out with me and avoid buying 100LL entirely for most trips, or at least minimize it.

Thanks! Very interesting. My -10 will have the Airflow Performance fuel injection that the engine came with, but I'm planning on the SDS CPI-2 ignition.

Have you ever had any indication of ice formation in the fuel? Any special things you had to do to the fuel system to deal with ethanol?
 
Thanks! Very interesting. My -10 will have the Airflow Performance fuel injection that the engine came with, but I'm planning on the SDS CPI-2 ignition.

Have you ever had any indication of ice formation in the fuel? Any special things you had to do to the fuel system to deal with ethanol?

I've never had any indication of ice in the fuel, no. That's a whole 'nuther discussion, not for this thread.

I removed all rubber components from the entire fuel system and replaced them all with viton or teflon materials, and of course removed the engine-driven fuel pump and replaced it with dual electrics. I actually did that on the original build - using the stock Bendix injection setup and running about 35 psig fuel pressure, with return line back to the tanks. The standard fuel injection servo is good for 40 psig and it worked quite well that way for almost 600 hours before I installed the full SDS system.
 
I know you are waiting to hear from pilots using a 10:1 compression ratio and
I am sure they will pipe up before too long.
No one can argue the very slight increase in efficiency but I would like to offer you a better alternative.
Why not change to 8.5 : 1 instead? This change will open up opportunities for lower octane gasoline including 91E10 and other non leaded products.
10:1 will lock you into 100LL and nothing else albeit at a slightly reduced fuel consumption.
Here in the progressive west we are beginning to see 100LL disappear due to litigation surrounding lead contamination.
Think about it.

My Own opinion is based on 12 years of living with a 10:1 IO 540 in a rocket.
Short story is that 10:1 is a PITA
Not quite so much that I have sent it away for OH but if and when the day comes, it WILL have 8.5:1 CR when I put it back in the air. 10:1 is fine provided you have absolutely fresh LL100 fuel at your airport. We don't as there are 2 underground tanks that only get drawn down to about 40% capacity , then they switch to the other tank/ pump , leaving the other side to get old and stale for as long as a year before they take a fresh load that gets diluted with the old gas. And that is with only 19-20 deg advance. Methanol water injection that comes on at about 21" MP will allow full power for as long as you have 50%/50%methanol / water mix (spraying into the air intake) to feed it at about 10% of the volume that the LL100 is being consumed at when it starts at 21"MP and increase the volume to 25-30% of the LL100 consumption by 27" MP.

I fly a second IO 540 with 8.5:1 and no matter where I have filled with fuel, Full power take offs and climbs are a non issue. 25 deg advance as per the mark plate. Just fly it. No issues.

If you had 2 rockets taking off , one with 8:5:1 and the other with 10:1 I doubt you would be able to tell which one had what engine. Unless you had older fuel in both, in which case the 8.5 :1 will pull ahead from the poor soul in the 10:1 as he reduces power at the fist tones or hint of pre ignition.

10:1 is fine if you have fresh LL100, new spark pugs, verify perfect timing and have a perfect battery, solenoids and cables to crank the beast.

If you like to tinker and mess around and spend realms of money then 10:1 will do it for you.

If on the other hand you like to fly a lot then 8.5:1 or perhaps 9:1 will do that for you.


YMMV
 
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Put me in the camp of enjoying more power today with 9.6 and mags.
I'll worry about 100LL going away later (they were saying the same thing 20yrs ago).
At this point I'll probably be gone from this world before 100LL is. :D

And 20 yrs before that.
 
odd...

My Own opinion is based on 12 years of living with a 10:1 IO 540 in a rocket.
Short story is that 10:1 is a PITA Not so much that I have sent it away for OH but if and when the day comes, it WILL have 8.5:1 CR when I put it back in the air. 10:1 is fine provided you have absolutely fresh LL100 fuel at your airport. We don't as there are 2 underground tanks that only get drawn down to about 40% capacity , then they switch to the other tank/ pump , leaving the other side to get old and stale for as long as a year before they take a fresh load that gets diluted with the old gas. And that is with only 19-20 deg advance. Methanol water injection that comes on at about 21" MP will allow full power for as long as you have 50%/50%methanol / water mix to feed it at about 10% of the volume that the LL100 is being consumed at.

I fly a second IO 540 with 8.5:1 and no matter where I have filled Full power take offs and climbs are a non issue. 25 deg advance as per the mark plate. Just fly it. No issues.

If you had 2 rockets taking off , one with 8:5:1 and the other with 10:1 I doubt you would be able to tell which one had what engine. Unless you had older fuel in both, in which case the 8.5 :1 will pull ahead from the poor soul in the 10:1 as he reduces power at the fist tones or hint of pre ignition.

10:1 is fine if you have fresh LL100, new spark pugs, verify perfect timing and have a perfect battery, solenoids and cables to crank the beast.

If you like to tinker and mess around and spend realms of money then 10:1 will do it for you.

If on the other hand you like to fly a lot then 8.5:1 or perhaps 9:1 will do that for you.


YMMV

I have a friend with an RV-10 that has a 10:1 Thunderbolt 540 with CAI and EFII an it runs just fine...only complaint is, like you said, cranking the beast...
 
My Own opinion is based on 12 years of living with a 10:1 IO 540 in a rocket.
Short story is that 10:1 is a PITA Not so much that I have sent it away for OH but if and when the day comes, it WILL have 8.5:1 CR when I put it back in the air. 10:1 is fine provided you have absolutely fresh LL100 fuel at your airport. We don't as there are 2 underground tanks that only get drawn down to about 40% capacity , then they switch to the other tank/ pump , leaving the other side to get old and stale for as long as a year before they take a fresh load that gets diluted with the old gas. And that is with only 19-20 deg advance. Methanol water injection that comes on at about 21" MP will allow full power for as long as you have 50%/50%methanol / water mix to feed it at about 10% of the volume that the LL100 is being consumed at.

I fly a second IO 540 with 8.5:1 and no matter where I have filled Full power take offs and climbs are a non issue. 25 deg advance as per the mark plate. Just fly it. No issues.

If you had 2 rockets taking off , one with 8:5:1 and the other with 10:1 I doubt you would be able to tell which one had what engine. Unless you had older fuel in both, in which case the 8.5 :1 will pull ahead from the poor soul in the 10:1 as he reduces power at the fist tones or hint of pre ignition.

10:1 is fine if you have fresh LL100, new spark pugs, verify perfect timing and have a perfect battery, solenoids and cables to crank the beast.

If you like to tinker and mess around and spend realms of money then 10:1 will do it for you.

If on the other hand you like to fly a lot then 8.5:1 or perhaps 9:1 will do that for you.


YMMV

I think you may have something else going on with your engine besides the 10 to 1 pistons. I ran 10 to 1 on my prior aircraft with no issues like that. Currently running 9.5 to 1 and again have zero issues with timing currently fixed at 23. I would look carefully at your fuel system and flow rates.
 
I think you may have something else going on with your engine besides the 10 to 1 pistons. I ran 10 to 1 on my prior aircraft with no issues like that. Currently running 9.5 to 1 and again have zero issues with timing currently fixed at 23. I would look carefully at your fuel system and flow rates.

I appreciate that. After filling at an airport that has recently taken a load of fresh LL100 I can go to 27" with no water /methanol and have no issues.

As soon as I fill one side with the old fuel at home I can't go past 21" without the spray on.

I have repeated the experiment several times over the years.
Part of the issue is that in cruise my CHT's are only 270-302F ( 2 different brands of engine monitors and 2 different brands of probes used confirm the temps)and that makes for lead deposits, which make for hot spots , which in turn contribute to pre ignition unless you cool the combustion with the water spray and clean out the deposits at the same time.
 
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