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High Compression Pistons?

1flyingyogi

Well Known Member
I have an O-320 160hp engine on my RV4, 420 SMOH and am considering getting high compression pistons. Maybe 9.5:1?

I've heard mixed opinions - some say it'll cause problems and if I want reliability and no hassles, don't do it.

Others have said that's not true and they've done it and had no issues.

I'd like to hear from those who have done it and had a good or bad experience or those who have a lot of knowledge on this topic and clear things up for me.

Also maybe some advice on where to get this done. Any reputable shops in Socal?

Thanks!
 
I can provide a single data point. I recently purchased an RV-8 that has an IO-360 (really an O-360 A1A modified by Lycon before installation) that has, among other things, 10:1 pistons.

The person that I bought it from was concerned about not being able to make it to TBO because of the high compression pistons, but it currently has 1988 hrs on it and it runs like top. It still has good compressions, doesn't make ANY metal, and still runs strong a smooth. The only drawback is that it has fairly high oil consumption that has gradually increased over the past 5-7 years. It now eats one quart about every 4(ish) hours.

I plan to keep flying it for at least a few more years (maybe until they get the high octane unleaded fuel issue resolved [that was sarcasm, in case you missed it]).

I would recommend you "Make it so"!
 
My O-320-E3D has over 850 hrs. since installing 9.5:1 pistons.
No negative effects as yet. I DID install new Lycoming cylinders at the same time.
Burns about a quart every 12-14 hrs. of normal flying.
 
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Your call.

No problems with this, but it is your call and your type of flying that counts on this question. We run 9:1's with the power pulled back most of the time other than for take-off and higher flight levels. The extra pressure translated into a little more power is useful when wanted, however with a light aircraft you don't need it that much if you fly to get from one place to another. Sure if you are hammering 70% or more of the time you will want as much power as you can get out of a crack-case. That does cost more and does if you keep the hammer to it make the engines wear some what faster, with more heat and B.M.E.P. asked of it for more of the time that it is running. Its up to you as to what you want on this one. Even with very good servicing and tuning, what you ask of an engine and how long you run while asking it to produce and take that stress will set the clock on your power plants life cycle.
This may not help, but that's the way it has always been, long before me.
Yours, R.E.A. III # 80888
 
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No problems with this, but it is your call and your type of flying that counts on this question. We run 9:1's with the power pulled back most of the time other than for take-off and higher flight levels. The extra pressure translated into a little more power is useful when wanted, however with a light aircraft you don't need it that much if you fly to get from one place to another. Sure if you are hammering 70% or more of the time you will want as much power as you can get out of a crack-case. That does cost more and does if you keep the hammer to it make the engines wear some what faster, with more heat and B.M.E.P. asked of it for more of the time that it is running. Its up to you as to what you want on this one. Even with very good servicing and tuning, what you ask of an engine and how long you run while asking it to produce and take that stress will set the clock on your power plants life cycle.
This may not help, but that's the way it has always been, long before me.
Yours, R.E.A. III # 80888

I will concede there is a small increase in the work required for the compression stroke, but run appropriately LOP generating the same BMEP at an altitude (MAP) only (say 1000') lower is still within reasonable limits. Significantly higher CR's obviously ramp forces up a fair bit, and you may see a difference.
 
My original post was last year and now my cylinders are at Lycon for port/ flow balance. It's time to decide on pistons and I'm having a hard time deciding. Maybe some input from you guys can help me.

How much more HP can I expect out of 10:1 pistons? How about 9.5:1? I currently have 8.5:1.

I figure if it'll give me 8-10hp more, then it's worth it. If not, I'll stick to my stock pistons.

With higher compression pistons, Lycon recommends to have the cylinders coated with a ceramic/ polymer coating to keep temps down. This will cost an extra $360, plus cost of pistons. I will also have to send in my ECU to retard the timing (I have EFII electronic ignition). And retard my mag on the other side.

So for the extra cost and effort, will it be worth it??

Most of the performance increase will be in the port/ flow balance according to Lycon (about 20hp more).
 
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My original post was last year and now my cylinders are at Lycon for port/ flow balance. It's time to decide on pistons and I'm having a hard time deciding. Maybe some input from you guys can help me.

How much more HP can I expect out of 10:1 pistons? How about 9.5:1? I currently have 8.5:1.

I figure if it'll give me 8-10hp more, then it's worth it. If not, I'll stick to my stock pistons.

With higher compression pistons, Lycon recommends to have the cylinders coated with a ceramic/ polymer coating to keep temps down. This will cost an extra $360, plus cost of cylinders. I will also have to send in my ECU to retard the timing (I have EFII electronic ignition). And retard my mag on the other side.

So for the extra cost and effort, will it be worth it??

Most of the performance increase will be in the port/ flow balance according to Lycon (about 20hp more).

retarding the timing is likely to give back a good part of the power increase from the CR increase, at least during during peak or LOP operations, if you go that route. No sense spending the money and effort for a net push in cruise operations.
 
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Compression

0 320 with mags and 10-1 pistons on a non RV. I have tried 22 degrees and 25 degrees on the timing, cannot see any performance difference with the timing changes.
The 10-1 pistons allow the engine to produce 75% power at a higher altitude than with stock pistons.
 
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