| Craig,
I believe GAMI puts the HP difference in the 5-7% range between at 7.5:1 and a 8.5:1. I've never been able to get more out of them than "it's diminishing returns" for higher than 8.5:1.
That said, there's another advantage to higher compression in turbo'd engine and that is that the turbine inlet temperature will be lower at a given power setting with the higher compression engine. In my installation, TIT is the limiting factor to how rich I can take the mixture when LOP. (I have a 7.5:1 engine).
So if I had a turbo and I was doing the engine from scratch, I would definitely get at least 8.5:1. If I didn't have a turbo I would say the advantage is marginal.
I also wouldn't own a 10:1 engine or any turbo engine without going to APS.
Colyn
On Nov 12, 2010, at 7:33 AM, Craig Jimenez wrote: What's the group's general opinion about 10:1 compression? I like the idea (higher efficiency). I found that raising the compression on my old Grumman AA5 from 7.x to 8.5 vastly improved the climb and high altitude performance. I'd be interested in your practical experiences of going to 9 or 10:1.
If I understood correctly, when running LOP, you can expect more power for any fuel flow at higher compressions:
Comp HP/gph
7.5 12.7
8.5 13.9
9.0 ?
10.0 ?
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