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turboteener turboteener is offline
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Join Date: Jan 2002
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I don't think there really is a relationship. Every engine will be different in what it wants as far as cylinder pressure rise and the resulting HP. I doubt you could lay out some hard ground rules as far as this boost and this compression ratio equal this HP.

Years ago I ask the question: "Would an engine with low compression and high boost make more power than an engine with high compression and low boost"? Well I got a million different answers and none of them really correct. It all depends on the application. I can take a modern pentroof four valve engine and run 11.5 with 10lbs and get excellent drivability, power and efficiency, but I would imagine that same engine running 9.0 would take more boost to make the same level of HP, thus adding more heat to the combustion cycle. It would be interesting to test it. Now with a 911 engine it will be a vastly different situation. The poor combustion chamber design and the aircooling/oilcooling require another approach. If I can get some time maybe I can build a motor with 10.0 and one with 7.0 and see what the differences would be. It would just be a matter of changing pistons. Leave everything else the same. Obviously it wouldn't be optimized for each condition, but it would be an interesting test.

One thing that would really affect the results of the test would be the usage of the engine. A street motor with limited track use, would be better with the higher compression, but the race motor would probably work better with lower compression since your turbo would remain spooled most of the time and you wouldn't have to worry about poor drivability outside of turbo.

Sorry I ramble.
Old 03-09-2008, 07:31 AM
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