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911st 911st is offline
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Join Date: Jan 2004
Location: Sacramento
Posts: 7,269
There is a formula in Bruce Anderson's book on modifying Porsche's for computing approximate effective compression ratio of a motor on boost. For a supper charged motor with little or modest inter-cooling they suggest keeping the effective CR under about 11.6/1. It is interesting to me the factory on there NA 993's went to 11.3/1.

It comes out at the about the following limits.

6.5/1 at 1.2 bar
7/1 at 1.1 bar
7.5/1 at 1 bar
8/1 at .8 bar
9.5/1 at .45 bar

It may be possible to go past this with extra fuel, pulled back timming, and an extra efficient inter-cooler but I do not understand the principles yet???

Old 03-08-2009, 08:58 PM
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