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911st 911st is offline
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Join Date: Jan 2004
Location: Sacramento
Posts: 7,269
Porsche ran .8 bar with 7/1 compression for an on boost compression ratio of about 10.2. on the 930's.

Latter they ran 8/1 with .7 bar for a net of about 11.8/1 on the 944 turbo and 993TT.

A modded 930 seems ok with 7/1 CR running 1 bar at about 11/1 on boost compression.

I am sometimes wonder about the low pressure builds being on the aggressive side.

.5 to .7 bar on a stock Carrera's 9.5/1 is a net of about 11.5/1 to 12.3/1 on boost compression ratio.

To stay under 11/1 net compression one would have to keep boost down to 5.5 psi. or .37 bar. To maintain a stock 930's CR the boost would have to limit boost to about 2.6 psi or 1.8 bar.

However, it seems to work well. Later stock normally aspirated Porsche's run up to 13.2/1 with knock sensing and twin plugs and some of them even seem to be able to run low boost on top of that.

My only guess is it is the lower intake temps that come with a low boost operation and very good tunning is what makes this possable.
Old 05-05-2010, 06:43 AM
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