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spence88mph spence88mph is offline
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Join Date: Jan 2007
Location: Melbourne, Australia
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Originally Posted by 911st View Post
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.
They seem to hold together at .7 bar, the great thing is it's no slower than a stock carrera, you still have the 200 odd horse before boost, I think a 930 has something like 140hp off boost? Plus the higher gearing of the 915 or G50 and you have a much more drivable car in my opinion, not 930 bashing at all they are still my all time favorite car. My next step is to goto 8:1 but I fear the lose of that all round drivability but the 485hp (protomotive quotes at .85bar) will surely make up for it!

That RUF conversion looks very nice, looks very factory. I need to hunt a 965 intercooler down.
'89 911 M491+Turbo
'89 944 Turbo
'88 928S4
'18 C63S Coupe
Old 05-05-2010, 03:50 PM
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