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Dutch924-racer · Joined: 23 Jul 2007 Posts: 1081 Location: The Netherlands

I am building a new engine for my 931 track car

Setup:
Integral stage 1 cam + uprated valve springs
937 DITC
Stock CIS
Dansk Exhaust
GT style top mount intercooler (slightly thicker then original), later I will go for 951 front mount.
large oil cooler
951 250hp K26/8 turbo watercooled

I have the choice of two set of pistons, 7,5:1 or 8,5:1

I want to go more for reliability rather then getting the max hp out of the engine.

What will be better:
- run the 7,5:1 high boost, 1 bar?
- run the 8,5:1 at lower boost, 0.85 bar?
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937 trackday car
Series 2 engine
951S turbo and intercooler
Fast road camshaft
Forge recirculation valve + boost controller

gegge · Joined: 27 Jul 2007 Posts: 1124 Location: Sweden

The stage 1 cam will give you a lower dynamic compression, guessing 0,5 lower than the stock cam. The boostlevel is low enough to run the highcomp set.

But the the lowcomp highboost combo will give slightly more power, be more detonation tolerant and be able to run more aggresive ignition as well as higher boost.
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Carl Fredrik Torkildsen

924 turbo -81 Carrera GT RESTOMOD
924 turbo -80 Dolomite De Luxe
924 -85 DP kit, BBS RS, M030 and tuned engine
924s -86 Black on black turbo with Fuchs

Dutch924-racer · Joined: 23 Jul 2007 Posts: 1081 Location: The Netherlands

Do you know about how much horsepower I can count with these setups ?
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937 trackday car
Series 2 engine
951S turbo and intercooler
Fast road camshaft
Forge recirculation valve + boost controller

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

I'm enjoying high comp and low (10 -12 PSI) boost.
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Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

flosho · Posted: Tue Aug 09, 2011 6:33 am Post subject:

I'd go for the higher CR.
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[This Space For Rent]

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

I concur with the higher CR / lower boost combination. Think thermal management.

FWIW, on the "long-rod" engine I've just installed into the 941, I'm running 8.7:1 CR (and that's even after adding a thicker Cometic head gasket), along with an S1 turbo / wastegate combo, which appears to be putting out ~10 psi. So far, no pinging, but I haven't finished breaking in the motor.
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erstwhile owner of just about every 924 variant ever made