Compression stroke PSI
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Joined: May 2009
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From: Far West
Car: 1986 Camaro Z28 IROC-Z
Engine: 350 Tuned Port Injection, for now.
Transmission: 700R4
Axle/Gears: Posi - 3.23
Compression stroke PSI
Out of couriosity, what is the PSI in a cylinder just before ignition?
Joined: Apr 2005
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From: Not in Kansas anymore
Car: 82 Z28
Engine: 383 SP EFI/ 4150 TB
Transmission: T400
Axle/Gears: QP 9" 3.73
Re: Compression stroke PSI
Varies with the CR of engine
http://en.wikipedia.org/wiki/Compres...pressure_ratio
http://en.wikipedia.org/wiki/Compres...pressure_ratio
http://en.wikipedia.org/wiki/Compres...pressure_ratio
http://en.wikipedia.org/wiki/Compres...pressure_ratio
Supreme Member
Joined: Sep 1999
Posts: 7,072
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From: Philly, PA
Re: Compression stroke PSI
Also varies with WHEN the spark happens. If you run a compression test on your engine you'll probably find it reads about 160 PSI or so. But that's the PEAK reading (at TDC) with no spark present. Since the spark fires BEFORE TDC by some number of degrees the cylinder pressure would be less than that- maybe 100 PSI (guessing). When the motor is actually running (combustion is taking place) peak cylinder pressures usually happen around 15* AFTER TDC (if the timing is close to optimum) and they're much higher than cranking compression numbers since the a/f mix has begun to burn and expand.
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