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Old 08-17-2009, 10:39 PM   #8
NoDOHC
The quest for more torque
 
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Location: Sheboygan, Wisconsin
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If you take both leading plugs out and can get a friend to hold the gas down and crank the car. As long as you have a 550 CCA + Battery, you should get about 375 engine rpm driven on the starter. With the valve removed from the bottom of the compression gauge, watch how high the gauge bounces when cranking. It should bounce to 80-120 psi (110 is good for turbo, 120 is good for NA). With 5,000 miles on a rather meticulous rebuild my turbo engine made 120 psi on all faces, front and rear.

You want to make sure that the gauge bounces rather quickly (goes up, down, up down) any pauses in the needle at zero indicate a bad face. A long pause could indicate two bad faces (bad or stuck apex seal) while a short pause indicates a single bad face (bad or stuck side seal).

I hope this helps you a little.

Two notes:
Never check compression after flooding the engine - it will always read low (60 psi or less).
If the engine starts every time, idles well and has good low-end torque, your compression is probably acceptable.

Another interesting note on compression:
If you have good compression, you can flood the engine (like putting a 3 bar tune in the ECU while using a 1 bar sensor) and after you get the appropriate tune in the ECU the engine will start fine without going through a deflooding procedure. (Needing to deflood all the time is usually a sign of bad compression.)
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1986 GXL ('87 4-port NA - Haltech E8, LS2 Coils. Defined Autoworks Headers, Dual 2.5" Exhaust (Dual Superflow, dBX mufflers)
1991 Coupe (KYB AGX Shocks, Eibach lowering springs, RB exhaust, Stock and Automatic)
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