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Normal acceptable compression numbers '86 270 hp

P

Pretty Work

New member
Gents,

I am new today. Have searched this question but haven't seen a clear answer. Would like to know what acceptable range is and also, what is the procedure, ie, warm engine, cold engine, throttle position on a carbed engine?
 
You can do both a cold and warm test.
Remove all spark plugs, disconnect the power supply to your ignition system (this will prevent coil damage), and open the throttle plates.

Cylinder pressure readings are not accumulative, other than equalizing the gauge and hose.
You'll want to cycle the engine through a minimum of three compression strokes.
Depending on which stroke you begin with, this may mean six or seven crankshaft revolutions!

Many will suggest that your lowest cylinder pressure reading should be no greater than 10% difference from that of your highest reading.

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RicardoMarine said:
You can do both a cold and warm test.
Remove all spark plugs, disconnect the power supply to your ignition system (this will prevent coil damage), and open the throttle plates.

Cylinder pressure readings are not accumulative, other than equalizing the gauge and hose.
You'll want to cycle the engine through a minimum of three compression strokes.
Depending on which stroke you begin with, this may mean six or seven crankshaft revolutions!

Many will suggest that your lowest cylinder pressure reading should be no greater than 10% difference from that of your highest reading.

.
Click to expand...
Thanks, Rick. What PSi's should I look for? 140's? 180's ? Thanks again.
 
What pressures to expect will depend on the engine build!

Piston profile, cylinder head chamber volume and camshaft duration, all play a role in static cylinder pressures.

If I had to take a stab, and with a guess that this engine has the GM full dished pistons, I would say that you should hope for pressures around 165 psi or so.

If you know the build, go to Sick's Engine Compression Ratio calculator (interactive on line version), and plug in your numbers.


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Pretty Work said:
Thanks, Rick. What PSi's should I look for? 140's? 180's ? Thanks again.
Click to expand...

Ayuh,..... Generally speakin', for all of our motors, All cylinders at 150 psi(+ or - 15%) or above, is a Healthy motor,...

100 psi or below is a Problem,...
 
GM formally redefined their standard production product compression test procedure a while ago...summary follows: cold engine, throttle wide open, ignition coil output to ground, all plugs out, 4 compression strokes per cylinder.

minimum compression => 100 PSI

Variation = min compression => 70% of MAX compression
 
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