Originally Posted by Az_bronco_rob

I think there is some confusion of terms. Compression ratio is determined mathmatically, a compression test is done in the real world, and can be done on a motor lying on the ground, so long as it has the heads on it and a starter bolted to it. Just open the carb or TB to wide open, screw in a compression guage, and take a battery (freshly charged) and jump the starter motor to make the engine turn over 5 or 6 revolutions (make sure you strap the thing down!). You should get a minimum of 90 psi. More important is that the value be consistant among all the cylinders - if it varies more than 15% then there is a problem with the motor. Keep in mind too that if you squirt some oil in the cylinder it will read much higher, especially if there is a problem with the rings and/or cylinder scoring.

Originally Posted by Az_bronco_rob

You should get a minimum of 90 psi.

Originally Posted by mjr46

actually 100 psi is the standard that most accept as needed for complete cumbustion

Originally Posted by alansupra94

Thank you for jacking my thread.

And I not talking about compression RATIO, I am talking about compression NUMBERS like when you check a motor in every cylinder and measure the peak pressure after cranking a number of times.

I guess no one knows then. I will assume less than 10% difference between cylinders is good enough to know if the motor is good.