Apparently my old evo with 90,000 miles had 190 , 170 , 170 , 190 compression.

What is considered bad compression?

Is 145 normal?

Thanks

John

 

Matter where you live im in denver and good compression is 120

 

145 is ok was that with the engine warm or cold? also with aftermarket cams or without?

 

The overall number is certainly important to a point, but the variance between cylinders is, IMO, more important. I think you want them each within 5% - 190-170-170-190 indicates something isn't quite right. In other words, I'd rather have 145 across the board than a significant jump from one cylinder to the next. Two things - make sure the car is warm and that the TB is open. You can hold it open with your foot or with a clamp. Make sure the battery is strong as well.

 

i think 5% is a little on the strict side. im not sure on these motors though. i know with most the cars i see at my shop which are just DD's your normal cars i usually go by 20-25% difference depending on the motor.

 

do the test again with the battery on the charger, about 12 cranks a cylinder or however many it takes until the needle stops moving.

as others said with the gas pedal pushed in.. in my opinion a leak down test is far superior then a compression test.

20psi variance though is not a good sign. its possible the headgasket is compromised.

 

generally with the leak down you can hear where the excessive leaking is coming from as well.

 

It depends......

If you have a high buck drag car you'd want the compression to be perfect - the maximum across all cylinders, If your car is a DD with 250K but is still running okay, just be glad it has compression.