440 Compresion Test

[1968 Valiant]

What PSI is healthy for 78 440 RV motor..?
I know what the compression ratio is. I am looking for what reading I should have with a simple compresion test. It has 452 Heads

 

[Rob Eppler]

Healthy, meaning in good shape I presume! Stock cam, good battery for proper engine cranking rpm, I say 150 to 170 would be very good. If it still has the stock pistons, 125 to 150. would still be very good.

 

[Jim Lusk]

The cam makes all the difference. What you want to see is similar numbers in all cylinders. Definitely fully charged battery, all spark plugs out, and throttle wide open.

 

[HemiEd]

The cam makes all the difference. What you want to see is similar numbers in all cylinders. Definitely fully charged battery, all spark plugs out, and throttle wide open.

Jim, that is great advice. I have been doing these compression tests forever, and never thought about having the throttle wide open.

 

[Murray]

Compression tests are only important to determine the eveness of the cylinders. The actual amount of compression is relatively unimportant in a street car. You should be looking for all cylinders to be within 25-35lbs of each other. If one cylinder is 75lbs and the others are 150lbs, then you have a problem. I remember a compression test on a '64 Galaxie 427 side-oiler, compression was 100lbs all cylinders. It ran smooth, good. No problem, the motor was just tired, worn rings, but evenly worn.

 

[Purple Haze]

Jim, that is great advice. I have been doing these compression tests forever, and never thought about having the throttle wide open.

Yeah, make sure the engine is hot too.