BillJack

I have a '64 Olds 394 Starfire engine, 345 hp. What lbs/square inch (PSI) should I see when I do a compression test? Results taken last evening are as follows: cylinder 1-180 psi, 3-185, 5-182, 7-168, 2-180,4-161, 6-189, 8-166. Thanks for you help!!

Don R.

When I got my 63 six years ago the engine was said to be rebuilt with about 3000 miles on it. I did a dry compression test and got 180 to 182 psi all around which I was very happy with. Your numbers look good to me.

BillJack

Thanks Don for taking the time to relay that info to me! Much appreciated. I suppose then that my engine is in decent shape. I still need to do a carb rebuild and repair the exhaust leak. Thanks again!

BillJack

I looked in an old "Motors Manual 1966" that I have. It says the 394 compression is 190 psi. So I'm a little low on seven of the eight cylinders. I did not test with ALL plugs removed. I tested with only one plug removed at a time. I will retest to determine if this will make a difference.

Don R.

That will make a difference, don't know which way. My test was with all plugs out and carb wide open, but the engine was cold, ideally it should be hot.

OLDSter Ralph

You're probably good enough. There might be a range that's acceptable like 170 to 190. This is a dry test ?

B964

Should be an acceptable PSI range and a percentage difference value. If acceptable was say between 160 to 180 you still wouldn't want seven at 178 and one at 161.

Ozzie

The 1964 Oldsmobile Service Manual (number 1) page 5-3 says to open choke & throttle, remove all spark plugs, and be sure battery is charged. The lowest cylinder should not be less than 80% of the highest, and no cylinder should be less than 100 PSI. A bit of oil can be added to the cylinder to check for ring problems.

OLDSter Ralph

BillJack, you can't get any better than from Oldsmobile. I was using 10% variance off the top of my head. Recheck compression PSI and let us know.