Hey guys, still hunting for the engine to power my project. Im being real picky on the engine and have pasted or turned down a few. But i just had an idea and ordered a comression adapter from Snap On, not worried about the Head gasket or valve job as that will get replaced and reworked anyways but would like to start with a tight short block. question is what should the static cranking pressure be on a 94-98 12v cummins? When i find my engine ill start by checking all 6 holes with the comp. tester. Then pull the head and have the valves vac. tested and i should know the condition of the rings, my thinking anyway. My gas motor comp. gauges go to 300 i fiqure the ol cummins to be prob. even north of 400 am i right????? Thanks guys

 

The compression pressure will depend on cranking speed. Expect to see above 300psi, my 270,000 mile engine runs in the 380psi range with all cylinders within 10 psi at cranking speed.

The difference between cylinders is really what you want to look at, I don't remember the spec, but the closer the better.

 

Thanks, ya around 2% they say from each other. You said yours is within 100psi of each other? isnt that more like 25+%.. Just want to confurm short block tightness before i put 60+ boost on her. Ive heard the cummins rings are stainless steel anyone know if thats true, heard of cast, chrome, moly, plasma,etc.... but not S.S. , sounds good though prob. would handle heat well.

 

Oops, I meant 10psi, I changed it my original post.

 

Anyone else know what a tight short block should pump up to assuming a fresh battery and good starter? Thanks

 

380psi and up would be my guess. My old 89 with 250,000 miles had compression of 380 psi before I put new injectors in it..

 

Thanks, 380 psi it is.