Cylinder compression???

[ohiowhitetail]

I have to start working on my '99 350 7.3L tonight. I've got blowby in a cylinder, so she's parked until I get her rebuilt. After looking for days, I still can't find any specs about what compression I should expect on a properly-functioning cylinder. Can anyone help? I need to run a compression test first thing.

[djsdiesel]

370-400 psi, on a good engine. As low as 350 will still run.

[ohiowhitetail]

Thanks, I've heard all kinds of numbers, but yours seem to be the most reasonable. I couldn't imagine an engine carrying 500 psi like a couple folks suggested somewhere else.

[djsdiesel]

No way will thay have 500 psi. I think 420 is the highest i've seen and thats becaus it had a little oil in the cylinder

[kaptainkimball]

as far as compression ratios, i have heard rumors as far as 19:1 after being turboed, but dont quote me, i am not possitve. i have never read anything to know for sure

[lanny251]

350 is bare minumum!!!!
320 is to low to combust the fuel....
I had a truck in my shop about a month ago that averaged 550psi except for one that was 350.
Make sure and use a reputable compression tester that at least goes to
1000PSI if you use one that goes to 500PSI and you have a cylinder that goes to 550PSI you could have problems(trip to ER)

[sldghamr]

i used to have an '89 Ford Diesel years ago. per the Chilton manual that i had, the compression was about 21.5 to 1. i now have a '96 and the compression is about 17.5 to 1. don't know if that helps................