How are these compression #'s


New Member
Jun 14, 2004
Need some words of wisdom from those in the know. My 87 T has 135,000 miles on it, runs great no complaints there. Pretty much stock engine has never been opened but has many updates and the usual mods done to it. Anyway it leaks oil like a siv, needs the rear main seal replaced, the oil pan gasket replaced and valve cover gaskets. I have been putting replacing those off with the thought of a rebuild sometime soon. Not sure that day will ever come so I did a compression test, the #'s are this 155, 152, 150,145, 142, 140. Does anyone know what the spec says the compression "should be", and are these good numbers, is it worth just replacing my leaky gaskets and pressing on or should I wait and rebuild. Thanks in advance for the advice. Jeff
There are really not set #'s for compression test. Those numbers look real good though. Anything over 135-140 is good. Once you see below 100 you might start having misfire issues. I believe GM goes with "If the lowes compression is more than 10% of the higheist comrpession #, then you have compression issues" Hope this helps!
for the miles that you have on your car those #'s are good. As far as is you should do the gasket. yes you should oil pan is no big deal. rear main is a PITA but take your time and do it right and you will be happy. valve covers are easy as well. your motor should last a long time. fix the leaks and keep beating on her.