Compression numbers

[sleepyvr4]

Well, thought I was golden on a 6bolt 4 bolt dsm swap candidate for cheap.

Supposedly rebuilt longblock with 3A valvejob, ARPs and new pistons - 5k on new motor. Runs/pulls hard. however compression told a funny story.

I was not there. My guy mentioned 110 110 110 150 psi - spoke to owner and 110 125 135 150 across board.

They ran a few checks. Looks sketchy. The car may be a good deal if a rebuild works out.

So far we got ideas of sh*t valve job, pushing head gasket, crap bottom end, warped head, etc...


I wanna low ball. I dunno. ideas appreciated...

Thanks

 

[Wizardawd]

Do a wet test and it'll narrow it down. If the numbers skyrocket, worn rings. Anything under 140psi on 7.8:1 pistons is weak with normal being 150-160psi. Also, 14psi variance between cylinders is the max.

And after the wet test, do a leakdown test. Using the compression tester hose, pump the cylinder full of air with that cylinder at TDC. Listen for where the air comes from. Air filter, intake valves aren't seating, exhaust...obvious, radiator cap (look for bubbles)is a headgasket leak, oil cap/dipstick is blowby past rings. There will always be a little leaking, but look/listen for the big leaks.

PS: Make sure the throttle plate is open when doing the test otherwise your numbers will be off.

Wiz