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Originally Posted by speedshopmike
has anyone ran a compression check on their fresh, stock 455HO?
if so, what's your average psi reading?
i'm trying to get a handle on the car i bought; it's making only 110psi.
no smoke, no bad noises, no blow-by, no gassy smell in the oil, and documents indicating a rebuild less then 10k miles ago - ie, my judgement says the motor's still internally happy.
it has an unknown aftermarket cam; i'm looking to see how much of my low result is in the 8:1 compression and how much may be related to a too-large or improperly set up cam.
given the round of badly marked timing sets that abounded for a while, i'm thinking there's a fundamental cam timing issue (it feels and acts retarded) crippling this HO.
former owner installed it dot to dot per usual practice, but if the dots are in the wrong place...
quick and accurate replies are appreciated.
thanks,
mike
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Mike - 110 PSI all the way? If so I'd say that your rings and valve sealing is good, but the camshaft is WAY too much for a stocker engine.
A "tight" 068 cammed 455HO ought to make at least 140-150 PSI cranking.
Unfortunately my GTO engine is tired, and has an 041 cam in it, so not a good comparison. My Formula engine is a 10:1 deal with a SMALL solid flat tappet cam, and it averages 215 PSI cranking!
Did you block the throttle open when testing? Are the battery and starter in good shape and giving you a brisk cranking speed? All things to consider when running a cranking compression test.
110 PSI cranking compression would be a gutless PIG.