Compression Test???

I will be doing a compression test on my 79 /I6 and would like to know the acceptable range per cylinder?

 

my 81 manual shows 120lbs-150lbs acceptable with 30lbs being max varitation between cylinders
should be close for the 1979 model as well

 

Thanks Jim.

 

Jim, after your helpful answer I researched it a bit more and also came up with 150psi specifications with 135psi-165psi being in the normal range. Thanks.

 

I read somewhere that there was some kind of conversion where you put in a thicker head gasket and lowered the pressure to around the 110 - 120 mark. I dont recall why but I do remember reading this. mine was 125 average with 10 +- on all cylinders

 

You can calculate what the head gasket thickness is from the compression ratio, combustion chamber volume, bore, stroke, and deck clearance. Use the relationship P1*V1 = P2*V2, and include the atmospheric pressure. I'd be happy to do if for you, but it's a quadratic in gasket thickness and I don't have time to follow through right now.

258 combustion chamber volume: wedge head 64cc, quench head 68.5cc
258 deck clearance: 0.110" wedge head, 0.069" quench head.
258 bore, stroke: 3.75", 3.895"

The spec for my engine is 150psi, max variation 20psi between cylinders, and I measured 160/160/160/150/155/152psi. This is within spec (on the high side - lucky me!)