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FSM says Standard Value: 170 psi, Limit: 136 psi. Compression Ratio is 7:1. It says to check the compression on a hot engine (176-194 degrees) I checked it cold.


If your cam timing is off signifigantly your compression will be high, same goes for a worn cam or really loose valve adjusters.

Do you have mechanical lash adjusters that might be set loose?

Even having the wrong rocker arms can cause the same problem.

Also if yours is a truck motor the CR should be in the 8 to 1 range, not 7 to 1 unless you put in a set of turbo pistons.

I have gotten 180 PSI cranking pressure on a 7.8 to 1 2.6 engine and that had a turbo on it.

Are you sure the noise you are hearing is detonation? Did it get better with higher octane gas? How does the power on this motor feel? Does it pull clean to 5500 RPM?

Kevin C

87 Turbo Intercooled Raider, roller cam, torsen rear diff, LSD front diff, lockup auto with modified converter, V6 brakes, low transfer case gears...