Could anyone tell me what factory acceptable compression specs on a 4.5 should be? This engine may be replacing my 4.5 Euro series in my 1979 450 SLC. It has 145 +/- 3 psi in all cylinders, and was rebuilt 40,000miles ago. There should be papers showing all maintenance that was performed before the car was totaled.

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10702312013187

145 sounds fine. Typical compression on gas engines is 125 to 150 psi. You also want an even spread within 25 psi, such as yours. I never saw a compression gage that was really accurate to 3 psi! Also remove the spark plags and look at them. Excessive carbon or oil would be a warning flag. A good visual of the exterior for oil leaks etc should also confirm the reported o/h 40,000 miles ago.

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Deezel
87 300TDT
150,000 miles