Compression Test Results, Too High?

[Greg Greer]

The previous owner of this car tracked it back in the day and had "hopped up" the engine. This engine was tired and had compression test ranges of: cylinder 1 =135 psi, cylinder 2 = 115 psi, cylinder 3 = 110 psi, and cylinder 4 = 60 psi (reason for rebuild, discovered broken rings). I replaced the old heads, pistons, and cylinders with the same part specifications that came off the old build. These parts were: 86 mm pistons and cylinders, cylinders were shimmed with .25 mm copper spacers, as before. The heads were also rebuilt the same, with Super 90 40 mm intake valves and stock 912 exhaust valves. The heads had been shaved in the past, but I did cut them anymore. I know the previous owner also installed a performance cam, however I do not know the specifications of that cam. After this top end rebuild, I have compression test readings of approximately 180 psi. Is this too high? Again, I replaced the old parts with new parts of the same specifications. What might be typical compression readings for such an engine? Thank you

[colingreene]

pretty difficult to know what it should be without knowing the intended ratio and the cam specs.

[mattC2993]

Way too high. You need to calculate the compression ratio based on head volume, dome volume, etc. Stock compression is around 140 psi. 180 psi is around 12:1. Run the test with the throttle plates open.

[colingreene]

Looking through old posts i found this and what sticks out to me is when tested my car makes 240psi for compression.