Chevrolet Repair: Engine Compresion, max compression, swept volume

Question
I have a 1991 corvette w/ TPI and have recently had the motor rebuilt. The car seems to be a little sluggish to me so I checked the compression. I turn the car over about 4 times the first 2 revolutions the compression jumps to 120psi on the 4th revolution the compression is 180psi were I think it should be for a new motor. Is this common for all cylinders to not just go to the max compression first. Could the cam be off a tooth?


Answer
That is completely normal.  An engine will not create spec compression on first or second stroke.  Swept volume is not efficient when cranking.  Try and remember the engine revolves at 600-900 RPM at an idle when piston velocity overcomes compression leakage through rings etc.  If the  engine seems sluggish make sure to check fuel pressure and most importantly ignition timing.

Wayne