I posted an issue to engine vibration last year, and I just now had a chance to figure it out. My cranking psi is 220 lbs on the low side and 230 lbs on the high side. I'm willing to bet on detonation. So I called Comp cams and they recommended retarding the cam 4*, since they grind them at +4*. I put that -4* figure in my Desktop Dyno and it actually showed an increase in power and torque. How much psi should I expect to loose? There guy said around 25 to 30 psi, which would put me back in pump gas range. Any suggestions??????