Thread: Engine Upgrade

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"Advertised lift".....You're gonna start confusing yourself. There is no such thing as advertised LIFT. There is only LIFT at the cam and LIFT at the valve. LIFT at the cam is a direct reading measurement of the difference between the base circle of the cam lobe and the highest eccentric point of the lobe. LIFT at the valve is a the actual movement of the valve from its seat (with the tappet on the lobe on its base circle) to fully open position (with the tappet on the lobe at its highest eccentric point of the lobe). Lift at the valve includes a theoretical rocker arm ratio which magnifies the cam's work. In other words, if the tappet lift at the cam is 0.300", then the valve lift with a 1.5:1 rocker ratio would be (0.300" X 1.5) or 0.450" at the valve.

There is advertised DURATION and there is DURATION @ 0.050" lift.

"The 223 lift @.050 cam could have an advertised lift as high as 280?"

Yes, it could. The smallest difference that I have encountered was with a roller cam with 37 degrees difference between advertised and 0.050" duration. The more difference there is between advertised and 0.050", the lazier the design, but the easier it is on the valvetrain. Back in the 50's, I remember some Chevy cams that had 70 degrees difference. In other words, 300 degrees advertised and 230 degrees @ 0.050". (Which would have meant 35 degrees on the opening ramp and 35 degrees on the closing ramp between about 0.006" and 0.050" tappet lift. Very smooth and easy on everything)


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