Valve Timing is critical in determining power output. With fixed profile camshafts, peak power can only be obtained for a limited speed range, which works well for an AC generator (constant frequency) application. This results in poor torque responses throughout the remainder of the speed range. The traditional solution has been a compromise which broadens the response curve but lowers the peak performance. With the advent of variable cam timing (Honda VTEC) it is now possible to broaden the response curve without sacrificing the peak performance.
The graph above shows the Horsepower responses of the CAM 125, as obtained from the dynamometer printout, and the O-320, as published by Lycoming. In order to obtain 150/160 Horsepower with the O-320 it is necessary to peak the power at the top end.
Variable cam timing allows the CAM 125 to outperform the O-320 at all speeds up to 2500 rpm.
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