A camshaft's intake closing point has more effect on engine performance than any of the other three opening and closing points. The earlier it occurs, the greater the low-rpm cranking pressure. Early intake closing is critical for low-end torque, responsiveness, and for generating a broad power curve. It also reduces exhaust emissions while raising fuel economy.

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As rpm increases, intake charge momentum also increases. This results in the intake charge continuing to flow into the combustion chamber against the rising piston far past bottom dead center (BDC). The higher the engine's operating rpm, the later the intake closing should be to ensure all the charge possible makes it into the combustion chamber. But closing the valve too late creates significant reversion. It's a fine balancing act.

In a perfect world, the optimum intake closing point would occur just as the air stops flowing into the chamber; would get the valve seated quickly and not waste time in low lift regions where airflow is minimal and there is no compression building in the cylinder; wouldn't be so fast the valve bounces as it closes, allowing the charge to escape back into the intake port and disturb the next charge; and, with a hydraulic-lifter street cam, would ensure the closing ramps aren't so fast they result in noisy operation.

Contact

Comp Cams; Memphis, TN; 800.999.0853 or 901.795.2400; CompCams.com