Thread: Another, Cool things to know:Camshafts

Overlap

The amount of time, expressed in crankshaft degrees, that describes the window of time between the the Inlet Cam's opening point BTDC and the Exhaust Cam's closing point ATDC. This figure can vary between zero degrees on some stock cams to as much as 70 to 90 degrees on some race motors. In general most street engines will have 20 to 30 degrees of overlap and most performance cams will have 50 to 60 degrees of overlap. Increasing the degrees of overlap tends to move the powerband up the RPM band. Increasing the overlap can increase peak power, but only if the exhaust system is properly designed to scavenge the cylinder. Decreasing the overlap tends to boost lower rpm performance.

Lobe Centers

This is the angle between the inltake and exhaust camshaft lobe peaks described in camshaft degrees. Generally speaking the majority of cams will fall between 98 and 120 degrees. This angle dictates two important events: the valve overlap around TDC, and intake or exhaust valve closure delay there is in the relevant stroke (inlet/exhaust). Tightening the lobe center angle produces more overlap around TDC and wider angles mean less overlap.

Valve Lift

A little appreciated consideration is the effect of valve lift on engine performance. As the engine speed increases there will be a need to increase valve lift to keep the inlet speeds from exceeding the Mach Index value of .6, beyound which volumetric efficiency falls off. This leads to the possibility of planning your valve lift in advance relative to your design or performance goals be they street or racing.

shut ur mouth boy and speak engrish i just thought intake, exhaust, & tornado combo works and thats all you need for almighty power! whats a cam?

Another good write up from back in the day!