Cam Duration

... I was talking to my friend and he is gettin some new cams and he mentioned the duration was 240. Well anyway, I never really thought about it until now, but how exactly do they measure that? I always thought it was how long the cam would leave the valve open, but that changes throughout the rpms, so i guess Im wrong lol. Insight plz? ...

The duration is the angle between the two lines which if drawn from the center of the base circle of the cam will intersect the two sides of the oval lobe. Life is the distance from the top of the base circle to the highest point on the cam. Lift Determines how much the valve opens, while duration is how long it opens for.

yea i realize it is how long it is open for, but how do they measure that? at 8000 rpm, the cam is spinning much faster than it is at 1000 rpm, meaning the valves are open for a shorter period of time at high rpms. If the amount of time a valve is open is a function of rpm, then what defines its duration?

Duration is specific to the geometry of the cam itself, but yes, a valve does open and close faster with higher RPM . For example if you have 2 cams, one with 220 duration and one with 240 duration, the cam with 240 duration will stay open longer at any GIVEN RPM than the 220 duration cam. Engine (A) has 220 cams engine (B) has 240 cams. Assuming same model engine with only diffrence being the cams, engine B's vales will stay open longer at any any rpm that Engine A. But of course if you take any engine with either cam , the higher the RPM is , the shorter amount of time its open for. Hope this answers your question!

no lol! i want to know how the duration is measured!!! for example, lobe height is in mm...

Oh, its an angle measured in degress.

If u have the cam in your hand you can measure it with a prescision protractor