What is the formula for calculating the amount of valve overlap?

Just add the numbers on the cam card from where the intake valve opens to where the exhaust valve closes.

DAVE

Best way to calculate overlap is to add the Intake Open point to the Exhaust Close point. For example, my cam card lists IO=20*BTDC at 0.006" and EC=18*ATDC at 0.006". So, overlap at 0.006" is 38 crank degrees.

If you want to know it at 0.050", your card may not list IO and EC at those points. But the card should give you intake duration and exhaust duration at 0.050". Add 1/2 of the intake duration to 1/2 of the exhaust duration, then divide by 2 to get it in cam degrees. Subtract the Lobe Sep Angle (which is in cam degrees) from that number to get overalp at 0.050". So, for my (weak) cam, 212/2=106 + 218/2=109 == 215/2 =107.5 cam degrees of duration. 107.5-112(LSA) = -4.5 (my cam doesn't overlap at 0.05").

Hope that's what you were looking for.

Thanks, that is what I thought. But when you run the numbers at zero valve lift, the numbers seem real high.