Thread: camshaft ??

Tweet

Originally Posted by sefrayser

Im looking at cams. Im under the old belief that the higher the lift the more lopey the idle. I know that is wrong. I have learned that a cam with a 114 LSA is more tame than a cam with a 110 LSA. Is this correct? Can someone please explain how to figure out which cams are choppy and which are tame?

You're on the right track. Lift has nothing to do with lope, it's all about lobe separation angle and the timing events of the intake and exhaust valves.
LSA is figured this way: If a cam is cut with an intake centerline of say....106 degrees ATDC and an exhaust centerline of say...114 degrees BTDC, you add the two together and divide by two....106 plus 114 is 220, divided by two is 110 lobe separation angle.
The smaller the lobe separation number, the snottier the idle, the lower the manifold vacuum and the motor wants to make power in the lower half of the rpm range more than it does up high. The bigger the lobe separation angle, the smoother the idle, the higher the manifold vacuum and the motor wants to make power in the upper half of the rpm range more than it does down low. Most hot rod cams will be ground on a 108-110 degree lobe separation angle and most hot factory cams will be ground on a 114-116 degree lobe separation angle....likely has something to do with manifold vacuum and power brakes.

Here's a degree wheel showing the timing events of a cam in advertised degrees....this is a 280/280 grind....This cam might be 220/220 to 230/230 @ 0.050", depending on ramp design.
http://www.imps4ever.info/tech/camsh...ing-schema.gif

This wheel shows the intake centerline at 102 ATDC and the exhaust centerline at 102 BTDC. Add the two together, get 204, divided by two, you get 102 lobe separation angle.
http://www.alfabb.com/bb/forums/atta...1&d=1189535925

.