A, B or "touring" cam?

[Jim Brierley]

Originally Posted by Gene F

I get it that lift means the valve travels higher, and gets more breathing. But what is the duration (in plain english)?

Seat-to-seat duration is about 254 crankshaft degrees on a stock B cam, 260* on the .339" lift cam. Duration on a 260* performance cam will out perform the same duration on a stock cam because the rate of lift is greater. The .050" figure is a random figure used by many grinders because the rate of lift may vary as done by different grinders, .050" tends to give a better idea of how the cam will run under racing conditions. Too much cam in a stock or near stock engine can actually hurt low-end power, so stay on the mild side for street (touring) use.