Can someone explane to me what the duration, lift, and all that stuff about cams. Like what they mean and how they affect your engine.
Zak - Below is a link to Crane Cams FAQ page on cams & valve trains. It's just the basics, but should give you a better idea. Crane Cams
Ok, so what in a cam gives you a rough or choppy idle? And is the lift what makes a cam big. Can someone give me specs for a cam that has a choppy idle and one of a big cam? Or are they the same. thx
Overlap. In a BBB, anything over ~13-15 deg overlap ( @ 0.050" tappet lift) can give you a rough idle. 20 deg overlap or larger will give you a choppy idle. Big overlap is gotten by close (narrow) lobe separation angles (LSA, or lobe centers, LC), or lots of duration, or both. No, but it makes for a high lift cam. But when someone says "I've got a big cam", they usually mean duration, because that's the parameter than will mainly govern the engine's characterisitc properties. How big is big: Street car big or Top Fuel big? Anything equal to or larger than TA's 238 deg @ 0.050" intake/ 248 deg @ 0.050" exhaust on 112 deg LSA will give you a rough-to-choppy idle. It has 19 deg of overlap: [(238+248)/2 - 2*112] .
I don't think getting a cam with a choppy idle just for the sake of having a choppy idle or being able to say "I've got a big cam" is the best strategy. You can achieve lots of goals with a cam that doesn't have a choppy idle.
