I finally learned about cams and what all those lift and duration numbers stand for. Heck id like to before i get one. But what is overlap. I have yet to understand this concept. I hear in mags such as the last GMHTP when they were getting the extra 20hp out of the engine, that overlap was ok. So again, what is it? and is it good or what?!

 

I finally learned about cams and what all those lift and duration numbers stand for. Heck id like to before i get one. But what is overlap. I have yet to understand this concept. I hear in mags such as the last GMHTP when they were getting the extra 20hp out of the engine, that overlap was ok. So again, what is it? and is it good or what?!

 

Basically overlap is the amount of degrees that the intake and exhaust valves are open at the same time. When the exh and intake are both open, some unburnt fuel will be sucked out the exhuast. This kills your mileage, makes your emissions go up, and give you that killer lopey idle <img src="images/icons/grin.gif" border="0"> It also decreases low-rpm torque, and hurts throttle response. Increasing duration gives you more overlap, but makes more power up high.

J.

 

Other than the lopey idle which many say sounds awesome, Overlap is bad than? A friend of mine, not sure which series, i think (dont hold me to this)has a Comp 222/222 .563/.563 112LSA. he says it has and awesome lope but does this have overlap and does anyone here have it?

[ December 02, 2001: Message edited by: R U A LS1 ]</p>

 

Overlap is good and bad, if you want to pass emissions testing it is bad. It also hurts your fuel mileage to some extent. Typically a cam with more overlap will make more power though, because the factors that cause overlap also contribute to power.

Your friend's cam has more overlap than stock. Any performance cam is going to have more overlap. This leads to less effiecent operation at idle-low rpms (which is why mileage falls off and such) but makes the engine more effiecent at filling the cylinders at higher rpms.

J.