Lobe separation

[wantmorepower]

Can anyone give me a basic description of the effects that different lobe separations have on cams. Say I had two cams that were identical as far as intake/exhuast durations and lift. How would those same two cams perform with different lobe seperations?

I was looking through my summit catalog trying to decide on the cam i will buy and thought i had it all figured out untill i noticed that some cams had different lobe separations than others.

BTW this is not a f-body specific question. I realize that the cam selection for our cars is still limited at this time. I am trying to find the perfect cam for my 318.

[Dominic]

Lobe separation is just what it says, it determines the amount of valve overlap (the time when both intake and exhaust valves are open at the same time). Usually going to a lower lobe separation means you need to go with less duration to get the same driveability; alternatively you can increase the lobe separation (spread them out a little) and run longer durations to get more upper end without sacrificing the idle quality as much. A 318 is going to need a cam roughly like our 3.8L V6s due to the similar piston stroke/bore (ours as a V8 would be like a 5.0L :D )

There is no correct lobe separation, you can run more duration and less LS and get almost identical power as less duration and more LS. Usually a general rule is anything 112 and below LS is going to chop at idle, 110 makes it lope across all cyls and almost stall if you don't increase the idle RPM to 1000-1200. 113-115 idles well and usually causes no problem at stock 650-800RPM idle speeds, with the higher LS idling smoother and more stock.

I read an article the other day where the EPA discovered that cars with more valve overlap actually produced less NOx emissions than those with more overlap, since it worked similarly to having an EGR by blowing a little exhaust into the intake in between strokes [img]smile.gif[/img] . The cool part about it was unlike EGR it didn't increase the HC emissions... EGR increases HC emissions while NOx goes down (bad trade off if you ask me).

[ December 05, 2002: Message edited by: Dominic ]</p>

[wantmorepower]

Thanks dominic. Your explanation has made it crystal clear.

[wantmorepower]

I think that i have found the cam for me. Have you had any positive or negative experience with the line of cams that summit offers as thier own cam. (They sell most brans but they do have cams that they throw their names on and usually sell at a discount when compared to name brand manufacturers)