Okay, so I'm looking at two possible cams for my upcoming setup (that may be coming quicker than I had planned due to a possible blown head gasket).

Stock LB9 bottom end. Ported/gasket-matched LT1 heads (hopefully flowing around 250/170) and intake, 24# injectors, 1 5/8" headers, full 3" exhaust, MAF induction (possibly SD in future). CR will be between 9.5 and 10.2.

I'm considering the ZZ4 cam with 208*/221* @.050" and .474"/.510" lift on a 112LSA.

The other is an Isky rr-257/265 cam with 209*/217* @ .050" and .465"/.485" lifts also on a 112LSA. Adv. duration is 257*/265*

Its a daily driver that will see track time. Gears and stall will be matched to whatever the car needs after this work is done.

Nitrous is a possibility in the future and I figured the ZZ4 cam would be great for that because of the larger split-pattern profile, but this is NOT something I am really basing my decision on.

I don't want the idle to sound too un-stock, and I still have to pass emissions.

As for comparing cams in DD2k... I've noticed that the "valve overlap" changes when you go from seat-to-seat specs and .050" specs. Why do some cams have such different valve overlaps, and I'm assuming I want as little overlap as possible. How does DD2k show that some cams have negative overlap?? Also, does anyone know what the "advertised duration" is of the ZZ4 cam? Are the ZZ3/ZZ4 cams the same?

 

Am I better off with the Isky 209*/217* .465"/.485" or the ZZ4 208*/221* .474"/.510" for a daily driver? The Isky is slightly cheaper and comes with new lifters as well (neither are being bought at retail price).

 

They're going to be a pretty close call, probably. Plug them both in and see what happens. Remember to check out their curves both N/A and on nitrous.

Using the .050 duration numbers will probably give you a more accurate estimation of the actual power curve, but there are still many cam specs that DD2000 just kinda "fudges" and assumes is the same for all cams (which, of course, it's not).

Overlap is simply a measure of how many degrees the intake and exhaust valves are BOTH open as the piston passes TDC between the exhaust and intake stroke. Advertised durations will always be bigger numbers than .050 durations, obviously, so your overlap will appear larger when using Advertised duration numbers.

Overlap is not necessarily a "bad" thing or a "good" thing. Depends on the application. It's just a function of how cams work and overlap is a natural by-product of that. More overlap will happen any time you increase the cam's duration or decrease it's Lobe Separation Angle. Both of these traits are usually associated with higher performance cams, and that's why really "aggressive" or "lumpy" cams usually have lots of overlap.

Your prospective cams will have around 0* or less overlap (measured at .050 duration). Might be slightly negative (-8*) but somewhere around there. That will generally translate into a relatively smooth idle. Higher overlaps generally mean worse idle quality. Higher overlaps are also more difficult for a factory fuel injection system to run the engine correctly. Too much overlap and drivability can get pretty miserable. Your prospective cams will have no such problems.

 

You get two different overlap specs because you're putting in two different reference points to measure from.

When using .050" the program measures from .050" before the exhaust valve is closed to .050" after the intake valve starts to open.

When using the advertised duration DD2000 assumes it's taken from .006". The difference in rotational degrees from a cam opening .006" and a cam opening .050" is a lot.



Is the Isky cam a hyd. roller? Is that what the "rr" means at the beginning of the part #?

The split is the same. But because of the small increase in the ZZ4 cam's exhaust duration, there will be more overlap. So, as far as that goes, the Isky cam would be the one based on you not wanting much overlap.

If the Isky isn't a hyd roller, the overlap based on advertised duration will be completely different because of the lazy opening of hyd cam over a hyd. roller.

Sorry, but I can't find the ZZ4 cam specs other than what you have.

 

Ah yes both are hydraulic roller. I'm probably going to end up going with the Isky if the guy gets back to me. The lift isn't as high, but the exhaust lift on my heads isn't as big of a difference as the intake lift anyways, and the intake lifts on the two cams are somewhat similar.

I plan on buying 1.6rr's in the end anyways.