340 street build help from experienced input
Single pattern cams allow as good as no timing adjustability, and unless it is installed straight up, any timing change subtracts Effective overlap.
Ok that is worded wrong I think; You can time the cam anywhere you want to lol. But here's the deal;
If this theoretical single-pattern cam had a mathematical overlap of say 46* at split overlap AKA straight up. And say you advance it the typical 4*. By doing that you loose double that in Effective overlap, which cannot be more than double the smallest half of the overlap, so in this case 2 x 19=38*Effective .
IMO, loosing this much overlap is bad for this combo. If OP had log-manifolds, the overlap has no meaning and you could almost ignore it entirely.
Take that same cam with 46* overlap, but with an 8* split, and install it 2* advanced, the Effective overlap becomes the same as the mathematical overlap. The penalty for this phenomenon, when keeping the LSA the same, is 4* less intake duration, and 4* more exhaust duration. But
keeping the same intake duration and same Effective overlap, the LSA changes just 1 degree and the exhaust grows 4 degrees. with 4* split, whoot-whoot. So now this cam can be moved in either direction and still loses double thee change, but it is already 1*advanced which is also 1* advanced from the single pattern, but the single pattern, for the same intake duration, had only 38Effective overlap compared to 46 with the 4* split. For this combo, IMO, we have to play this cam business pretty tight.
How I get my numbers is;
I play the numbers off the Ica, and put a reasonably sized amount of overlap on the cam, then calculate the other numbers from those, being ever mindful NOT to drive the LSA to tight. And I try to work with known camlobe sizes to make it easier on the cataloging, Cuz you know, if I come up with what I think is the perfect cam, but nobody ever heard of the lobes, what good does that do anybody.......