quote:
Originally posted by greg's 66:
... is there a better lobe that can open the valve more at the right time? And stay within street parameters ...
Better in what way? More lift?
Based on my calculated figures for duration at 0.006 and my recommended mathematic intake centerline of 109° ATDC, the seated valve events for the Crane cam are thus:
EVO = 77° BBDC
IVO = 29° BTDC
Overlap = 56°
EVC = 27° ATDC
IVC = 67° ABDC
Overlap of 56° is great, and overlap occurs within the dwell period; great stuff. The exhaust valve opening at 77° BBDC seems a little late, but remember its based upon my "guess" of what the duration at 0.006 is ... it may open a bit sooner. However, in combination with the exhaust system you've described, I'm sure the engine will rev to 6500 rpm or more. This cam is "good enough", if peak BHP at 5500 rpm is good enough for you.
quote:
Originally posted by greg's 66:
... How much power gain is a good port job worth on a set of heads and intake like mine ...
I don't have experience with those heads, and I'm not sure which intake manifold the engine is equipped with. I'm guessing its the manifold that looks like the Edelbrock Air Gap manifold, i.e. a dual plane manifold?
Before I could comment I would need to see what the "transistion" from valve pocket to combustion chamber looks like. As is true for any cylinder head, you want a nice, smooth, well blended transition from the valve pocket to the throat, a "rounded" throat, a nice, smooth, well blended transition from the throat to the valve seat, and from the valve seat into the combustion chamber. Done right such work is worth at least 20 BHP with the iron 4V heads.
I would also like to measure the size of the "throat", i.e. the minimum cross sectional area just above the valve seat. The “throat” should have a cross-sectional area of about 2.3 square inches (i.e. 1.70 inches diameter) thus preventing limiting port velocity (sonic choke) from impacting the engine within its power band.
