Reply to "Questions regarding George's 275/285 Custom Street Cam Profile"

Carl, since there is 6° difference between intake duration and exhaust duration the cam you describe reminds me of a cam designed using one of the laptop dyno programs.

The first thing I noticed is the cam has fast ramp lobes (52° lobe intensity) yet only 0.520"/0.531" lift. Seems as though whoever put this cam together placed emphasis on duration at 0.050". The 351C 4V heads are going to make peak BHP at 6000 rpm even if the duration at 0.050" is only 205°! That's the intake duration of the Cobra Jet cam. The 351C 4V power band is not as dependent on duration as it is with other engines, but to make power the valves need to be opened as high as possible (within the limitations of engine longevity) to take advantage of the cylinder head air flow potential. Lobes are available today allowing valve lift in the 0.550" range (or more) with reliability.

The valve event timing is just fine, the overlap is low (57°), it is more or less centered within the window it should be centered within, that window is the piston's "dwell" time at TDC. However due to the 52° lobe intensity, overlap at 0.050" is 5°. I'd like that better if it were closer to zero. The exhaust valves are opening and the intake valves are closing where they should be based on advertised duration. But I'd prefer it if the intake closing at 0.050 was 40° or 41° ATDC instead of 45° ATDC. Those are the various boundaries I try to stay within to insure good low rpm performance.

The cam should work fine, but if lobe intensity were 57° instead of 52° (225°/231° duration at 0.050) that would correct both the issues I cited. The lobes are symmetric, if they were asymmetric that too would correct the issue I have with the intake valve 0.050" closing event. Power would improve if the valves were lifted higher.

I haven't purchased wheels yet, I'm working behind the scenes with someone on a project related to that subject. I won't make a wheel purchasing decision until I know if the project is go or no-go.