Frank,
Consider this; why does any engine of a given displacement reach a point
where it begins making less horsepower at higher rpm? The same reason, say a
289 would make less horsepower at 6,500 rpm than at 5,000 rpm is the very
same reason a 376 ci engine makes less horsepower at the same rpm (5,000) as
the 289. The specific reasons include, for example, the manifold vacuum is
going to hell, which is indicative of volumetric efficiency, the result of
turbulent flow which increases friction, inertia in stopping and starting
the air mass, etc., etc. Even without valve float or any other extraneous
reason, as you increase an engine's rpm past a certain optimum, horsepower
starts to fall off. It's basically just a dynamic air flow problem; the same
induction, heads, cam, exhaust, etc. will peak at the same cfm regardless of
displacement or rpm.
Bob Palmer
rpalmer@ucsd.edu
rpalmerbob@adelphia.net
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