The 1970 '383', had a better Camshaft and higher 'Load-Rate' Valve Springs than than the 1966 and 1967 '383'.
The 1966-1967 {383/325 HP} was a poor runner, so much so, that the NHRA 're-factored' them down to 280 Horsepower, just so they could be somewhat competitive in later years.
Plus, the 1968 and later 383's had better Exhaust Manifolds.
The Intake Manifold also had greater runner sizes, and bigger ports, as well as the Carter AVS {625 CFM}, which was
a much better Carburetor than the Carter AFB {575 CFM}.
YY-Man,
I saw those 1966 and 1967 383/325 HP cars run back in the day, and they were 'painful to watch' going down the Track.
