Mopars 1968 '383 Engines'

YY1 said

IIRC, de-rating of A body 383 was due to more restrictive exhaust necessary for clearance.

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This is supposedly the reason for the HP derating. Just look at the 383 "A Body" exhaust manifolds compared to a Road Runners exhaust manifolds. My 68 Barracuda had the Super Commando Tin. Remember that it was the bigger of the two available Formula S engines in 1968. Not that it was the hottest engine for that year, as shown in the original ad posted earlier.