Inliners International Forums General Discussion Hi Performance 12 port

What I think is "asleep at the switch" is that the GMC made 4 different heads, and all bad.
Even if keeping the siamese ports and same manifolds, a new head using the 1949 chamber design (Cadillac 331, Olds 303 with closed quench chamber, angled & parallel valves) would have improved power and mileage. None of the GMC 12 port heads do this AFAIK.