[Double A]

Considering normal cast iron 4-bbl Pontiac intakes (excluding special applications such as Ram Air), do earlier 400/455 manifolds flow better than mid/late-seventies manifolds, or are they approximately the same as far as performance goes (aside from EGR or A.I.R.)?

Opinions/info welcome A.A.

[Double A]

Considering normal cast iron 4-bbl Pontiac intakes (excluding special applications such as Ram Air), do earlier 400/455 manifolds flow better than mid/late-seventies manifolds, or are they approximately the same as far as performance goes (aside from EGR or A.I.R.)?

Opinions/info welcome A.A.

[Cruiser]

I believe around 72-73 on up Pontiac started casting some extra material in the carb. bore area to restrict the secondaries from opening fully, I have numerous factory cast intakes(455) and this appears to be one of the main differences between the Pre-smog intakes that I have seen. I have used several H.O. & R.A.IV intakes and the pre-smog cast intakes are very simular to the Hi po aluminum versions,Some differences between H.O. & R.A.IV & cast iron intake are seperate heat crossover for Hi po vs. integral crossover,Weight is also great difference between the two.Really the pre-smog cast intake is a pretty good piece for a mild street build-up on a budget. Given a choice I would use the earlier intake a 69,70,71.

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[Will]

'67 - '72 cast iron intakes are functionally equivalent from a flow standpoint. There are minor differences among them, like the '67 has some funky heat tubes that lead up to the carb base and the '72 has a larger exhaust crossover opening, but the airflow with them is the same. In '73 EGR was added and this carried over for '74. From what I've heard these intakes still flow real well and are the best choice for someone needing to pass emissions inspections. From '75 on up the secondaries were restricted and these manifolds aren't a good choice.