the standard Pontiac cast "log" manifold actually flows better than many people might think - the same units were used on non-Ram Air GTO's that made 350hp.
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1970 Formula 400 Carousel Red on black (std) interior "no drivetrain option" car (same base drivetrain as GTO) 1:411 1970 Firebird Formulas originally sold in Canada
that's why I was thinking going to the 21/2 inch repro, plus when every bolt breaks in the head and I have to lift the motor up to change gaskets then its a perfect time to update it.
As usual Ray is bang on with the way exhaust was set up for 75 and 76. It was even that way on police interceptors which serious hampered their performance. Getting back to the exhaust manifold questions: I remember driving a 1973 Laurentian with the 455 interceptor. The clearance was super tight for the exhaust manifolds, combine that with an engine that had a tremendous amount of torque and you had a recipe for cracking manifolds. If you kicked it down and it jumped back in 1st the manifold was done.
