With log manifolds and 2 bolt flanges 2 1/4" is usually about as big as you can go.
The RA manifolds have larger flange areas enabling 2 1/2" if you enlarge the center hole in the flange.
There is a way to adapt up to 3" pipes using header collector flanges adapted to the 2 or 3 hole flanges, requires welding and fab skills. Basically the old flange pattern is used to build a plate that is first bolted to the manifold and then has the 3 hole header collector flange pattern on the 3 inch pipe that is then bolted to the adapter plate.
Way back years ago, on the 67 GTO in my middle signature picture I built adapters to adapt the 3 hole Pontiac RA head pipes to driveshaft tubing (3 1/2 inch OD) that dumped at the rear axle. The seat of the pants dyno was feeling the improvement...LOL
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Brad Yost
1973 T/A (SOLD)
2005 GTO
1984 Grand Prix
100% Pontiacs in my driveway!!! What's in your driveway?
If you don't take some of the RACETRACK home with you, Ya got cheated
Last edited by Sirrotica; 05-30-2019 at 09:26 AM.
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