Great job and congratulations to all involved!
The SD 455 is flat out bad azz engine. Created by all the guys whose input over the years made the cars we love today.
Pontiac engineers knew the exhaust was a huge restriction on the SD engines. After dyno tests it was determined the exhaust needed improvement. From what I remember they ran a small 2.25 pipe of the manifold for about two inches and then welded a 2.5 over that tube and 2.5 was used going into two resonators shaped similar to the old "Cherry Bomb mufflers" and then into the crossflow muffler. 2.25 tail pipes were used from the muffler back. For 1974 the same exhaust was used but the resonators were dropped.
This compares to the LS-6 which received 1 7/8 tail pipes.
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