3" is too big for the everyday 400 motor. Trust me on this. I have a dual 3" setup with a 9.7-1 67 670 headed 400 est. 300 HP motor and it was overexhausted.
Same motor, same rear gears, same trans, different exhaust 2.25 vs 3"
Thats why I said run restrictive mufflers if you are left with 3" and have no other option.
The motor ran like crap and all that was changed was exhaust from one car to another.
Zero or minimal back pressure is not good for a Pontiac.
Si Vis Pacem Parabellum
1967 Starlight black PMD Engineering 400 Auto 1968 Alpine Blue 400 4 speed 1968 Verdoro Green 400 HO 4 speed 2013 1LE 2SS/RS Inferno Orange Camaro.
