Join Date: Jan 2015
Location: Injun Territory, 'Merica!
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The 2.5" mandrel bent downpipes are mainly marketed to work with the aftermarket 2.45" outlet RA manifolds made by PYPES & RARE. IF you want to go back from there with a 3" exhaust system, you can, but honestly unless the engine is truly putting out near 500 hp at the flywheel, seriously doubt the 2.45" equiipped RA manifold 3" mandrel bent pe system will gain anything over a well designed free flowing 2.5" mandrel bent exhaust system. Many cases, with moderate engine builds, all the vehicle is gaining is the extra weight of the larger diameter pipe.
RARE and Pypes also offers 2.25" mandrel bent downpipes which seal a little better with standard sized outlet RA manifolds as well as stock RA manifolds. For many years I've made my own downpipe stubs from 2.5" mandrel bent J-tube. On two of my keeper 455 HO cars, both are being completed for Pure Stock Drags, & both are running original round port manifolds with 2.5" mandrel bent drops, Dynomax long case Super Turbo's & 2.5" mandrel bent aluminized all the way back.