[Chevy454]

From experience, the DynoMax or Pypes crossflow muffler will perform better than the Flowmaster crossflow...on our Camaro that we race in Pure Stock [exhaust manifolds], we started with the factory chambered, went to 2.5" mandrel with Flowmaster crossflow & Dr. Gas x-pipe, then to the Pypes 2.5" mandrel with Pypes crossflow & Pypes x-pipe...picked up each time, and shockingly we picked up well over 1mph when we switched from Flowmaster-->Pypes. 2.5" mandrel head pipes are the key, and tail pipe size is last on the list...as long as the tail pipes are mandrel bent you should be fine with 2.25", as the gases have cooled significantly by that point and don't need quite the volume as up front...