As far as I know, no Pontiac ever came from the factory with 3" exhaust. The 3" long branch are being produced to help out the guys with monster motor 455s in their Birds to keep the "stock" look. I am willing to bet there is a large difference between them ans the 2.3". From what I have read, there is already going to be a large difference in the basic flow between stock and the R.A.R.E. pieces to begin with. The internal designs are supposedly much improved.
