spitfires or manifolds

I don't have any specific numbers but going from manifolds to Spitfires gave my car a noticable bit more snap in the bottom end. I added an X crossover in place of an H pipe at the same time so that may have contributed some as well. (arguable) I was building new 2-1/2' primary pipes for my exhaust anyway so the changeover to Spitfires just fit together. If you have 'em I say use 'em!