But now we need to think about the exhaust system. Improving the exhaust system is number one as far as freeing up usuable power, it doesn't "make" any at all. But the factory needed a quiet, smooth, and responsive engine because the driver might be a little old lady going to the store in Hawaii, or a young fellow driving around at 5000 ft altitude in Colorado. So they compensated for this, and for ground clearence on some vehicles.

The best setup cost wise we have found is to use the excellent factory exhaust manifold, then increase the pipe size to 2" all the way to the muffler, yep, the cat, too. Then we increase again to 2 1/4" on exit all the way back.

This creates a bit of directional flow and frees up power, it fairly quiet and smooth.