2" to muffler, 2 1/2" out is one of the absolute best improvements that can be made for the 22RE. The engine breaths soooo much better. What can happen if you leave the stock pipes? Your engine will be working harder trying overcome the smaller pipe to expel the exhaust gasses, wasting precious horsepower. You can find both 2 and 2 1/2 @ any qualified exhaust shop.

Good luck!
<img src="/forums/images/graemlins/kewl.gif" alt="" />

Dave
86 4Runner, 22R-EB