First off, the mufflers MUST flow as well as a 2 1/2 inch pipe to make a 21/2 system as efficient as it can be. Pretty symple, right? Easy to forget though. A very well designed 21/2 system should allow a full 500 hp with zero loss. But looking at flow charts, percentage of loss as you go above 500+ will start small, but rise rapidly, choking a 700 hp motor by about ten percent, or 70 hp. A good 3 inch system looks like it would allow 730 hp with out any loss. At 800 hp, the loss looks to be about 2 percent, or 16 hp. All this assumes a very well designed system.