Muffler options ?....

How much power are you making, then how much are you killing with the exhaust pipe diameter and or muffler choice.

2 1/2 is good for around 400 and something hp. Open pipes, 480 tops if that.

Take a 1 5/8/ 1.62 primary run of the mill header, multiply that by 1.8 and what do you get? 2.91 or something? The next closest pipe size is what you should run by the formula, however people have anything from 300-420hp on average and therefore a 2 1/2 is fine or enough and or in most cases , peoples combos are a lil skewed on average, so smaller sometimes gives more under the power band, aka under the cam range.

Hp and exh primary diameter you're running or will be, always figure those in as well as the variables of the combo. Science it out, dont overlook the basics.