New stainless bolt-on tips. I have a pair of them, $35 each or $70 for both.
They fit pipes sized 2.75" to 3.5". Obviously you can do some customizing to fit other sizes.
The overall length is 14", the inlet is 3.75", the outlet is 4.5"
The tip is resonated and large which will generally improve the sound in every conceivable way. It will reduce drone if you have it. You may technically see a minor power gain too...