That depends on what you are after. I wanted something that flowed more that the engine could put out, yet not too loud. I think I got exactly what I wanted with a 51" Donaldson Truck muffler. Plenty of flow, deeper sound than stock, no drone at all, and very pleasant all around. If you want louder, go with a shorter muffler. If you search around I'm sure you will find the information you need. You can check out pics of my setup in my readers rig gallery. New tip should be on this week.