Does anyone know what is the difference between the Magnaflow 15821 and the 16612?
I mean physically, what is the difference?

 

The 15821 is for 2004-05 rigs built before June 1, 2004. The 16612 is for 2004-2005 rigs built after that date. There is a mandreled kink on the inlet pipe of one muffler that is different (or non existant) on the other. My onefiddie was just built last month (3/2005) so I ordered the 16612. Going down to Schucks to get the beefier bolts for the install. The stainless steel bolts that come with the kit tend to snap off before they're tight enough to do any good.