I crawled under my new 6.7 today and was looking at the exhaust system,
the last canister before the tail pipe, is that a muffler or a resonator ?

 

The one right before the axle? It's a muffler.



This is a pic of a muff delete...



Don't waste your money...

 

what was the benefit of deleting it ?

 

Well... in the 5.9's, it made it a lot louder and reduced EGT's. On the 6.7... better to hold 120 bucks in your hand and set it on fire. At least you'll feel the warmth that way.

If you want to alter the exhaust at all, I reccomend deleting the whole thing. However, I do not know who makes a code free delete kit yet.