Ok, I know people don't like straight stacks because they are too noisy (hence why I'm getting a Tri-Pac so i don't have to idle and keep you fellow drivers up all night)

But I'm here to talk about MPG gains.......

I recently needed to replace my muffler due to rust. I was going to put another Donaldson on it when a buddy of mine told me he had a 6" bull-turn off his KW just sitting in his shop. I took a look, gave him $50 and a case of beer and off I went.

Had to buy a 5 to 6 adapter and now it has been on the rig for 2 months. It is not too loud and the fact I pull a tank probably helps since I'm not resonating off a trailer bulkhead.

Anyways, i do the EXACT same run every week. Same weight, same roads, same speed, everything. I was getting 8.5mpg on average before, but after I swapped out the exhaust, I have gone up to 9.0-9.2 avg so far for the last 9 runs I have done. I honestly didn't expect this...... did anyone else?

Just wondering if anyone else has experienced a gain with losing the muffler?

Kiddin me???? I'd sleep like a baby next to that sexy sounding diesel.

Throw around fifty dollar bills all you want to Mr Clampet but you should at least make em put forth effort for free beer. Flip coin at least....geesh! :lol:


The gain in mpg's is probably due to less back pressure if I had to guess. I don't think the dot is gonna like it much. The scales in MD gave a friend of mine a hard time because he had a resonator not a muffler. They couldn't see the resonator or something like that. Never know though the dot might not ever say a word to you about it.

Well i got to drink the beer too, so it was ok LOL

As far as the DOT, I have pre-Pass and luckily I have not gotten a red light in a year...... but lord only knows.
It is a '98 spec engine so maybe they would take it easy on me since it's pre-emissions HAHAHAHA Yea right. Oh well, like I said, it's no louder than the new Cascadia daycabs with the Urea motors (damn things sound like a freight-train)