Delete muffler on Duramax/Allison

QUIKAG · December 23, 2003

My brother has an '03 2500HD with the Duramax/Allison combo. For Christmas, I wanted to take his truck over to the local muffler shop and have them weld a straight pipe in place of the muffler.

Who has done this? How much louder is it under load and just cruising down the highway? Is there a noticeable power increase? This is a good, cheap mod for a diesel engine right?

Please edjumucate me on whether this is a worthwhile mod/Christmas present.

Roofer · December 23, 2003

Performance wise I am not sure, but it helps the EGT's a bit. It is a tad loud at 2000 rpms. This is at about 70 for me. It seems to quiet down before and after 2000. Sounds like a Jake brake of a big rig!

If he likes it quiet, I would suggest not doing it and get a full exhaust system with a muffler.

QUIKAG · December 23, 2003

He had a dual exhaust with flowmasters on his old '99 5.3L Z71 truck, so what is the volume level inside the cabin compared to a V8 gasser with flowmasters?

Is the volume crazy loud? How is the tone, is it somewhat pleasing to the ears? He drives around a fair bit unloaded, so it won't be roaring along under heavy throttle all the time. Also, he rarely drives 70mph, so his rpms on the highway are well over 2000rpm when conditions are clear (read: no traffic or cops)

Also, doesn't it help miles per gallon?

manytranny · December 23, 2003

Not too bad. Much worse with towing.

I heard one that had the exhaust dumped at the rear axle. No cat. It was pretty loud. Not extremely, but not quiet either.

If he has a cat, there wont be much noise difference...

422 SS · December 23, 2003

Duramax trucks don't have cats.I took the exhaust off of my 03 and didn't notice any improvement in mpg or performance.The truck was very loud,especially in town.I ran around with it removed for about 2 weeks and put it back on.I would take the exhaust off the truck as a test first before chopping it up.I found it much to loud for my tastes.I wouldn't be suprised if a cop would pull you over due to the noise.I would say it was louder than a v-8 with flowmasters.Test's have proven the stock Duramax exhaust flows very well.

QUIKAG · December 23, 2003

422SS,

Did you remove the whole exhaust or just the replace the muffler with a straight pipe?

QUIKAG · December 23, 2003

Well, I went ahead and did it. He loves it. Under light throttle and cruising, the volume isn't bad at all. Under heavy throttle, it sounds great, no resonance, just a nice, loud WAAAAAAAHHHHHHH (deep) sound that only diesels can make.

Thanks for the advice. Best exhaust mod I've ever done to any vehicle for $40.

422 SS · December 23, 2003

422SS,

Did you remove the whole exhaust or just the replace the muffler with a straight pipe?

I took the whole exhaust off from the 4 bolt flange back.Well it looks like you did it and you're happy.Let us know if there is a mileage increase.

QUIKAG · December 23, 2003

I would imagine the volume decreased significantly from what you experienced as there is a lot more pipe and the exit is near the back of the truck on the side.

It's definitely a bearable volume increase. I've done some horrible exhaust systems in my day that I thought would sound good and sounded horrible with major resonance and an unpleasant tone. This was NOT one of those deals.

For $40 you can't go wrong. The consensus from the research I did, my bro might experience a 1mpg increase, which is better than nothing. Of course, he might have a heavier foot now that it has a mean sound.