Exhaust ?

Bart2500HD · March 23, 2005

Is the exhaust on a 8.1 and Duramax the same size?

dewfpo · March 23, 2005

Good Question. I don't know about the Duramax, but the 6.0 and 8.1L exhaust components are the same size. Go figure?

DEWFPO

Bart2500HD · March 23, 2005

If they are the same size, would a cat-back system for a Duramax provide the same benefits on the 8.1?

Machine · March 23, 2005

If they are the same size, would a cat-back system for a Duramax provide the same benefits on the 8.1?

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They are 3.5", but the goal of a less or non restrictive exhaust on a diesel is to lower exhaust gas temps which aids in keeping the turbo cooler. In addition, most aftermarket diesel exhausts consist of a 4" pipe and a straight thru muffler. Put that same application on an 8.1 and you will loose all of your back pressure. Also, diesel engines do not produce a manifold vacuum like gassers, so I'm not sure what the outcome would be - but I bet it would be a loss of power.

Bart2500HD · March 23, 2005

Thanks!

dewfpo · March 23, 2005

Gas engines need a little bit of back pressure in the exhaust otherwise they loose noticeable low end torque. Mileage can also go in the crapper because of this. An exhaust system really needs to be designed for the engine you have and the operating RPM range you use so that it can enhance and not hurt performance. That means dyno tests over a broad rpm range to be compared to stock. It's too easy to hurt you performance by messing with an exhaust system.

Diesels on the other hand are different beasts. I understand they like no back pressure at all.

Now I don't know if you supercharge or turbocharge a gas engine if it behaves like a diesel.... i.e. doesn't need any back pressure in the exhaust.

Wiser minds than mine need to comment on this.

DEWFPO

Bart2500HD · March 24, 2005

My problem is that my tailpipe is bent and it melts my mudflap. There are no muffler shops here that have 3.5" pipe to make me a new one. I called my Chevy dealer to se about getting a tailpipe and the parts guy told me that you have to buythe whole system from the cat back and it is over $1000!

dewfpo · March 24, 2005

Seems to me that a good muffler shop could cut off the bent section and weld on anything (aluminized) 3.5" or up. Like a piece of 4" pipe for a diesel. The stock system is SS to the muffler, from there on back it's aluminized steel.

Have you thought about wrapping a tow strap or chain around the tailpipe and pulling forward while anchoring the chain to a tree or something. I have done this before and it's worked pretty well at bending the pipe backward towards the near stock posiiton. Doesn't cost anything to try, just go slow.

DEWFPO

bobby5 · March 24, 2005

Seems to me that a good muffler shop could cut off the bent section and weld on anything (aluminized) 3.5" or up. Like a piece of 4" pipe for a diesel. The stock system is SS to the muffler, from there on back it's aluminized steel.

Have you thought about wrapping a tow strap or chain around the tailpipe and pulling forward while anchoring the chain to a tree or something. I have done this before and it's worked pretty well at bending the pipe backward towards the near stock posiiton. Doesn't cost anything to try, just go slow.

DEWFPO

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What are mufflers like flowmaster and such made of. I know its aluminized but is it made from the same material as the stock muffler or will flowmasters rust easier?

Bart2500HD · March 24, 2005

Seems to me that a good muffler shop could cut off the bent section and weld on anything (aluminized) 3.5" or up. Like a piece of 4" pipe for a diesel. The stock system is SS to the muffler, from there on back it's aluminized steel.

Have you thought about wrapping a tow strap or chain around the tailpipe and pulling forward while anchoring the chain to a tree or something. I have done this before and it's worked pretty well at bending the pipe backward towards the near stock posiiton. Doesn't cost anything to try, just go slow.

DEWFPO

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I thought of that. Maybe have to give it a try. On the other hand, I could try to yank the whole thing off so I have an excuse with the wife to put a Magnaflow on it! LOL!

I didn't realize it was bent until I did a Carfax report on my truck AFTER I bought it and found out that it was in an accident with a guardrail.

I love this smilie!

Machine · March 24, 2005

Diesels on the other hand are different beasts. I understand they like no back pressure at all.

Wiser minds than mine need to comment on this.

DEWFPO

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You're right, diesels don't really like back pressure, and they don't produce back pressure (manifold vacuum) on their own. The only significant backpressure a diesel encounters is caused by a chambered muffler and/or a restrictive pipe diameter. The muffler and diameter of the stock Dmax exhaust were designed to produce nominal performance - acceptable egt's and a silent exhaust note. Replace that stock system with a bigger diameter pipe and a free flow muffler and the results are 150 - 200* cooler egt's and a little more HP. The only thing that could be considered a negative aspect of the new exhaust is the rumble coming out of the back end of the truck

sxmax · March 24, 2005

Most exhaust shops in my area have access to mandrel pre-bent tailpipes for your application in 3.5 and 4 inch. I just got a 3.5" IMCO mandrel bent tailpipe when I put my magnaflow in and they also had other sizes from the muffler back. It was only $60 for the tailpipe. Cause like your shop, mine could only bend up to 3"