Hi, I have a 94 that I'm going to put 4" exhaust on. I will "shell" the cat so if ever there is a visual inspection, it will be legal. I'm looking for information on 4" mufflers. Is there a difference in restriction/flow rate between the offerings and what is that compared to the factory. I'm looking for less back pressure, lower EGT's and mileage/longevity. I'm not after sound.
thanks

 

My only experience with a muffler on my diesel is the one that came with the Summit Racing kit. It is a straight through design, and for 3.5 years it lasted just fine until I built my stacks and went straight pipe. The entire kit is very reasonably priced.

 

all of the "cats" I've seen on a cummins powered trucks have turned out to be resonators, there maybe a truck with a cat on it but if you have such an animal it will be rare indeed(california emissions maybe)... willing to bet you will find its a resonator, which is basically a hollow muffler or a shell.

the aftermarket exhaust systems typically have a muffler that you can see straight thru, they have NO backpressure because basically it is the same a piece of exhaust pipe.

 

January 1994 and after builds came with cat's (even says so in the owners manual (at least in 1994, but I believe that is true at least for all 12 valves-this one was purchased new in oregon). I had a 97 that I hollowed out and it also was a cat. I can't say for other years, but can speak for the above.

 

I can't say for mine either, as it was hollowed out when I got my truck, and the muffler was replaced with a piece of straight pipe.

 

Correct, 94 to 98.5 Cummins engines came with Catalytic converters that were 3" inlet and 4" outlet and the mufflers were 4" inlet and 3" outlet. Removing my cat years ago netted another 1 Psi boost and about 150°F reduction in EGT.

All aftermarket performance mufflers are of the straight through design. I personally like the MBRP stuff for price, fit and quality. I would however NOT do the 409 stainless again as it rusts on the outside and looks bad.. Stick with the Aluminized builder or full Pro stainless system. For what I paid 5 years ago for mine, you could buy 2 at todays prices. Try the DTR store and Lary will hook you up.

 

After tyring of the straight pipe noise for a couple years I went with one of these.
Very happy with them. They are available in several different inlet/outlet sizes.

http://www.dieselpowerproducts.com/p...t-muffler.aspx