Exhaust restriction on my big Dodge
 

The original equipment exhaust finally crapped out on the 03 Dodge with cummins. After a bit of research I bought a "cat back" system from Gale Banks. the original equipment pipe was 3.5", the new is 4" d. I took it to a local shop to have it installed and when it was all said and done they had cut away about six inches of the exhaust and welded in a 3" d. section to attach the 3.5" to the 4" system. The joint is right under the feet of the front seat passanger. It turns out they only had 3" in stock so they stretched it on one end to slip in side thenew 4" and slipped it inside the 3.5" to weld it.

Drat! Why is it that exhaust system people have so little idea of how a system flows?

So now I have a 3" long 3" diameter restriction in my brand new high flow banks exhaust.

Anybody have an idea what the will do to my flow?

(The new system sounds wonderful).

Tell them to fix it correctly. If they whine about it, say that payment on the credit card/check will be stopped ASAP. I have no sympathy for people who do crappy work.

No excuse for that. The work was done by idiots.

They offered to change it on the spot but I did not want to wait, being hungry and having already spent two hours at it.

the welds were beautiful.

I plan to get a piece of pipe for them to use from Gale Banks. they should have supplied something to hook to the existing pipe or tried at least to sell me a new front down pipe.

Don't know what it will do to your flow, but can tell you my Duramax pulls harder and has lower EGTs with my 5" turbo back exhaust!

The cross sectional flow area at three inches is so reduced I would expect leaving it in may almost act as a choke reducing the new advantages or a portion of them . The three and a half to four inch adapter is a requirement. A three inch pipe only has about half the actual flow capacity at a given pressure of a four inch pipe.

Area of a circle is pie x radius squared so 3 inch is 28.26 square inches of flow area where the four inch is 49.24 squared inches of flow area. Almost double as I mentioned.

Did they offer to replace it before or after you saw it?

4 inch
 

Hey Tom....

Drive down here and I will hook you up with an exhaust shop that can do a 4 inch straight pipe for you. Probably cost you more to drive down than the exhaust. Bring a trailer and buy my ponton while you are here.

The shop guy is a big Cummins fan and he runs 4 inch straight pipe to behind the wheels and turns it out to the passenger side.

After.

Well you Did do a cat back system so depending on the down pipe size you still may have a restriction exhausts up stream

Yeah, I'll prolly end up replacing the down pipe with a 4" too.

With the 4" and what looks like a glass pack it is much quieter than my old system which had an actual glass pack. I imagine my old glass pack had lost all its glass packing.

Lovely bass sound now.....deep and cottony.

Why did you need a "cat-back" system, your truck shouldn't have a cat, unless it started life as a NY or California 235 HP truck, and that was for the '04 model year. The engine pipe on that year is 3.5" to the muffler, and 4" from thereon. If you wan't to use a 4" engine pipe, you'll need the exhaust adapter from an '04.5-'07 truck with the "600" engine and catalytic converter.

The biggest restriction in your exhaust is the turbocharger, its outlet is about the size of a golf ball. This is what you want- note the size difference of the turbine outlet, and it's also a dual volute.

not to get on a tangent
 

I saw an 04 Dodge/Cummins truck for sale today that had over 415k miles on it. Guy is asking $3200.

What caused the OE exhaust to fail? I'd like to do something lighter and louder on my 300D, but I can't seem to bring myself to cut up a perfectly good original exhaust system.

Well, they don't last forever. If you want a bit of growl, remove the rear muff and replace with a custom bent straight tail. I have done this many times on benzes. If the muff is good I remove it and reinstall when I sell the car.