After searching for many weeks for a used DPF to gut out, and not finding one, I decided to just build a straight pipe and finally install my tuned ECM from Nick at Duramaxtuner.

Nick spent the time to talk to me and understand what I was looking for in my tune. All I wanted was fuel mileage...I didn't care how he got it and didn't want a bunch of HP either.

With the ECM installed and a couple thousand miles travelled I can report a solid 2 MPG increase, cooler EGT's, slightly higher boost, a more lively turbo sound, smoother throttle response, and lower load numbers on my DashDaq.

Payback will be under 6 months for the money I have spent. I am hoping that without the re-gens that my used oil analysis will come back from the lab with much less fuel dilution. I am also hoping that once we return to summer fuel, my mileage will be up 3 MPG.

I left my cat in, to act as a bit of a muffler and to clean up some of the smoke (and even if I floor it, the truck does not smoke with the DPF gone now).

Did you make your own flanges or just cut off the remaining flanges in front of & behind where the DPF was?

A full 4" turbo back could give you another 1 MPG increase.

Not wanting an argument, and I can see how a exhaust larger than 3.5" would help with maximum power, especially on a truck that has the non-derated Duramax, but how would the 4" exhaust help much with cruising fuel economy? Isn't the backpressure already very low in a 3.5" system under cruising conditions? And isn't the turbo downpipe the next most restrictive part of the exhaust after DPF & Cat are gone? (though PiperOne still has the latter).

When I went 4" turbo back no muffler/cat I picked up 1-1.5 MPG. I did not pick up any MPG gain when I put on the Diamond Eye turbo direct pipe.

So the first change was from stock 3.5" exhaust with muffler & cat to 4" with no muffler or cat?

And the second change was the turbo downpipe (or direct pipe)?

That would be correct.

I made my own flanges from 1/4 inch plate, and welded a piece of 3 1/2 inch pipe in. You need to weld at a very small angle between the flanges and the pipe (ie not square) but its not hard.

Further exhaust mods will have to wait until the warranty is done. In 25 minutes, I can be back to 100% stock for dealer visits. As busy as I am, warranty should be all gone by July. The cat is also acting as the muffler now (truck has no muffler from the factory).

I made my own flanges from 1/4 inch plate, and welded a piece of 3 1/2 inch pipe in. You need to weld at a very small angle between the flanges and the pipe (ie not square) but its not hard.

Further exhaust mods will have to wait until the warranty is done. In 25 minutes, I can be back to 100% stock for dealer visits. As busy as I am, warranty should be all gone by July. The cat is also acting as the muffler now (truck has no muffler from the factory).

Yeah, I discovered that it was almost impossible to get flanges for 3.5" pipe.
I measured the offset between front & back DPF pipes to be not much more than an inch.

re: "Further exhaust mods will have to wait until the warranty is done"
Yeah, I feel the same way for now. Since my neighbor (who works at a shop with a water-jet cutter) has agreed to make some flanges, I think will just delete the DPF for now. Since 3.5" pipe is an oddbal size (nobody around here has it)
the Flo-Pro 8880 muffler
http://www.flopro.com/heavyspecs.html
is fairly unique in because it is long enough to replace the DPF without having to extend it.


BTW, if you look at this thread,
http://www.dieselplace.com/forum/showthread.php?t=435785
I posted a few pics of pickup exhaust systems that thanks to the experience of ShopSpecialties & ramjammx, we know for sure will work.
The Diamond Eye & ANSA Silverline are two that don't have an extra un-needed bend (e.g: Corsa)

You are already running EFILive so there goes your warranty if GM does not want to cover something.

I have the original ECM..un molested for warranty purposes. Tune is running on a separate ECM. 4L85E TCM's do not record the switch like Allison TCM's do.

Nomad, try a big truck shop parts place (like a Vipar or HDA affiliate)for the pipe. 3.5 for some reason is common there, I bought a Nelson 36" length of it in stock for 30 bucks.

You are already running EFILive so there goes your warranty if GM does not want to cover something.

I've got a spare ecm. Original ecm is untouched. Actually original ecm is still installed in van as of now.

They won't notice last regen was a long time ago if original ecm is back in long enough before taking back in for service. And even if no regen occurs since original ecm is swapped back in, they'd have to notice it, which wouldn't happen for most service work.

I like it quiet. I think I'll go with the Flo-Pro 8880 3.5" muffler. That way I can do a cat delete later (using an old LB7 front pipe, that a guy about 50 miles from here supposedly has) and still be reasonably quiet.

If I do Quigley conversion next summer, I'll need the pickup truck exhaust's zig-zag ahead of the rear-mounted muffler, because the Quigley conversion adds another cross-member in the same location as a pickup truck.