'01 downpipe on '04

DmaxMaverick pulled by today and brought the original downpipe for his '01. He's since gone with a Kennedy exhaust so had this bit which would be a big blessing for mine if it would bolt up to my exhaust. Well, it did--and it is--and my Duramax now has no catalytic converter!

I was on the ground already replacing the shocks. Greg brought some tools that made that a lot easier, too! But this downpipe was pretty exciting I gotta tell you. My '04 is a crew cab, his '01 is an extended cab and laying the pipe under the truck it looked like a direct bolt-on replacement for the catalytic convertor. Turns out it was! Simply unclamp the '04 from the turbo, unbolt from the flange on the downstream side, and remove the bracket for the hanger. The cat downpipe is a little tricky to snake out of there but the '01 w/o cat slips right in its place. We're talking perfect fit!

Not only is the catalytic converter gone, so are a lot of crazy twists and turns GMC put in there to accomodate it. Now the exhaust comes straight down from the turbo and makes an easy sweep back towards the straight-through muffler. It's not a 4", not Kennedy, or Banks, or MBRP, but it is a drastic improvement over what came on the truck.

Thank you, Greg! :cool:

Your welcome, David. It wasn't a bad job, at all.

Just for clarification, it wasn't the "downpipe" we replaced. The downpipe, to many, on the Duramax trucks has become somewhat of a misnomer. The pipe we replaced was the first section of pipe, after the downpipe, between the downpipe and the muffler section flange. Also, this was on CA trucks, so it's probably unique to CA trucks (CA began emission equipment in 2002 on LB7 engines, EGR and Cat). I've had very limited exposure to non-CA trucks, so I can't say for sure. It seems all accommodations for chassis variations are made on the rear tailpipe/muffler section, leaving the forward pipe the same for all (or at least most) models.

The pipe replacement was an exact fit bolt-on. The V-clamp flange and the rear flange matched up, as did the hanger, and all angles were correct. It was a PITA getting out the original pipe, as David said. The hanger bracket had to be removed to allow the Cat room for passage. A bit of twisting and maneuvering and it was out. The right front corner was jacked up, and the wheel and wheel well liner was removed. While it wasn't required, access was very good with the wheel and liner out of the way. The V-clamp is behind the liner and can be accessed by bending the plastic liner, but it was much easier and a straight-on shot at the loooong threads (used an impact driver with deep socket for R/R of the nut). It also helped leaving the rear flange loose to line up the V-flange. David's original gasket at the rear flange came out unmolested, so it was reused. Having the front raised allowed a bit more room getting out the original pipe.

And it should be noted (the disclaimer), this modification is intended for "off highway use only". Of course, we would never modify a mandated emission system for use on CA highways.

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Originally Posted by DmaxMaverick

Of course. . .

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Of course!;)

Thanks for fleshing out the description of the swap. You are great with details, and those points work together to make the difference between a job gone smooth and successfully, and a major pain. What I saw yesterday was smooth, right down to the clever tool for removing the wheel well liner fasteners. Gotta get me one of those!

There has been very little change in the sound of the truck. I don't care for a loud exhaust, and with the catatonic cnvertor gone and a straight-thru the tone is still mellow and aybe a touch more throaty. Very happy.

The biggest difference I can see is that the EGT drops WAY faster than it did with the cc installed. I've got a cool-down timer set at about 350F and used to have to wait a goodly time for it to get down there before it shut off. Not so any more. . .

Thank you again for all of your help, Greg. My truck has benefitted so much from knowing you, and hell, I just enjoy working with you whatever we might be fixing up.

David