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This project has been on the back burner for over a year. I finally tore into it. I’m not replacing the downpipe yet. It is probably going to have to wait until a new turbo goes on. The main driver of this project was poor mileage. I suspected the soot trap was plugged and choking off the engine.

I took the old exhaust off without cutting or breaking anything. I wanted to make sure I could put it back on if I ran into something unexpected and was unable to put the new parts on. Once the soot trap was off, I tried holding it up to the sun to see if any light came through. I couldn’t see ANYTHING even with it pointed directly at the sun. The first photo shows the old exhaust and most of the new parts side by side.

I did take a video of the truck running with just the open down pipe and will try to figure out how to get it posted later. I also took a video once I bolted up the first piece of pipe and slid the muffler in place.

I was hoping that the first section of pipe could be straight, but after several hours of cutting, tacking, and fitting; the second and third photos show what I ended up with.

The first section of pipe is bolted up and I’ve taken it for a test drive. It ends just past the front of the box. I was amazed that it is not obnoxious to drive this way. The turbo whistle is very noticeable while accelerating and you can just pick it out even while cruising on flat ground. I can clamp the muffler on, but I don’t trust one of my exhaust hangar welds to support it yet. I ran out of rod and had to order more. It is supposed to be here by the weekend.

The muffler is a Magnaflow 12773. Once I get it bolted on I will be within a couple feet of the rear axle and will have to decide if I’m going to order some bends or continue with the section and weld technique I used for the first pipe.

I plan to crawl underneath tonight and take some photos showing the routing. I should be able to get them posted up tomorrow.

I’ll update this thread as I go.
 

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How much do you have into the exhaust?

The down pipe is the main restriction. A diamond eye exhaust system with mandrel bent down pipe is only $260 shipped.
 

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Just add Fuel
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Discussion Starter #3
How much do you have into the exhaust?
The 304 stainless pipe came off the "shorts" rack at the local Steel Mart for $2.50/lb. If memory serves, I have about $40 or $50 in the pipe. The Magnaflow muffler came from Summit for around $140. The 3/8 stainless plate for the flange also came from Steel Mart from the shorts rack at $2.50/lb.

The down pipe is the main restriction.
I dissagree. When the soot trap is plugged, I suspect it is much more restrictive than the down pipe.

A diamond eye exhaust system with mandrel bent down pipe is only $260 shipped.
I thought hard about going with diamond eye. I was happy with their design and workmanship, but am not impressed with their choice of materials. It seems for the 6.5's they only offer aluminized steel exhaust. They do offer stainless for some of their other systems and some of their bends - but even then it is 409 stainless. 409 would have been ok, but I really prefer 304.

And some more pics:
 

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Take a look at your stock downpipe...it is definitely the worst part of a stock 6.5 system. They look like someone ran it over with a truck.
 
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Just add Fuel
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Discussion Starter #5
Take a look at your stock downpipe...it is definitely the worst part of a stock 6.5 system. They look like someone ran it over with a truck.
I've had my down pipe out of the truck. It is not nearly as bad as some that I've seen pictured on this site. It will be getting replaced in the future. I already purchased some 3.5" 304 stainless to start playing with.

I certainly agree that it is restrictive - just not as restrictive as a soot trap with 250k miles worth of soot plugging it up. Just my opinion. Time will tell.

Thanks for the input.
 

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It is a nice looking set up and good call using the stainless steel. It's a good start in the right direction.
 

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Discussion Starter #8 (Edited)
Open Down Pipe

Here is a video with only the down pipe installed. Nothing spectacular. It doesn't sound terrible outside the cab, but it does sound pretty bad in the cab.

Link you youtube.
 

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Sounds nice and throaty. Should sound real good with a tail pipe. Good luck getting it finished up
 

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Discussion Starter #12
Finally getting around to adding a few more photos. I need to get a few more feet of pipe to get the exhaust out from under the truck.

This system turned out VERY quiet. There is a deep growl when accelerating, but otherwise you pretty much don't know this isn't a stock system from in the cab. There is no drone at all. If I were to do it over, I would probably choose a slightly shorter Magnaflow muffler for a little more sound.

The first photo shows the flanges that bolt up to the downpipe. I have 2 plates here. One has a 4" hole for the new exhaust. I might have been able to get this to seal to the downpipe flange, but I decided to put another plate in with about a 3.5 inch hole to make sure I got a good seal. This plate will eventually be the flange for my new downpipe when I get around to making it.

The other photos show as much of the exhast (post muffler) as I can. I had a tough time taking photos with the truck on the ground and I'm too lazy to lift it up today.
 

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Jim, looking great!

That truck is CLEAN underneath. Mine looks like utter hell compared to yours.
 

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Discussion Starter #14
Jim, looking great!
Thanks!

That truck is CLEAN underneath. Mine looks like utter hell compared to yours.
This truck came from Oregon about 2.5 yrs ago. They don't have the salt that we have to deal with.
You should have seen it when I got it! 2.5 yrs of salt spray has made a very noticeable difference even with frequent washing.
 

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Discussion Starter #15
Well, after a few tanks of fuel - I'm conviced that a plugged soot trap was not causing my poor mileage. The new exhaust has moved my mileage from mid 13's to low 14's. At least it sounds a lot better!

The search for improved mileage continues...

Not sure where I'll go next. Perhaps a collapsed inner pipe in the crossover?
 

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Very nice work! Did you replace the downpipe? It looks like you did.

New crossover will help get the turbo spinning better.

Have you checked/set TDCO for the injection pump. Getting near -.5 will help mileage, but at the expense of some power.

Kinda from left field, but make sure your brakes are not dragging and wheel bearings are good.
 

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Discussion Starter #17
Did you replace the downpipe? It looks like you did.
Not yet. I have a piece of 3.5" tubing here for that project, but haven't started working with it yet. I had the downpipe out when I replaced injectors and it isn't nearly as crushed as some I've seen pictured here. It may be hurting power, but I don't suspect it is hurting mileage much. Seems these trucks are able to get good mileage with the factory downpipe.

Have you checked/set TDCO for the injection pump. Getting near -.5 will help mileage, but at the expense of some power.
I have played with TDCO a little and it has not made a significant difference. I'm currently set to -1.76.

Kinda from left field, but make sure your brakes are not dragging and wheel bearings are good.
I've been through the front and rear brakes and everything WAS working properly. I've checked for heat a few times after driving for longer distances and none of them seem to be getting hot. I will probably be changing over to my other set of wheels and tires in the next few weeks and will check things over again. I did notice that in one of my photos in this thread it looks like there is moisture at the right rear wheel - I'll need to check that out closer anyway.

There is some wear in the front suspension that could be causing alignment problems. If this was bad enough to cause poor mileage, I would expect to see severe tire wear - and that doesn't seem to be happening. I'm planning to get this fixed, but it hasn't been a high priority yet.

When I set TDCO (intake off) I noticed that cylinder 8 was puffing smoke out of the intake port for several seconds after startup. It cleared up, but left me wondering if there is a problem with that hole. Planning to do a compression test when I get time to see if that reveals any problems.

Thanks for the input!
 

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Discussion Starter #18
I was doing some clean up in the shop the other night and noticed my 3.5 inch section of pipe standing in the corner. Decided to grab the propane and a hammer and about 15 minutes later I had this:
 

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Discussion Starter #19
I was really surprised how nice it appeared to turn out, so I test fitted the turbine housing to the flare. I don't suspect this will end up on the truck any time soon. Just thought y'all may enjoy the photos.
 

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respect the DB4 5722....
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I was really surprised how nice it appeared to turn out, so I test fitted the turbine housing to the flare. I don't suspect this will end up on the truck any time soon. Just thought y'all may enjoy the photos.
nice work jim, is that your JD schwitzer? you got some nice flowing lines on that system, and stainless rocks for salty conditions.... if you ever try that schwitzer/BW turbo in place of that GM cork, you will see that you chose your muffler size wisely....:thumb:
 
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