Diesel experts.

[ChristianPatriot]

There's only so much downpipe you can fit between the turbo and the firewall. I really don't know what the limit is on a Duramax. The outlet of the turbo never changes though no matter what downpipe you get. And even the aftermarket ones that are 3" probably have smoother bends than stock. If you get a 4" exhaust system that say turbo-back than it includes the downpipe.

 

[42769vette]

There's only so much downpipe you can fit between the turbo and the firewall. I really don't know what the limit is on a Duramax. The outlet of the turbo never changes though no matter what downpipe you get. And even the aftermarket ones that are 3" probably have smoother bends than stock. If you get a 4" exhaust system that say turbo-back than it includes the downpipe.

I cant find one that comes turbo back. All of them are down pipe back.

I had never thought about the first restriction being the turbo anyways. I guess I just don't understand having a 3 inch pipe feeding a 5 inch pipe, but with the turbo being the first restriction I would THINK there is no point in putting a exhaust in larger than the turbo outlet.

 

[ChristianPatriot]

Bigger pipes do flow better/more. The best exhaust system is no exhaust system. That's why drag cars run open headers. Of course that's extremely impractical for a daily driven truck. Gotta get the air in and out as freely as possible. Bigger is better.

 

[horsehaulin]

Heat, to disperse spent energy used to drive the turbo.

 

[horsehaulin]

Seriously, PM me

 

[ChristianPatriot]

After checking some Duramax forums, sounds like 3" is all that will fit without modification. But for the intended uses of your truck, I don't think there's any need to worry about it. Just go with a decent DP back and call it good.

 

[jkaetz]

I haven't even seen the truck yet. Its a insurance truck, so it will take my body shop a month to get to the body work, and another few weeks to get it done. All Im going off of is folks on the net saying they get 13 MPG from a stock truck, and 20-25 from a "tuned" truck. 10MPG difference will make the improvements pay for themselves fairly quickly.

I've been a "tuner" for the better part of the last 10 years. I've been involved with multiple vehicles ranging from bolt on parts, to OEM parts from a different model, and tuning. If the auto manufacturers could gain 50% to 100% fuel economy by using a tune or bolt on parts, they would. The simple matter is that those gains are unscientifically thrown out, repeated, and exaggerated by enthusiasts and others who want for a vehicle that is superior to what the manufacturers put out. With experience I can say at most you might gain a 10% fuel mileage boost. Two to three mpg was my real world experience after a free flowing intake, exhaust, and tune. The tune was not a simple buy it off the shelf tune either. It was done by me with my vehicle adjusted over the course of several weeks as I drove back and forth to work. Remember if it sounds too good to be true, it probably is.

I should note that I can usually beat EPA rated mileage numbers simply with my driving habits even on a stock vehicle. This is typically where the large gains come from. Someone wants more mileage so they do all these things AND start driving differently causing a large swing in fuel economy. They attribute that difference to the modifications not realizing that they have also changed driving habits. Get the truck, drive it, do the math at the gas pump not the trip computer, and see what mileage you really get. Then decide if you want to start fiddling. Another thing to keep in mind is that aftermarket exhaust parts typically won't last 200k miles so you'll likely be replacing things sooner than you would with OEM parts. Additionally, 200k miles is a LONG time to recovery your investment unless you drive a lot of miles. Diesel vehicles will easily provide a mileage boost over the equivalent gasoline powered vehicles, but you shouldn't expect earth shattering economy either. The wife and I love our diesel SUV because of the power and economy combination but to expect it to get the same mileage as a car is unrealistic. 20 - 25 mpg is what you'd realistically get from a normal large car that didn't have a 120 HP engine and you're expecting that from a v8 fullsize truck with the aerodynamic properties of a brick.

 

[Caleb]

From my research, DP tuner is the best

Diesel tuning products for Ford PowerStroke

 

[42769vette]

Update:

I got the truck, and the dash calculator said 14 MPG

I put 5" AFE exhaust, 4" downpipe, and a different manifold that the diesel guy recommended (straight manifold??), AFE cold air intake, and 265 transforce tires. The truck sounded awesome, and I loved the power. It averaged 18MPG, and I don't do much HWY, or Interstate driving.

I took it to Danville performance, and Mark did the EFI live tune. I am absolutely floored at the results. I have not played with it a ton, but I think the truck would give my old vette a run for its money in a race (I didn't say win). I now have 5 tunes. I was told

1=wet roads/ice
2=pulling
3=daily driving (he said it should be my best MPG)
4=race
5=for the rare occasion I get beat on #4 (his words)

My dash computer says I got 26.5 MPG from Danville to Liberty yesterday (little over 100 miles). I know the on dash computers are not 100% accurate, but if its close to that, I'm calling this project a huge win. I've never got 26.5 MPG out of a 3/4 ton, 4x4 in my life. The guys at Danville were a huge help. They didn't try and sell me stuff I didn't need, they listened to what I wanted, and tuned the truck for that, and it sounded like a shop full of firearm's enthusiast's, so we had something to BS about while the truck was getting worked on. I ended up with 888LBS of torque which to me is amazing.

 

[Bowman78]

Be careful with all that power.. It can get addictive and pricey if you go overboard... 800+ft-lbs of torque at the wheels is substantial and can greatly reduce drivetrain longivety and reliability..

 

[fordmanchris]

Check out ecomodder.com there's a guy on there i believe from Indiana that is getting around 50 mpg out of his truck with simple stuff. He has a cummins but most of the mods he did should translate over.