4 inch downpipe????

[LowellR]

my truck is a 03 ho six speed dually. i have an edge ez now. bhaf and 51 inch muffler (4 inch in and out) coming in this week. i tow a 40 foot gooseneck racecar trailer that weighs around 12,000 loaded. would it be worth it to replace my 3 1/2 downpipe with a 4 inch. what would be the benefits. it seems like everyone is really proud $$$ of a simply bent piece of 4 inch exhaust pipe.

 

[Gary - K7GLD]

Tough question, and the issue of "benefits" or tradeoffs with a larger downpipe - or one that at least matches the rest of the system - is one that's hard to get reliable answers to. Comparative dyno runs would be nice, but *I* sure couldn't get any when I asked a similar question prior to upgrading my own setup...



I finally decided upon a FULL 4 inch aluminized steel system over a Stainless Magnaflow systen purely BECAUSE I really wanted that 4 inch downpipe! I have NOT been disappointed - with the full 4 inch Rip Rook system, and the Don M 1. 6 F1's, I gained lots of power, and a turbo boost that absolutely FLIES to maximum with the application of throttle. It sure beats second-guessing as to whether the 4 inch was REALLY as beneficial as the 3. 5...

 

[Razkul99]

I am considering doing the same to my truck. I am considering the 4" downpipe and a 42" muffler which is what Mr. Boardman of DRC is running on his desert racing demon. How do you like that big ol' muffler? Any mpg improvement with the less restrictive exhaust?

 

[AndrewKing]

For what it's worth, I went with the 4" downpipe on my truck... . According to Rip the difference between a 3" VS a 4" downpipe is worth about 50 to 100 degrees drop in EGT..... I figured I'd bite the bullet... . If I was going to have the exhaust done anyways, I'd rather not be left wondering if I shoud have done the bigger downpipe... .

 

[Gary - K7GLD]

MY system uses a front Magnaflow SS 14 inch long unit used as a resonance buster, then about 3 feet of 4 inch pipe to the second muffler - a 24 inch long unit. Both are straight-thru design, and provide an exhaust note that is nearly identical to the stock setup, but with far less backpressure. Based upon the way mine functions, I would certainly recommend the 2-muffler setup over the larger single unit - but can't provide any specific documentation as to one actually being better than the other in terms of power or drone issues, other than the fact that mine works well as intended.

 

[MMeier]

I have the 4'' downpipe as well as the whole system in 4". I am running a Magnaflow straight thru muffler that dropped my EGT's 150*-200* in any given situation! Oh, before I forget make sure you get a "MANDREL" bent downpipe, not simply a bent at will piece of pipe that will neck down in the bend underneath, you will be defeating the whole purpose of what you set out to do in the first place!

 

[Tomeygun]

my truck is a 03 ho six speed dually. i have an edge ez now. bhaf and 51 inch muffler (4 inch in and out) coming in this week. i tow a 40 foot gooseneck racecar trailer that weighs around 12,000 loaded. would it be worth it to replace my 3 1/2 downpipe with a 4 inch. what would be the benefits. it seems like everyone is really proud $$$ of a simply bent piece of 4 inch exhaust pipe.

This thread goes over all the thought of why and how much, etc about the swap of the 04. 5-05 cast elbow onto our 03-04 trucks



http://www.dieseltruckresource.com/dev/showthread.php?s=&threadid=62953

 

[LowellR]

ok, you all have convinced me. i am going to get in touch with tommygun and order the parts. thanks.

 

[CLAYTON]

It will still be 3. 5 inches out of the stock turbo and then 4 inches from then on. That is unless you upgrade your turbo which most have a 4 inch outlet then you will have a true 4 inch turbo back system. Right?

 

[LowellR]

i haven't had the part in my hand but from what i understand the outlet of the turbo has a bolted on elbow with an id of 3. 5 inches. the later model trucks had a 4 inch elbow.

 

[SRadke]

i haven't had the part in my hand but from what i understand the outlet of the turbo has a bolted on elbow with an id of 3. 5 inches. the later model trucks had a 4 inch elbow.

This is right on. The cast iron elbow on the back of the turbo is what's 3. 5" at the outlet. The outlet size changed to 4" with the advent of the "600's" in 04. 5.



-Scott

 

[daytripper63]

Isn't the turbo outlet on the 2003 4" at turbo outlet but reduces down to 3-1/2" at the outlet of the elbow that attaches to the turbo?

 

[SRadke]

Isn't the turbo outlet on the 2003 4" at turbo outlet but reduces down to 3-1/2" at the outlet of the elbow that attaches to the turbo?

That is correct.

 

[CLAYTON]

Is it the cast iron elbow that they are talking about or the down pipe after that? I didn't realize that's what they were talking about. So you can swap out the 3. 5 inch cast iron and replace it with a 4" cast iron elbow and get a new down pipe from there... so it will be a true 4 inch from the turbo back?



Mad bad

 

[daytripper63]

So if I went with a B1 turbo (so I can still use my Pacbrake) what if any problems could I see withpacbrake going from 4" to 3-1/2" then exhaust is full 4" from pacbrake connection. I dont want to go buy a 04. 5 pacbrake to get full 4" since I already have this one.

 

[Gary - K7GLD]

I can't help but wonder what other effects might be involved or compromized by casually swapping out the cast turbo exhaust extension for something arbitrarily larger? As much as I appreciate the hoped-for improvements of the downpipe being the same size as the rest of the exhaust system, is it possible the stock turbo discharge pipe in some way provides a smoother, less turbulent transition between the turbo housing/impellers than would be created by an abrupt discharge into a pipe that is not in any way matched to the turbo outlet?

 

[SRadke]

If you replace the cast elbow with one from an 04. 5 now you can have a true 4" system, turbo back. You can even buy a 04. 5 downpipe and clamp from DC to go wiht it if you like. From there go 4" and you've got 4" full length.



Daytripper,

Yes, you can clamp a 03 directmount Pacbrake to a B1 and it will work just fine. The catch is the output of the 03 brake is only 3. 5" so you'll be necking down flow just to open it up again in your 4" exhaust pipe. When I was in a similar situation to you I spent $4xx something and bought a 4" inline brake with hardware that I mounted under the truck. I used my old compressor and wireing to activate it. This opens up the possibility for future upgrades and changes.



-Scott

 

[SRadke]

Gary, the turbo outlet is 4". The newer (04. 5) elbow does provide a smooth transition but rather than necking down to 3. 5" it stays a full 4" through the 45° sweep. Will you see power gains from this mod, probably not but it is still a smooth transition from turbo to elbow. Less turbulent I would guess because you're no longer necking down the flow just to open it up again in a 4" pipe.



-Scott

 

[CLAYTON]

If you replace the cast elbow with one from an 04. 5 now you can have a true 4" system, turbo back. You can even buy a 04. 5 downpipe and clamp from DC to go wiht it if you like. From there go 4" and you've got 4" full length.

Ahh... I see. That's why I love this website. It gives me the ability to ask questions and get answers

 

[daytripper63]

SRadke, according to your sig I have same set up on my 03 less the injectors and turbo. If you were to turbo again would you still do the Killer B2 or ?

Any likes or dislikes? how well is spool