cquestad

Hello all!

I was wondering if all downpipes are a true 4" diameter like the Banks that replaces the cast elbow on the turbo? I want to piece together my exhaust with a 4" downpipe, 4" mid pipe, Donaldson Muffler, and the stock 4" over the axle. The Banks downpipe is what I want in theory, but it is stainless and expensive. I would like a "less expensive" aluminized steel true 4" downpipe and was wondering if there are options....

Thanks!

Vaughn MacKenzie

cquestad I was told by Diesel Power Products that Banks is the only maker of a downpipe that replaces the cast elbow. But as far as I know all the other manufacturers' downpipes are true 4" right off the elbow, I'm quite certain of this.

When I did my budget 4" system I got a PowerStroke 4" intermediate pipe from DPP (Not DPPI) which I connected to the stock 3.5" diameter downpipe and then went to a 4" straight-through muffler. Then I connected the stock tailpipe to that after cutting out the flared piece (that goes from 3.5" to 4" exiting the stock muffler). I also put an Aeroturbine in the system just behind the downpipe (patched into the PSD intermediate pipe).

I was able to do a system for quite a bit less than a full 4" system and got an Aeroturbine to boot. Unless you're planning to run big HP the stock downpipe is fine. If you do go with a true 4" downpipe the PSD intermediate pipe will hook up to it fine. Give Diesel Power Products a call if you want to check into this. There is a recording of my truck with this system on their website: www.dieselpowerproducts.com

Vaughn

(not affiliated with DPP, just a happy customer and they're only a mile down the road)

AK RAM

The 04’s may be different, but the 03 stock elbow is 3.5" at the outlet...hence, so is the down pipe. Turbo is 4" at the outlet, so the elbow would have to go to be a true 4". Just FYI....

cquestad

I believe one of the selling points of the Banks downpipe is that it replaces that elbow with a bend in the downpipe. I guess the downpipe attaches to the turbo direct without the choked down 3.5" OEM cast elbow????

I am just trying to figure out if this is a better set up...4" the entire way instead of a 3.5" choke right after the turbo. It seems like that would flow smoother and reduce EGT's the most...

Tom488

Talk with Diesel Dynamics (http://www.dieseldynamics.com). I installed their turbo kit, and it came with an aluminized 4" downpipe that bolts right up to their turbo, no elbow. Ask them if it will fit the stock turbo.

Vaughn MacKenzie

cquestad, to clear one thing up:

The stock downpipe does not "choke down" to 3.5" because the outlet from the turbo itself is 3.5" and so is the cast elbow.

The 4" downpipes flare out a half inch more in diameter.

Like I mentioned before you will not lose anything by sticking with the stock downpipe unless you're going with big HP and a bigger turbo (say over 350hp at the rear wheels). In actuality if you are going for the smoothest transition, stick with the stock elbow and downpipe then flare to 4" under the truck. It's been shown on 2nd Gen trucks that flaring to 4" right at the turbo hurts low end response but that was more of a diameter jump, going from 3" at the turbo to the 4" downpipe. You get better scavenging by not changing the diameter for a few inches after the turbo outlet.

Vaughn

Push Rod

This is primarily because the 02 and under had a 3" outlet on the turbine side. The rapid change in pipe diameter caused some turbulence in the exhaust flow, in effect causing a restriction. This will not occur on the 03 trucks, as the turbo has a 4" outlet.

Rod

JKE

ROD - vaughn stated 3.5 for elbow and trubo....you stated 4. I have read 3.5 elsewhere also....Is it infact 4"? At what HP does the 3.5 down pipe begin to create a problem?

TIA - JKE

Push Rod

The actual turbo outlet itself is 4". The elbow starts at 4", and then works its way down to 3.5".

Some very early 03's, of which mine is one, actually have a 4" ID cast elbow all the way through.

As for power levels, 3.5" should be just fine right up to 350 or so, unlike the VP44 equipped trucks which really didn't need to look at exhaust until 375HP.

We just started testing with a 5" system, still using the cast elbow and 4" downpipe. Thus far, we've seen an EGT reduction of 300F on the lower power levels of the TST box. It looks as though we're gonna need all the exhaust we can get on these trucks.

Rod

JKE

Thanks ROD!

Vaughn MacKenzie

Heh. . . I have an elbow in my garage . . . maybe I'll have to get out the tape measure and check Rod on this

cquestad

I plan on running a scotty III, Edge EZ or VA, and maybe a piers mod stock turbo...

What I mean by choke is the reduction in the cast elbow from the 4" exit on the turbo to 3.5". Is there enough EGT/HP benifit with using a true 4" downpipe (like Banks) to justify the additional $50-75 cost for this downpipe?

Also...we keep missing my first question. Does anyone know of any other manufacturers that make a true 4" downpipe that replaces the cast elbow (like Banks)?

Thanks!