What size is the OEM down pipe? Do we benefit from changing the down pipe? Or is everyone just removing the four bolts and putting on a down pipe exhaust system. There is not much price difference, just wondering for the future. Who has the best deal?

The OEM downpipe is 3.5 inches, and is squashed to fit between the Duramax and firewall. There are no aftermarket downpipes available.

here is a down pipe...I know its at RPM Outlet and many have voiced bad experiences with them, but I personally have had good luck with them.


http://www.rpmoutlet.com/duraexhaustm.htm

that's not the downpipe

Yep, Diesel Power is correct - the ring flange on that pipe connects to the downpipe. Here's a downpipe - there are no aftermarket downpipes and there won't be without the special turbo connection and pounding the crap out of the firewall with a sledgehammer to make clearance.


http://www.dieselplace.com/forum/uploads/IdleChatter/2004-10-03_054657_turbodown.jpg

oh damn..thanks for the info... why are they calling it a downpipe? geeez


thanks guys

Many aftermarket items are listed as "turbo downpipe" or "turbo back" which is misleading. They all connect at the ring flange of the factory turbo downpipe. Caveat Emptor. And the Dieselplace will set you free!http://www.dieselplace.com/forum/smileys/smiley17.gif

Next project when I get back off the road in Nov is to make a BIG
downpipe for my LLY. I don't know about the LB7, but there is enough
room behind the motor on my 04.5 to step up at least 1/2". maybe as
much as an inch. Time to buy some bends and straights.http://www.dieselplace.com/forum/smileys/smiley1.gif The LLY benifits from a much simpler flange area. Tranny dipstick is in the way.

This guy <span ="bold">abbo7 claims they do make one. Made by </span>mbrp exhaust.
Edited by: hoot

What size is the OEM down pipe? Do we benefit from changing the down pipe? Or is everyone just removing the four bolts and putting on a down pipe exhaust system. There is not much price difference, just wondering for the future. Who has the best deal?


Not sure of the terminology, so I'll make it up:


Turbo downpipe - Goes from the turbo exh hsg to a flange near the starter and iterminates at a pipe clamp. To the best of my knowledge, these are NOT available. When I cornered people who claimed to make a "turbo-back" system, they really mean from the pipe-clamp back. There is significant deformation in this pipe to clear engine components.


Intermediate pipe - On cat equipped vehicles, the cat is welded in here. It goes from the turbo downpipe to a 4-bolt flange about where the passenger door handle is. It's 4 feet long, and is 3.5" end to end. I purchased a Dynomax pipe, which is 4" IN THE MIDDLE ONLY - http://dieselplace.com/forum/forum_posts.asp?TID=10364&amp;K (http://dieselplace.com/forum/forum_posts.asp?TID=10364&amp;KW=dynomax) W=dynomax


Catback - Bolts to the intermediate 4-bolt flange, contains the muffler and the tailpipe. 3.5" all the way down.

looking at the downpipe schematic posted by idle_chatter, if you flatten a bigger pipe, you will gain cross sectional area and flow even if its flattened: wish I could draw a diagram here. If the stock one is 3 1/2 flattened to 3, it ends up slightly oval shaped. In comparison, if you flatten a 5 inch down to 3 you end up with a much bigger oval, with much bigger cross sectional area...





Assumption I'm making is the size restriction is only in one dimension, i.e. motor to firewall, not side to side as well.

Sadly, it is more like 3-1/2 flattened to 2".

ouch- sounds like my old downpipe! You would think they mighta learned something over the years...

Well, bottom line is that a legroom, a heater and airconditioner in the passenger compartment is more important that a big honkin' turbo outlet pipe. What the heck, with a cat and a severely restrictive "oil drum" OEM oval muffler, what's a big downpipe gonna get you?http://www.dieselplace.com/forum/smileys/smiley18.gif

MBRP does make a down pipe. When I got my exhaust, it was not
available. It was supposed to be avail this past summer.



Look up MBRP (member of this forum) and PM him. Should have info on it.



On edit, turbo back.


Edited by: Max Owner

You know if you guys are worried about clearance because of high temps on a 4" custom down pipe i think there is an easy fix. Have any of you heard of heat tape[i dont know if thats the real name.] It is basicly a thick high temp cloth. It looks like a heave duty tie down strap. Its wrapped around the pipe to keep the heat inside. And you could wrap an aluminum heat sheald on top of that just like the banks 4" turbo down pipe for the 6.0L power stroke. I think this would work great and would love to make a custom down pipe for the truck. I think with a little ingenuity it could happen.

you could also just have it ceramic coated................not a cure all but it would help

I forgot to mention that thanks, so anybody gettin some ideas yet?

fyi, if you have a 3" body lift there is plenty of room for a larger downpipe. not that i recommend a body lift though.

Here are a couple drawings of the LLY's turbo pipe setup from the SI manual.

The tight area to the firewall runs from right at the apex of the elbow exiting the turbo to the top mounting tab. The Oval section appears to be about 4"x2". My rough guess is 1" of clearance between the firewall and heat shield. Can't get a tape measure in there real well, but it looks to be about 3" dia at the elbow. Smaller than I would have thought.

Time to get out the 'small' hammer and work your magic on the firewall there, Fingers. . . ):h

I sense I'm getting a bad reputationn....:)

Just a small cult following. . .):h

I am sure that a new turbo/downpipe will be offered........many companies have been working on this for a while and I believe Clint at ATS is running a larger turbo.......

So we shall all have to wait and see,

T;) NY