I am about to pull the trigger on quite a few upgrades and some may consider downgrades for my tow rig. I had a question about others actual experience with downpipes. Stock is a 3" and i have a new one. My question is does a 4" downpipe fit well? I cant wrap my head around it will actually show a difference in my slightly upgraded application. I am going to wrap the pipe with header wrap to help cab temps a bit. I've seen the difference that makes on the cab floor. My thought process is if a 4" is the same EGT or even a 50* drop it would be more beneficial to me if the pipe was not quite as close as to the cab with the 3". Of course money is on the table to the tune of $300 difference to get a 4" back from the turbo outlet vs 3" to 3.5" to 4" is how I would hook it up for no money out of pocket.

For complete transparency- I will be adding a Banks Brake. I bought this one brand new never installed from someone for basically a song and dance. Nowhere near retail. Original purchaser had the complete power package on an 03 and it rusted away from under him before he ever installed the Brake. I've wanted one for 20 years and I finally ran across a deal.

Any experience with downpipes and their fitment would be well received and appreciated! Thank You in advance!

 

If you are interested, I have a MBRP 4" downpipe from when I converted to a T4. It really fit well. Private message me if interested. You pay the ride...it's yours.

 

PO put 4" in mine. It is tight but it fits. Just make sure it clears everywhere and isn't rubbing on anything before you tighten it into place. Otherwise, you'll be back asking what that rattle is.

 

I was under the impression, and I may be wrong, but doesn't the "Banks Brake" replace about half of the downpipe with a giant cast piece that bolts to the original outlet flange turbine housing? If that's the case, a stock or stock replacement discharge pipe won't fit anyway.

 

Yes it does. The Brake kit comes with one of two pipes: it either hooks to a 4'' system or hooks to the stock system. The stock downpipe is 3'' tapered to 3.5''. The kit I have came with the brake downpipe to attach to a stock exhaust system.

 

Incredibly kind and I appreciate that, however I cant use a stock style pipe because of the brake. Thank you just the same.

 

Yes sir. Thats what I know. That means its that much closer to the firewall no matter the arrangement right? So my theory of a stock sized downpipe, wrapped, would be better at keeping heat from the floor. (i.e. more air gap) ??

 

4" DiamondEye here, wrapped everything after the exhaust headers to the bed as well. 4" is pretty tight, not sure how some did the 5" without it touching block and cab. If you go with a mandrel bent 3" it would probably be a slight improvement over stock. 3.5" mandel bent would be easier to install than 4"

​​​​​​
Just depends on your future turbo mods plans to which course we'd recommend

 

I installed an MBRP 4" exhaust system which included the down pipe. It fit well, but I installed the turbo before the down pipe due to an amateur mistake. I spent quite a bit of time getting the 4" down pipe in there, but it fit well. No rattling, no contact, no concerns.

That said, I installed a 3.5" Carson Stauffer Diesel 3.5" down pipe in 2018 as part of the T4 conversion kit and it fit just as well. Some others had issues, but that was with the angle of the horizontal output at the bottom. I had zero issues with the 4" or 3.5" fitting properly.

The stock down pipe is capable of flowing more than you are looking to put through it and going to a 4" would gain you nothing other than being able to say you have a 4" exhaust. If your exhaust is rusting or damaged, by all means go to 4", but don't because you think it will be better.

I hope what the fellas and I have said gives you some clarity in your decision making process.

 

I wouldn't have said anything about it if that information was given beforehand.

 

I thought you'd never ask: I plan on either a KC balanced assembly OR a 63/68/84 and 160/0 injectors. I have a hydra. I am a 6 speed. 4.10 gear. dually. Dedicated tow rig (i wanted the 160/0 because if Im in the west end of nowhere I can probably get a 160/0 better across the counter incase of failure). HPX from riffraff. AIS intake with ZOODAD mod. (really really helped my truck! In 100 HP PHP tune I could bury the filter minder. After those 2-2'' holes for the intake my filter minder never moves.)
I am adding a fuel pressure sensor (just ordered all my stuff from riffraff to upgrade my CTS2). Might add a 203* I'm not sure yet.

 

Somewhere. Sometime. I cant remember if it was in an old Powerstroke Registry or a forum somewhere but I read an article with some good data that a 3.5 exhaust and a stock air box will flow enough to support up to 375-400hp. I am convinced the extra 1-1.5" in exhaust pipe would be irrelevant in my situation. Just asking and hoping someone else has ventured down the Power elbow or Brake road.(They both use the same exhaust pipes. One of the elbows just has a flap in it.)

 

Couple pictures of diamond eye 4” down pipe.



The collar is slip fit and welded into the down pipe, essentially 4” is bigger then the turbos outlet and choked down slightly to ~3.5”

Picture looking into the pipe. Not sure what gains would be had with a 4” down pipe on slightly modified vehicle but my money is on none.

 

If you are not set in the HPx, consider that removing the spring check valves from the HPOP side fittings will accomplish the same effect. I installed the Riffraff "high flow" HPOP fittings, new updated OEM hoses and new OEM head fittings several years ago.

New fittings and hoses can get expensive quick, especially if you start looking at the aftermarket kits.

Although, removing the HPOP fittings and the the spring check valves is free minus an o-ring or something that is worn. The fittings are fairly cheap at $15 or something if you wanted to go that route.

Essentially, you are not creating two additional HPO leak points, but allowing the oil pressure to "equalize" as the HPx does by removing the spring check valves.

 

I wasn’t clear. I’ve already purchased the HPX and installed it when I did the hydra about 2 years ago. It absolutely had a different idle. I wouldn’t say quieter but less cackle if that makes sense. It did make my ICP pressure more steady. Maybe it’s another smoke and mirror trick but I bit. I’m not dissatisfied and hopeful helped my injectors and HPOP. 🤷🏻‍♂️