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Turbo downpipe - 3.5" or 4"

11K views 11 replies 11 participants last post by  Vdryv 
#1 ·
I'm getting ready to buy a turbo-back exhaust for my 2002 F350 with 6 speed manual trans. I've been reading that a 4" downpipe will loose some bottom end torque and that for an everyday driver vehicle, a system with a 3.5" downpipe would be better. Any thoughts or experiences ?
 
#2 · (Edited)
I have an MBRP 4" turbo back straight pipe on my 99 7.3 auto 4x4 ex cab lb. I noticed no low end power loss with it. Sounds real mean and definately brought out the turbo whistle.I'm very happy with it.
Kit was very easy to put on, hardest part was to get the band clamp off the turbo. I would suggest soaking it regularly before trying it, I ended up having to deform it with a flathead to get it off, but it bent back no problem and doesn't leak at all.

I cut the old exhaust in two places, at the bottom of the down pipe, and right after the cat. (I cut it after the cat as a band aid, because I backed into a snow pile and deformed the back half of my exhaust, so that cut was just already there.) If you are doing it in a driveway, I'd also suggest cutting right after the muffler, as it is a ***** to get from the cat back over the rear axel, but it can be done because I did it all by myself. I had no space in at the time either.

On a side note, a 4" downpipe fits in the space perfectly, but any larger of a pipe would be a bear to get in there. The rest of the run wouldn't matter as it is so open.
 
#4 ·
I have a 4" on mine. i have not noticed any loss of low end torque. i know my E99 does whistle pretty good with this downpipe. I even have 6.0 guys compliment me on my whistle.
 
#6 ·
no performance difference between the 3.5 and 4" dp on stock set up. I have heard the 4" does not fit the e99 6 speed very well. You will not know the difference between a 4" and a 3.5" though
 
#8 ·
I guess I'm to old for this stuff, but I learned years ago that no one part makes it on every rig. Box stock the 31/2 would probably work fine. When you start turning things up you might want to have the 4"". Its hard to do but if you can look ahead and see where you want to go, then match the parts up for the end result. With my chip turned off I can't even get out of the driveway.
 
#9 ·
I guess I'm to old for this stuff, but I learned years ago that no one part makes it on every rig. Box stock the 31/2 would probably work fine. When you start turning things up you might want to have the 4"". Its hard to do but if you can look ahead and see where you want to go, then match the parts up for the end result. With my chip turned off I can't even get out of the driveway.


LOL...

To the OP... 4" turbo back will fit fine, and will give you no loss in power.
 
#11 ·
I have used both 3.5 and 4" down pipe (magnaflow, MPRP)...currently running the 3.5 with both mufflers inline (MBRP, magnaflow) 3.5 down - 4" all else.

On the 6.0 the 3.5 was said to spool better due to the design..on the basic turbo design of the 7.3 - no difference.

I have a drone issue I have been chasing for years, that's why the different systems. I also have a areoturbine muffler that makes things worse (noise wise) when put into the mix. EGT's are all too close to tell towing heavy, uphill, and fast (PHP tunes).
 
#12 ·
Found that after I cut stock down pipe to get out and tried to install mbrp 4" didn't want to fit with 6 speed so I will install it when it's at the tranny shop for warranty. My drips everywhere like she's on her period lol
 
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