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3.5 OR 4 INCH DOWNPIPE

38K views 20 replies 13 participants last post by  mudoc 
#1 ·
I have heard that the 4 inch downpipe doesnt clear everything on the truck. What are your guys experience with this? Thanks
 
#2 ·
Mine seems to be fine. I have no rubbing issues, was just a really damn tight fit! Only issue with mine is, it will rattle loose every now and then. But that is just a clamp problem.
 
#3 ·
My 4in down pipe doesnt rub on anything.
 
#9 ·
factory downpipe on a 6.0 is already 3.5"

but

it's a spot where it's crimped or crushed down to 3" or just a tiny bit less. I've got the MBRP 3.5" sitting in my garage. looking up under there you can see a huge difference. I too heard about the 4" fitment issues, so I figured 3.5" was plenty. I'm not after a huge high HP truck. just slightly lower EGT's
 
#10 ·
Factory is 3 inch. I'm running a 3.5 inch fairly tight fit. Mine rattles since the day I put it in. There looks to be clearance everywhere but it rattles somewhere. Didn't notice any gain in throttle response or anything
 
#11 ·
Yea I very seriously doubt half an inch is gonna make a diff, if so I'd like to see some dyno numbers or somthin to prove otherwise, but hey it's whatever ur preference is I guess
 
#13 ·
you'd be surprised at the difference from the OEM pipe to just a 3.5" MBRP

I installed mine last night. Here they are back to back. Huge difference. I don't have calipers to measure the OEM...look at all the extra bends and crimps. that other pipe is the "test" pipe

 
#14 ·
Well mine has a 3.5 on it from when I put my exhaust on, I was just trying to figure out the 4 inch dp, whether it maybe lowers egts or anything beneficial Compared to just the 3.5
 
#16 ·
I have a 4" MBRP turbo back that is straight piped. I went to this from stock and noticed a jump in mid range throttle response most I would say. But I really like the sound over anything.

As for the fitment. I "modified" mine a little on install. I extended the downpipe a little and was able to rotate it to gain a little more clearance on the crossmembers etc.
 
#21 ·
Ive got 4" from turbo all the way out, Im running a straight through muffler and it sounds great. I do some trailer towing and I used to run one of my peterbilts with a straight pipe and the thought of listening to that roar all day and night didnt appeal to me any more. As far as clearance issuses, mine fit and it doesnt rub or rattle or come lose. one thing that I can tell you is when I did my install I had my bolts in my Turbo mount a little lose so it could move a little bit and once eveything was fitted and twisted and turned to fit I tightened it all down and its been good ever since! performance wise, I made several upgrades at once and I couldnt tell you it the 4"exhaust was a real factor by itself.
 
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