Best down pipe 3.5" or 4" for 7.3L ? - Diesel Truck Forum - TheDieselGarage.com
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post #1 of 11 (permalink) Old 10-29-2007, 11:40 AM Thread Starter
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Best down pipe 3.5" or 4" for 7.3L ?

I have a 3.5" dp to a 4" out the back ss t-409 magnaflow exhaust system , and I`m wanting to upgrade to a mbrp cool dual system in the t-304. Which is really the best down pipe to havethe 3.5" or the 4" ? Or does it really matter?

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post #2 of 11 (permalink) Old 10-29-2007, 12:38 PM
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If I was going to 4" cool duals I would just go 4" down pipe. Anytime you can go bigger on the down pipe the better.

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post #3 of 11 (permalink) Old 10-29-2007, 09:44 PM
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The problem with the 4" DP is fitment. It's a pain the azz to get it in there. As far as I know there is no power diff.

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post #4 of 11 (permalink) Old 10-29-2007, 10:24 PM
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i have a brand new 4" stainless steel downpipe forsale in the classifieds, i have one on my truck and love it, i went from stock to 3.5 to 4", so ive tried them all

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post #5 of 11 (permalink) Old 10-29-2007, 10:44 PM
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Quote:
Originally Posted by astro
I have a 3.5" dp to a 4" out the back ss t-409 magnaflow exhaust system , and I`m wanting to upgrade to a mbrp cool dual system in the t-304. Which is really the best down pipe to havethe 3.5" or the 4" ? Or does it really matter?
I would go with the 4" for better egt's. As far as fitment, it will go in just fine, you have work it in, but it is not that hard to put on:Thumbup:

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post #6 of 11 (permalink) Old 10-30-2007, 04:36 AM
 
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Go with the 4" dp, you will only have fitment problems if you had a 6.0 aka sick-o!!
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post #7 of 11 (permalink) Old 10-30-2007, 04:51 AM
 
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You will feel a bit of a loss in low end grunt more than likely, but the truck should move more freely at the top end. Given the mods you currently have listed, the 4" is really overkill and would more than likely be a waste of money. I'm making the power in my sig w/a 3.5" dp and no egt issues. .. of course, that's w/an H2E so it's a little different. If you gotta have it, it won't hurt. . .but i wouldn't expect to see too much from it.

-Brad Desatnik
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post #8 of 11 (permalink) Old 10-30-2007, 04:59 AM
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If I had 3.5" on it already I wouldn't bother buying a 4" unless I was planning on some big power. I really doubt you will see any difference with it. If you really just got to have it with your duals then go for it. Just don't expect any gains.

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post #9 of 11 (permalink) Old 10-30-2007, 05:27 AM
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Quote:
Originally Posted by astro
I have a 3.5" dp to a 4" out the back ss t-409 magnaflow exhaust system , and I`m wanting to upgrade to a mbrp cool dual system in the t-304. Which is really the best down pipe to havethe 3.5" or the 4" ? Or does it really matter?
I would suggest going with the 4" turbo back kit. The MBRP is a great kit, and as far as the fitment, you will be fine. The 4" will be better for future mods down the road as you begin adding more stuff.

Just my:2cents ,
Kenny
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post #10 of 11 (permalink) Old 10-31-2007, 12:20 AM
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the 3.5 was more for a stocker truck with air intake and chip and tuner the 4" is better.
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