4" or 3.5" down pipe?? - Ford Powerstroke Diesel Forum
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Old 04-30-2012, 10:19 PM
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4" or 3.5" down pipe??

I'm upgrading a few things on my truck I just bought its bone stock right now. 2003 7.3 F-250 AT Crew Cab Long bed Lariat 4X4 97,000miles plans are Autometer Gauges on Pillar (being shipped now), AFE Stage 2 Intake, 5" Exhaust, and finally TS 6 Position Programmer for now. When parts start to fail they will get upgraded then like injectors, turbo, fuel pump, ect. My question is has anyone notice any power loss in the low RPM's when running a 4" down pipe vs. The 3.5"?? I found a few 4" down pipe to 5" strait systems and I love to tone of a strait 5" but I have heard this from a small hand full of people that the 4" made them lose bottom end power but wasn't sure if its something I should take into consideration or just someone who screwed up somewhere and don't have a clue about diesels?? I'm new to owning a Diesel but have spent my entire life around them and just trying to build this one the way I want it but with the best outcome possible.

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Old 05-01-2012, 01:16 AM
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You're going to get the same response people receive when asking if a 5" exhaust is too big. Do you need the low end? Do you need it so much that you'll notice and dislike the loss? Most peoples answer will be no... In that case do what you want, go for the sound you want... But that's my opinion

On another note 4" will fit but is tight.. I personally see no reason to go with a 4" over a 3.5". I've seen big hp with 3.5" DP.. Then there's the other side of the coin that says the more movement you have the better (and lower EGT's), etc
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Old 05-01-2012, 12:40 PM
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go 4 inch my egts went down 400 degress spools a little better (ITS A GOOD IDEA)
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Old 05-02-2012, 12:12 PM
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there is no difference between a 4" and 5" in performance. Only sound. The outlet of the turbo is 4" so once you hit 4" the choke point becomes you turbo, not your downpipe. But at least get 4" downpipe or else you are restricting your truck after the turbo. I gained low end tourqe and dropped egts with the 4". Its hard to notice empty but when pulling heavy loads it makes a huge difference.

My 4" system from MBRP lined up great. didnt have any issues with the dp fitting. I have intsalled two and both were very easy to do.

Last edited by jacobm24; 05-02-2012 at 12:16 PM.
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Old 05-04-2012, 04:31 AM
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Thanks for the info guys! I'll keep ya posted on the upgrades as they come. My pillar pod just came in now to order the gauges and buy a cheap on to gut to use as a mount for my 6 position switch. Then the AFE stage 2 and exhaust will go on and the tuner will get installed after those are on. My plans are to leave it at that and then upgrade other things start to fail.
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Old 05-04-2012, 09:42 AM
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4" Definitely! Mine fit with room to spare.
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Old 05-04-2012, 10:02 AM
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Yea, kind of a "no-brainer"
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Old 05-04-2012, 10:24 AM
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Quote:
Originally Posted by ff_cspires View Post
Thanks for the info guys! I'll keep ya posted on the upgrades as they come. My pillar pod just came in now to order the gauges and buy a cheap on to gut to use as a mount for my 6 position switch. Then the AFE stage 2 and exhaust will go on and the tuner will get installed after those are on. My plans are to leave it at that and then upgrade other things start to fail.
I mounted mine on the panel to the left of my little cubby hole thing, and my brother did his next to his 4wd switch. It is easy, looks clean and is easy to reach. Plus it is free if you have a drill and bit.

The gauge thing is a good idea but it costs money and it seems like it would be more out of the way (in a sense) when you want to switch tunes. Just my opinion/input though!
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Old 05-04-2012, 11:00 AM
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4" most definitely man, get those egt's down and fits fine, 2 man job though is best, 1 holding it from underneath while man up top bolts her up.
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Old 05-04-2012, 11:01 AM
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yeah, 6 pos chip, the removable panel right at your left knee, just drill her, you can reach and still have a eye on the road, thats where mine is and the east tx boys installed it, they said thats where most all their installs go.
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3.5" down pipe, 4" down pipe, 5" exhaust, performace parts, upgrades

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