4" exhaust- 3.5" or 4" downpipe? - Ford Powerstroke Diesel Forum
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Old 10-31-2011, 05:50 PM
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4" exhaust- 3.5" or 4" downpipe?

I'm getting a 4" turbo back exhaust and wanted to hear from some who already have them. Is there any rubbing on the firewall with the 4" downpipe and will I experience any power loss? My goal is to lower my EGT's and gain a little more power if possible. I've heard that some have experienced a low end power loss with 4" pipe. If it makes any difference I'm looking at the S&B intakes as well and the rest of my mods are in my sig. Thanks for the feedback.
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Old 10-31-2011, 08:25 PM
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I have 4 inch from the turbo back. I did not notice any power loss. I didnt notice a power increae though either. I would probably go with a 5 inch next time I did exhaust though that is for sure. I would do 5 inch with no tip just have that big 5 incher stick by the tire. I would actually love a single stack in the bed of my reg cab but who I am kidding. I also like my S&B cold air intake. No complaints whatsoever.
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Old 11-01-2011, 06:30 AM
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I have had both the 3.5 and 4" down pipes. I was running stock for a while between the two systems so I dont have a back to back comparison to give. I can tell you that other than bragging rights there is no need to fight a 4" pipe in a space where 3.5 works just as good.
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Old 11-01-2011, 07:19 AM
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Correct me if I'm wrong, but the stock downpipe is 3.5" - therefore, if you do not go any bigger than that, why bother getting exhuast at all? You'd just be wasting money essentially. Your exhaust system is only as "big" as your smallest link.

I have a 5" turbo back exhaust from MBRP, but my downpipe is 4". Therefore, my truck REALLY only has 4" of free flow. The exhaust opens up from 4" to 5" once it clears the firewall, and all that really does is change the tone of the exhaust.

Therefore, if you don't get a 4" downpipe - don't even buy exhaust. You won't get lower EGTs or more power from sticking with the same size downpipe, unless you shorten/straighten the exhaust flow.

That is how it's always been explained to me
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Old 11-01-2011, 07:44 AM
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An MBRP 4" turbo back w/cat was the first thing I did to my truck. The stock down pipe is actually 3 1/4" and the MBRP pipe was 3 1/2". I did just the cat back first and later did the down pipe, I really didn't see much differance in power or EGT's between the two, the truck just sounds a lot better without the stock muffler. What I found really lowers the EGT's is a custom tune 100 - 150 degrees lower min.
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Old 11-01-2011, 08:21 AM
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Ah, there you go. 3.25" downpipe instead of 3.5" - still pretty close and therefore not much difference. I doubt you'll see anything noticeable just getting the downpipe slightly larger. Either way, the exhaust will sound much better without the factory muffler.
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Old 11-01-2011, 01:56 PM
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Quote:
Originally Posted by fordfan30 View Post
I have had both the 3.5 and 4" down pipes. I was running stock for a while between the two systems so I dont have a back to back comparison to give. I can tell you that other than bragging rights there is no need to fight a 4" pipe in a space where 3.5 works just as good.
I agree, I stuck with the 3.5" after fighting a 4".
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Old 11-01-2011, 05:17 PM
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Quote:
Originally Posted by dhetrick2 View Post
What I found really lowers the EGT's is a custom tune 100 - 150 degrees lower min.
I'm already running custom tunes with muffler and cat delete on my stock system.

If a new exhaust system won't net me any cooler temps, I just don't want to waste the money when it could be invested somewhere else in the truck.

I think I'm going to try a S&B intake(but I won't be getting rid of my stocker either). I've done a lot of research and they seem to be good quality systems that flow better than stock. They won't hold near as much dirt before servicing as the stock filter, but my truck doesn't go offroad and its kept very clean. I'm hoping that if I keep the filter serviced and get some more air into the motor, I can get an EGT drop that way.

Don't really know what to do as far as exhaust. Vivian at Quick Tricks confirmed a slight drop in low end power with the 4" downpipe. I don't want to lose any power, but I also want it to run cooler....... Wheres a happy medium when you need one?
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Old 11-01-2011, 05:27 PM
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Quote:
Originally Posted by worldwide73 View Post
I agree, I stuck with the 3.5" after fighting a 4".
I thought you had the whole 4" system. Where you still seein' 1600* on the Looney Wild with your system? I also wonder if getting the EGR delete would lower the temps.

I just have to find a way to get these exhaust temps down or I'm gonna have to go back to a lower HP tune. If I drop the tune my mileage drops as well.

Maybe a different turbo is the only real answer. I've thought about a Batmowheel, but you have to change the outer housing and that costs another $125 on top of the batmowheel. Makes more sense to buy a new Powermax for around $1100, but that just isn't in the budget this year.
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Old 11-01-2011, 06:10 PM
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I was hitting 1600* with my SRL tune and stock exhaust with cat delete. After putting on my 4" straight pipe with 4" down pipe I can only hit 1400*. Can't speak for the 3.5" downpipe though.

I didn't notice any loss in power and didn't think the 4" downpipe was that hard to install. Just had to chop a stud off the firewall and it slipped right in.
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