4" vs 5".. is there really a difference. - Chevy and GMC Duramax Diesel Forum
07.5-2010 LMM Duramax Powertrain Discussion of components that are directly involved in the power production and all that is needed to get and keep the truck moving . Engine , Transmission Ect

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Old 11-25-2012, 08:06 PM   eBay Motors  #1 (permalink)
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4" vs 5".. is there really a difference.

Ok.. whats really the deal here. I have heard so many people I will like 5" better cuz it sounds awesome. Then i have alot of people telling me 4" is better and i will lose power with 5. Its almost about 50/50. What should i actually get? Id like 5 inch but not if there are downsides to it? I know i dont NEED it.. but i want it.
All im doing is EFI Live, straight pipe, lift pump, Blocking and rerouting, and transgo.

Pros and Cons GO!
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Old 11-25-2012, 08:26 PM   eBay Motors  #2 (permalink)
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There is no power loss associated with a 5 inch system as compared to a 4 inch
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Old 11-25-2012, 08:28 PM   eBay Motors  #3 (permalink)
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Thank you.
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EFI Live by Rob. Stock, Heavy Tow, Econ 90, Street 120, Race 150. S&B Intake. 5" MBRP Straight pipe.
3" mbrp downpipe. Blocked, Rerouted, Plugged. Transgo Jr. Edge Insight CTS. And no tread.

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Old 11-25-2012, 08:31 PM   eBay Motors  #4 (permalink)
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Quote:
Originally Posted by TrevorG View Post
There is no power loss associated with a 5 inch system as compared to a 4 inch
yep.

Sound is the only difference
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Old 11-26-2012, 07:58 AM   eBay Motors  #5 (permalink)
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Power wise, under 600hp there really isnt any difference between a 3.5" and a 5", maybe a little cooler EGT's.
Sound is the only real difference between them. The whole backpressure myth is still out there and a lot of guys think you need backpressure for an engine to run right. 2-strokes are about the only engine that "needs" backpressure, pretty much all 4-strokes can be tuned to run right without it. In a duramax the turbo is all the backpressure you need, anything behind it is there to get the smoke away from the cab.
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Old 01-02-2013, 10:40 PM   eBay Motors  #6 (permalink)
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Digging up a bit of an old thread here, but in my search for 4" vs 5" this popped up. As a response to the back pressure thing, it is not always true that lack of back pressure doesn't affect performance. I don't imagine it does for our trucks, but I had an 86 mustang with a 306 that was turbo (carbed), and when I went from a 3" down pipe and exhaust to a 4" down pipe and exhaust I lost nearly 10 lbs of boost. I know that isn't relevant with our trucks, but in case someone happens upon this thread and is working on an impractical project like my old drag car was, they won't be mis informed. Tuning a blow through carb set up isn't like plugging in efi live though.
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Old 01-02-2013, 11:05 PM   eBay Motors  #7 (permalink)
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Quote:
Originally Posted by jtyson8602 View Post
Digging up a bit of an old thread here, but in my search for 4" vs 5" this popped up. As a response to the back pressure thing, it is not always true that lack of back pressure doesn't affect performance. I don't imagine it does for our trucks, but I had an 86 mustang with a 306 that was turbo (carbed), and when I went from a 3" down pipe and exhaust to a 4" down pipe and exhaust I lost nearly 10 lbs of boost. I know that isn't relevant with our trucks, but in case someone happens upon this thread and is working on an impractical project like my old drag car was, they won't be mis informed. Tuning a blow through carb set up isn't like plugging in efi live though.
it also depends where the most restrictive part of the exhaust is. on our trucks its the turbo if you have a full system with aftermarket dp. with your mustang changing the downpipe could have freed up the exhaust a lot more causing the decrease in the speed of the gasses, which can result in boost loss. USUALLY having the freest exhaust possible after the turbo is a good thing, but our trucks make a ton of exhaust. compared to your mustang there is no guessing. I have also seen nearly a 25 hp gain from going from 1 5/16 to huge 1 3/4 headers on my 383 camaro which is n/a. every set up is different and for our trucks the different exhausts don't make any noticeable difference in performance only sound. The only thing if anything that could be lost is low end torque, which we don't use much of when racing or dynoing anyway.
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Old 01-03-2013, 08:21 AM   eBay Motors  #8 (permalink)
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Are you also going to do a down pipe? I have a 5" and love the sound, but I also did the down pipe and I am glad I did. The factory one has a pretty nice "kink" in it for lack of a better word!
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Old 01-03-2013, 08:33 AM   eBay Motors  #9 (permalink)
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factory LMM exhaust is 3.5"?

my LML exhaust (factory) looks huge, (thats what she said)

or maybe im just thinking it looks big, idk
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Old 01-03-2013, 08:37 AM   eBay Motors  #10 (permalink)
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To be honest I graduated college with a diesel degree and diesel do not need back pressure at all you can run them right out of the Turbo and you'll be fine all the exhaust is doing is getting the smoke out of there the bigger the exhaust the more.smoke it can move so the bigger the better and also you would have lower egts

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