4" exhaust

im getting long tubes and a new exhaust and i was wondering if a single 4" will hurt my performance, if its just over kill so be it. i currently have a true dual 2.5" exhaust with a dual 3" in/out muffler. i plan on getting a 6L or bigger, cam, and who knows what in the future, i got my current exhaust and headers before i supercharged the truck and its time for a change. i dont think i would gain anything from a single 3", i would go for a dual 3" set up but i can get a single 4" for next to nothing, all the diesel guys around where i live all have stacks and their are lightly used 4" exhausts that can bought cheap . any one an exhaust expert? i would rather get my idea shot down before dropping money on an exhaust that will hurt me.
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I suggest sticking with 3". I know from experience that it is super difficult to find anyone who can bend 3.5" pipe... much less 4". At the most, dual 3".

if you went with a diesel exhaust you prolly could cut up and fab something up pretty cheap i replaced exhaust on my 01 dodge with a 4in off an 04 and it was a direct swap basically but the easiest way you could could possibly make it work is with a dmax exhaust and i think they come with 3.5" anyways

Imma agree. I am going dual 3in because I couldn't find anyplace around able to bend 4

I bought a prebent 4" exhaust from SummitRacing, it's a diesel truck exhaust.

i found a nib 4" stainless duramax exhaust with a muffler and 5" tip for $250 shipped to my door, so will it hurt or help my hp?, that is my only concern, i like the overkill part of it. im getting the speed_daddy ebay lt's right now and the 4" exhaust has a 3" to 4" adapter so all i would have to do is weld a flange to the adapter and do a little trimming on the length and i think i will be good, so no exhaust shop or bending will be involved, all the hangers and t bolt clamps are included.

I dont think it would make much of a difference. I think the average size of most just bolt on trucks is probably about 3" single or duals and since your boosted it probably wouldnt hurt to go 4". As long as your geared right and have a nice stall you shouldnt lose anymore bottom end I wouldnt think.

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Originally Posted by st8kfinger

i found a nib 4" stainless duramax exhaust with a muffler and 5" tip for $250 shipped to my door, so will it hurt or help my hp?, that is my only concern, i like the overkill part of it. im getting the speed_daddy ebay lt's right now and the 4" exhaust has a 3" to 4" adapter so all i would have to do is weld a flange to the adapter and do a little trimming on the length and i think i will be good, so no exhaust shop or bending will be involved, all the hangers and t bolt clamps are included.

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As far as I know the speed daddy headers are 2.5" collector...if you don't have LT's currently I would save up and get good headers...like kooks or stainless works. Just my .02

I have a duramax exhaust on my 2005... i have the stock true 4" rear section from a NNBS GMT900 2500 4x4 duramax truck.. i believe its an 09. Then i have a 4" CAT delete pipe for a GMT800 2500 duramax truck.... and that went up far enough to hook in to my 5" downpipe right next the transmission. The GMT900 rear muffler and tail section was FREE and fits in the GMT800 1500 exhaust hangers PERFECTLY. Then the GMT800 cat delete pipe is for a 2500 crew cab and it has the proper bends for a GMT800 1500 ext cab chassis... So i have a $75 4" exhaust... and the big factory 4" muffler sounds pretty sweet.. its extremely low restriction and you can easily hear the turbo spool. I will try to get a picture up so you can see what it looks like.

Edit...
The GMT900 2500 cat delete pipe does not fit the 03-07 NBS 1500 ext cab chassis... the bends are in the wrong place and the hanger is moved. The GMT800 duramax exhaust will fit, but its not a true 4" like the NNBS trucks.

I dont believe a 4inch single will gain much, if any, but it certainly will not hurt anything.

If you look at the chart above, you have less sq inch in the cross section by having a single 4" then you do with the true dual. 2X7.1=14.2 sq in with the 3" vs 12.6 sq in for the 4". Seems pretty straight forward to me (from an exhaust out sort of point of view that is). I'd say unless you "just want it", I'd stick with the 3" dual setup you have now.

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Originally Posted by bangbangskeetskeet

As far as I know the speed daddy headers are 2.5" collector...if you don't have LT's currently I would save up and get good headers...like kooks or stainless works. Just my .02

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the headers are a 2.5" collector, but the y-pipe is a dual 2.5" into 3". it bolts right up to the factory pipe

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Originally Posted by zebra

the headers are a 2.5" collector, but the y-pipe is a dual 2.5" into 3". it bolts right up to the factory pipe

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That's all fine and dandy, but an exhaust is only as efficient as it's smallest point. Just like an intake manifold...that would be like having a 102mm intake with a 78mm throttle body. It's pointless to do the upgrade cause you can only flow as much as the smallest point. Hence why I suggested something with a larger collector, such as kooks or stainless works. I am 90% positive you can get a 4" collector with kooks, but not sure about SW.

Edit: I just looked on the kooks site, and they only offer 3.5" collectors, but I thought someone had said they will do custom orders?

thanks all, i got a 4" polished 304 stainless volant exhaust with 6" tip and ebay lt's for $425 and change shipped(for both), if i dont like it or it sucks i wont loose any $

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Originally Posted by st8kfinger

thanks all, i got a 4" polished 304 stainless volant exhaust with 6" tip and ebay lt's for $425 and change shipped(for both), if i dont like it or it sucks i wont loose any $

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Thats a killer deal man! Hope to hear some clips of it after its done! :thumb:

i got two 4" volant exhaust's, the $'s i posted is for the lt's and 1 exhaust, for the price i got i bought 2 exhaust's. im getting ready to buy 2 more exhausts, not to gloat but im making a killing off of them, as long as i can flip them i will keep getting them. will do, im getting antsy to hear it myself, just got to call nelson's for a retune and i got a digital camcorder today so i will get a clip up about 5 min after its done.

Sweet!