Downpipe size

[mikem]

I am considering 3.5" vs 4" downpipe... i currently have a walker BTM in 3.5" sitting in its box. my current truck is almost all stock and was considering keeping it that way, but I have lots of parts laying around and have decided to get a few more and have a little fun

what I've got: stage 1 casserly injectors, TW 6 pos, 6637, beans sump, 205 tstat, gauges, racor pre-pump, buying an FRX

what I'm wondering is if there's any advantage to going 4" with the stock turbo? I got a brand new garret gtp38 a couple months ago when u was planning to just keep the truck all original (kicking myself now).

will a 4" downpipe give me any advantages over a 3.5" DP on 3.5" pipes and stock turbo in terms of EGT or spool, or just one less thing to buy if i upgrade turbo and exhaust?

is there any reason to go with a 4" full system with what I have, other than noise and fancy looks? my stock pipes are in good shape, and would add the aforementioned BTM muffler. could care less about its appearance, if i went 4" would run no tip

 

[ryanss22]

If you haven't already rip off your cat.. that helps spool up a lot.. not sure on a SD stock down pipe but an OBS is a squished rectangle.. so that severely limits flow. . But all in all, yes a bigger down pipe will help, more air out more air in...

 

[mikem]

If you haven't already rip off your cat.. that helps spool up a lot.. not sure on a SD stock down pipe but an OBS is a squished rectangle.. so that severely limits flow. . But all in all, yes a bigger down pipe will help, more air out more air in...

nice Cummins conversion, I'm jealous! i used to work for Cummins, machining and building motifs at the ReCon plant

fortunately my SD came with no cat

I'm definitely doing a bigger downpipe. just picked up a 3.5" magnaflow for a good deal, so i guess I'll give that a try since i already have a BTM and my stock exhaust is in good shape

What I was really wondering is if there's any EGT advantage to 4" over 3.5" once you get have done away with the stick restrictive muffler and downpipe. I know it won't provide any power advantage at the state of turn I'm looking at. no info to be found on that specifically, just 4" vs stock downpipe

i guess I'll find it soon enough if EGTs are an issue. I already have a 6.0 IC and will gut my EBP butterfly when I install the downpipe.

does anybody think wrapping downpipe is beneficial all, or just a waste of time and money?

 

[ghohouston]

4" downpipe shifts the power band up a bit

 

[pullandpray]

Wrapping is a waste of time. And 3.5 vs 4 is a waste of time unless your pushing 800hp then you might free up some. Still don't know if it would be worth it