5in downpipe

[ShannonWilliams]

i don't see very many street legal trucks with 5in downpipes. i was wondering if their was a reason for this. i hear some say spool is slower and boost was harder to reach. true or false?

 

[CMChristensen]

i have a 5" DP an my truck is a daily driver..... mine spools great... .

 

[WCounts]

I don't know of anybody offering a 5" down pipe with the HX40 flange for the 3 gen. It would be a close fit with out any sharp bends and the ones that hook up to the cast elbow I wouldn't believe would offer any advantage over the 4". I believe by going to 5" just after the down pipe will be good enough. The turns in the exhaust is what causes restriction. That's why stacks are so good.

Billy

 

[SRadke]

If you aren't using a turbo designed for it there is no advantage. I have one on my S400 and is is a daily driven street truck.

-Scott

 

[Joseph Donnelly]

Clearance is tight for a 5” downpipe and production tolerances would make it difficult to mass produce such a downpipe. The bigger the turbine wheel and the outlet flange, the more the turbo is going to benefit from a 5” downpipe. On my 1997, I found that 5” helped once the engine was over 570 HP and that spoolup did not seem to be hurt at all. This effect makes sense, because once the gases have expended energy within the turbine and wheel, the faster they expand and get out of the way, the better. There is a lot of turbulence, sort of like what you see in a bathtub drain. The gases are also hottest as they come out of the turbo. These two situations mean that the biggest benefit from a 5” exhaust will be at the downpipe.

 

[WoodJ]

I got a 5" downpipe from source automotive that goes to the 4" cast elbo. It was easy to install and if anything it helped with spool up. I had a 5" flo pro cat back with the stock downpipe before. Hard to tell if it helped on EGT or performance, but no negitives that I can see.