cummins dsl

I know I probably won't need 5in exhaust, but at what horse power could I install it and it not hurt the performance of my motor. I'v been told they sound awsome on these trucks and I wouldn't mind being able to say that I have 5in exhaust on my truck.

Thanks.

Forrest Nearing

run it! it ain't gonna hurt

Forrest

BoostdCTD

I think the rule of thumb is 4" can support to about 450hp and 5" is anything above that, now where it hurts performance the most I don't know. The effect on performance shouldn't be very substantial but you may lose a tad bit if you are only running 300hp with a 5" exhaust. If it were me, I'd just do what I want and not really second guess it over the minute loss.

G1625S

yeah, what they said I'm settled on 5in, it's just a matter of 2 5in turn out stacks or one big sewer pipe out the back

Crimedog

I put 5" on mine and my first impression was it did hurt low end just a very tiny bit, but you're definitely pushing more fuel than I am. Would I go back, definitely no. I did make my own 5" downpipe (mistake), and I'm going to downsize to 4" on just the downpipe, because my theory is it is cooling the exhaust too much in the turbo before it can take advantage of it.

joefarmer

Technically, I don't think you'll benefit from 5" unless your turbo's exhaust housing has a 5" outlet flange on it. However, I ran a 3-5" reducer fitting right after the hx35 down pipe a month before the twins went on. I didn't see any noticeable decrease in power (300hp at the time). The biggest difference was the sound. It was a little deeper and much louder.

brandon.

mr T

u gonna run a 5 inch downpipe?? ...even if ur runnin 4 inch downpipe and then 5 inch the rest of the way id do it...for the sound and for future EGT reductions...u dont lose anything as far as im concerned...IMHO u wouldnt lose anything if u hacked the whole exhaust sysytem off and just had the junk come right out the turbo ... so go for it!!

KATOOM

I was under the impression a 5" down pipe wouldnt fit and a 4" barely fit. I cant say from experience but I have heard it does affect turbo spool if power is to low. Reason is with lower power levels the gases are to cool when expelled from the turbo and the exhaust is not hot enough to sustain the heat so the cool gases get cool to fast and slow while the hot gases coming in are running into the cool gases before they exit causing restriction. Someone just said you could run straight out of the turbo. Sure, because there is no gases to run into. But a hot exhaust pipe helps pull the exhaust along. This is why racers dont run straight out of the motors head without exhaust. Aside from the obvious engine damage, but more because their exhausts are tuned to the power level of the specific engine running. Exhaust is just as important as the rest of the engine for optimal power tuning. But I'm sure most of us just care if were setting off car alarms.

Forrest Nearing

4" downpipes fit great... plenty of room for a 5" downpipe, but I don't think a 5" downpipe will benefit any

Forrest

joefarmer

Five inch will fit. Here's a shot of the 5" downpipe under mine. It runs about 1/4" from the frame at the tightest place up towards the firewall.

durasmack

Is it best to run 4" downpipe with the 5" or is leaving the 3" on there better if only around 300 hp?

ds1rider

I'm contimplating getting the 5" straight pipe kit from Source Automotive. It comes with a 4" downpipe.

Forrest Nearing

4" downpipe is better than 3" even on a totally stock truck.

Forrest