can anybody out there help me with a small possibly stupid question? i want to run 5in. exhaust from the turbo back with 1 8in. stack. i ran 4in. from turbo back on my old truck with no cat or muffler and turned it out by the passenger door and a buddy of mine told me that my exhaust temps were so high after that because there was no back pressure is this the case or any recommendations on exhaust size

 

Couple things. Im fairly certain no one makes a 5 inch down pipe for the 6.0. A four inch will be TIGHT trying to get in there, but people do it (me). What kind of power are you looking to make. Most people are going to tell you to go with a 3.5 inch down pipe.
What were your exhaust temps? Its not backpressure, but the flow of the exhaust gas. Too large of a pipe will cause turbulance. To small is just a restriction. Either way, a 3.5 or 4 inch pipe with 4 or 5 inch exhaust will lower your egt's.
I'm running a 5 inch supertruck style exhaust, and I'm getting ready to either buy or build a downpipe. I'm going 4 inch, just because I know I'll keep trying to add more power.
I'm sure some one else will chime in.I'm not much of an exhaust guru. Good luck with what ever you do.

 

Your buddy has not a single clue as to what he's talking about.

No matter what exhaust you run, the turbocharger will give you any and all backpressure you'll ever need. That's why most states classify them as mufflers. You wont get a 5" downpipe in there anyways. 4" is real tight and they usually rub. A free-er flowing exhaust will LOWER your EGT's.

 

my egts on my old truck would get to 1650 and it never started untill i did the exhaust i asked around for a couple weeks and that is when a friend of mine told me it was a back pressure issue

 

It's possible you had some other issue going on, but a freer flowing exhaust isn't going to have MORE backpressure, it just doesn't make sense at all.

I've seen the EBP sensor do this (exhaust back pressure) though. You could also have a turbo issue, an exhaust leak, or any other of possible causes that could have done that, but a free flowing exhaust will lower EGT's. There is no question, it's a fact.

 

the biggest you can go is 4in off the turbo. mine only has maybe 1/8 gap from the fire wall