So I have max boost of 30 pounds and max EGT of 1200 degrees. I have the stock exhaust straight piped. What effect on boost and EGT's will installing a 4 inch down pipe with either 4 inch or 5 inch stack have? Will it lower boost and will it cool the EGT's?

 

A larger exhaust should not lower boost psi. A larger exhaust will lower EGTs do to the more free flowing exhaust and less restriction,restriction create heat and heat raises EGT temp. I am running a 4in down pipe and 5in back and it sounds like a wind tunnel no restriction the differnt between a aftermarket and stocker is night and day, the weight,pipe size and bends all add up.

 

I did notice little cooler temps, maybe 50 to 75 degrees drop in temp. It spools slightly quicker, and after I pull in the driveway, the EGT temp drops a litle faster while in idle (I wait till it gets to 320 before I shut off).

Gotta be careful with the 4 inch near the heat exchanger under the turbo. There is a coolant hose that gets really close to the new exhaust pipe, as well as the frame a little further down. Can't imagine getting a 5 inch in there without some plumbing work.

You my need a second person just for positioning of that down pipe. It will clear both, but it has to be in just the right spot.

I did mine by myself, and it took a little time. I ended up breaking out the body hammer to gain a little clearance by the coolant hose. Did'nt need much, but did the trick. The tail pipe hanger had to be modded to work, but otherwise everything was a bolt up install. Kevin

 

i also found the in cab engine noise to be less,turbo spools a little quicker and about 100 less on the egt's, i have 4'' down pipe and 4'' all the way back.

 

I can believe the lower cab noise. My engine noise is lower with the larger turbo housing. The exhaust note is a little louder on pull, but the engine is quieter and smoother.

Looks like I need to get cookin and get the larger system on it. What I am planning is a four inch down pipe, to a four inch exhaust brake, to a five inch stack(s). Not sure yet if I am going with dual stacks at this time, I have a space problem with trailer swing. It will have no muffler or a fake muffler, in other words a small muffler with a straight pipe through it.

 

big turbine housings sound killer under moderate power... my truck HAMMERS below 2000rpm w/ about 1/2-3/4 throttle!!!!