I'm sure this has probably been covered somewhere before but I've got it on my mind. I currently have the factory exhaust straight piped, no muffler or cat. At some point when funds allow, I will be purchasing a 5" turbo back exhaust. I know that there's no performance difference in a 4" and 5" but I like the looks of the 5" better so that's what I'll get. Now here's my question, does a 4'' or 5" inch exhaust actually reduce pre-turbo EGT's over a factory straight piped exhaust? If so, how? I've got a pyrometer ordered and will be installing it this week. I've had pyrometers in 7.3 PSDs and 7.3 IDIs but I've never actually looked at the numbers on a factory exhaust because on those previous trucks, the first thing I've done is put an after market exhaust on them. I'm having a hard time wrapping my mind around how a bigger exhaust can reduce EGT's at the exhaust manifold, I always put the probe in the driver side exhaust manifold. Have any of you guys compared pre turbo EGT's between factory straight piped exhausts and bigger custom exhausts?

 

Pretty sure 4" is all that will fit from the turbo back and if its 5" to goes 4 to 5, not 5 all the way. Not sure on EGT's or performance gain on a stock truck though.

 

Had a hell of a time getting the 4" downpipe in, how can a 5" fit? Or is the system a 4" (or 3.5") expanding to 5" after the junction?

Josh

 

Yeah I'm pretty sure the 5" system has a 4" downpipe running into a 5" exhaust.

 

Not trying to steal this thread but just asked same question on excursion forum. Wondering if there is a difference in brands between performance and install. Is one easier to install than the other? I'll be watching this thread.

 

I've installed several MBRP down pipes and it was as expected. Installed one Diamond Eye and it was a b@$&h

Josh

 

I have diamond Eye on mine, duals did it on the driveway wasn't bad to do .......I've done worst on my back

 

I've installed 3 different diamond eye 4" on 7.3 trucks and they were a breeze. I don't think there would be a performance difference between brands. I'm just wondering if there is a performance difference between a 4 or 5" and a straight piped factory exhaust, particularly when it comes to EGT's.

 

Performance and EGTs are two different things in an exhaust set up. Performance wise almost everyone will argue 4" turbo back is all you need, and 4" DP to 5" is just for show.

I have a 4" DP to 5" diamond eye straight pipe set up and i had to beat and bend stuff to just that that 4" DP in you'll never get a 5" in there if you buy one.

For EGTs with a stock engine, i have never seen over 1000 ever, not even towing 8k. If you're going to be pulling 10k+ tuned you need all the pipe you can get i'd say, from what i read 1300 degrees before the turbo is danger

 

I'm pretty sure most if not all of the 5" systems have a 4" down pipe. My main question is will a 4 or 5" exhaust make a difference in pre turbo EGT's over a factory straight piped exhaust? I don't see how it can but I'm no expert.

 

Yes, 4" will make a difference, and 5" and even greater difference. The bigger the pipe, the more exhaust can be moved is less time than a factory system,

 

Actually too big of a pipe diameter can slow the exhaust down due to turbulence.

Can't say for sure a 5" will do that versus a 4".

Josh