I have a 1993 diesel with an aftermarket turbo on it. I had teh stock 3 inch pipe on it then opened it up to 5 inch. I have only seen gains in performance and in milage. I would reccomend this to you in a heart beat

 

2.25 is too small. well for mine it was. blown exhaust manifold. fixed. then blew apart the y pipe. then i tore the exhaust off past the y. a couple days later i decided to change the cab and haven't run it since and its comin out. don't go 2.25

 

I have a 7.3 IDI with no turbo. I was wondering if I can "straight pipe" my exhaust by simply removing the muffler and replacing it with a piece of pipe but i have seen the posts about the backpressure. If i do this will i retain enough backpressure so that i dont burn valves or anything?

 

i have a 92 7.3 idi non turbo with 2.5 true duals no mufflers, i have run these same pipes with glass packs(cherry bombs) and did not notice any difference either way, but gas motors thats a whole other story on the street

 

The backpressure myth is false. The valves are cooled by contact with the cylinder head.
People that burn valves after going straight pipes are also the same people that run their engines harder than normal, which is even worse on non-turbo engines because there is no boost to cool combustion. That extra heat is what burns the valves. A pyrometer is just as important to non-turbo diesels as it is to turbo ones!

 

What I've heard, and what makes sense to me, is that on a NA engine you need to size your exhaust propperly to maintain exhaust gas velocity. Too small, you get flow restriction, too large and the gasses cool off and slow down, and then they don't help scavenge the rest of the exhaust out of the cylinders. Once you get a few feet past the manifolds, the scavenger effect has done its job and you can go larger without harming anything. That seems to work in my experience, hope it helps

 

Sorry for picking up such an old thread, but you can place a turbo inline with the exhaust, which will still give you an equal amount of benefit, and will be easier to work on. AND it will more than reduce the scavenging effect that you are talking about. I've been thinking about doing this for a while now, just undecided on what turbo I want to use, and how I was to do it.

 

I have 2.5 right at the manifolds about four inches from the manifold it goes to 3" ... to the Y, then to 4" ... the big restriction is the intakes on these engines .. i run a 14X6" K&N filter ... picked up 2 mpg doing exhaist and air cleaner alone ... Royal purple 15/40 and Zmax ... another 2 mpg alone .... regurally was getting 17.5-18 city and 20 freeway .. they need to breathe .... if you ever pull the manifolds ... check out the size difference between the gasket and the head port ...LOL i ported mine .... wil have it done here soon