93 7.3 idi exhaust question
 

hey to everyone out there, i'm new to the diesel world and was wondering about an exhaust upgrade for my 1993 f-350 7.3. i have read many threads and articles saying not to go bigger than a 3 inch exhaust on a non turbo because the muffler and smaller pipe causes back pressure that is needed. but on a turbo it is ok to go big because the turbo causes the appropriate back pressure needed. so i would like to know is this true or is this all just a folk lure. i would really like to stack my truck. thanks for any and all help.

That is true on the IDI's. I have ran 3" to 5" stacks on them and been fine on a non turbo'd IDI. We used a y pipe as well. I have had friends that had 4" and bigger on them and they have had valve train problems sooner or later with them. Basically burning valves.

:welcome: to DB..

I dont buy the whole backpressure theory as I never run mufflers on anything and have never had any problems or lost any power doing it. On my IDI I run a 3" down pipe into a 4" straight pipe that splits in the bed into 5" stacks. Anything bigger than 3" really isn't going to help anything but the sound quality though. For the N/A trucks, most guys run 2.25" or 2.5" duals or will run them into a single 3" pipe.

Sycostang; you have a turbo so that gives you the needed back pressure, with out one you do need something for back pressure. I tried just the y-pipe and about a foot of the intermediat pipe before my turbo was incstalled, loss of power and about 50 miles later it would fill a 5 lane road with blue smoke going 35mph... So in conclusion you do need some back pressure, a 2.5 inch cherry bomb seems to be enough though. my 7.3 had one and my cousins 6.9 still has one. Also watched as we burned out the valves on a Hough model 120 front end loader from lack of back pressure, so yes some is needed.

Hey everyone, thank you for the information on my question so i will probably stick with the back pressure and go to the 2.5" dual setup but i want to run a few more tanks of fuel through her to get a good base line for my mileage and power. right now with a dirty air filter and synthetic oil no other mods have been made and i am averaging just over 20 mpg:rocking:also thanks for the welcome aboard, i am sure i will have plenty of more questions in the future but for now i just want to start out kind of simple with the upgrades. once again thank you all.:c:

Maybe it's different for the N/A diesel motors, but I've never had issues with a gas motor. My last truck had a 460 with straight 2.5" true duals into 5" stacks and my mustang has long tubes with an X-pipe and straight 2.5" exhaust as well. I'll be picking up an 86 N/A 6.9 shortly, maybe I'll tinker just to satisfy my own curiosity. :humm:

It's something that diesels need, try running a gasser with open heads (no headers) and you will notice a little loss in low end tourque, all our engines have is low end torque. Or you could take that snail shell shaped restriction out of your exhaust and give it to me :w2: so that you can experiment with your 7.3. lol

That had crossed my mind because I miss the sound of my 460, but I think I would rather have the extra power from the turbo. :tu:

Trust me, you would.

exhaust myth
 

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:c:

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