89 Chevy Dually 6pack Exhuast with 12v cummins
 

I'm getting some pretty poor mileage and looked at my exhaust I believe it to be the stock 454ci exhuast and I'm trying to figure out what to run and where to get a setup. 4" or 5" muffler no muffler, who would have something like this or ???? I'm getting 10-13mpg and should be getting much better since my '95 got 22 empty. I want more power but yet need better mileage. Thanks

run a 5 inch turbo back exaust, that 454 exhaust is wayyyyyy to restrictive. no muffler

Ok so the down pipe is what size on these? I found out that I have a 3 3/4" exchaust with a muffler. If I go to a 5" I'm trying to figure out if I can just go to a local exhuast shop or if I need to order a kit but this is a hybrid so I'm guessing this will have to be custom made. Also any guess on the amount of power/mileage this will improve? Thanks

A 4" dp will be more than enough but the 5" makes it sound deeper. I'm thinking that since it is a custom rig you will have to get it custom bent and routed but that's also the cool thing cause it'll one off.

As for mileage improvements it should free it up a bit, not really sure if you've modded it and how much but you'll see a bit more response from the pedal.

I haven't done any modifications as of yet. I did go to a local shop and they want $1400.00 to do a new fuel system (I believe) and a couple of other things. I don't have that kind of cash right now but would be nice to have someone that knew what they were doing just to do it but I think since I own a place I can do the work I just need some guidance. I have been looking just haven't figured out where to start. I wish I knew exactly what he does for the $1400.00. He's gone this week.

Back to the exhaust. I do believe that my the system I have is very restrictive if I go with a 5" will that be from the turbo or should I do that from the cat-back? I am wondering the clearance issues. Thanks for the reply.

If clearance issues are present, a 3.5" downpipe isn't that bad. That way when you find the openings further down the line your can add the 4" or 5". There are plenty of guys here that have this swap and can probably help you out alot more than me, not very Chevy savvy.

Yeah I too would like to know what he does for, $1400 he'd better make a system that'll outlast the whole friggin motor.