Exhaust size with H.O. set-up?

[84 Convert]

Hi everybody,
I'm trying to figure out if I really NEED to put a 4" exhaust on with my turbo+I/C set up. I will probably be running higher boost pressures, so I'm not sure if the 3" stuff I have currently will work out (I know the banks systems come w/3", but I'm quite sure I'll be putting out more than that) or if 4" is going to just be added expense for this penny-pincher.

In a nutshell I have most of what I need for 3" and will have to buy a complete 4" system if I go that route.

Come to think of it...isn't stock Dmax 3.5"? I'll be makin' less power than that!

Any help is appreciated.

Gregg

[TurboDiverArt]

Originally posted by 84 Convert:
Hi everybody,
I'm trying to figure out if I really NEED to put a 4" exhaust on with my turbo+I/C set up. I will probably be running higher boost pressures, so I'm not sure if the 3" stuff I have currently will work out (I know the banks systems come w/3", but I'm quite sure I'll be putting out more than that) or if 4" is going to just be added expense for this penny-pincher.

In a nutshell I have most of what I need for 3" and will have to buy a complete 4" system if I go that route.

Come to think of it...isn't stock Dmax 3.5"? I'll be makin' less power than that!

Any help is appreciated.

Gregg Having just gone through making my own, it's a fair amount of work. My strong suggestion is to just buy a 3.5" or 4.0" setup. That way you will be done in half a day vs. a few days.

As far as your performance needs. If you have a mainly stock setup, 3" mandrel bent tubes should be fine. Your stock main tube is 3". You need to cut out and replace with a piece of strait 3" tube about 6-12 inches beyond the DP. On mine there was a crush point where the 3" tube is crushed down to about 1.5", you need to remove this. Add in a new DP and muffler and you're adding on an additional $100-$125 to your project. You can get a 3

[gmctd]

Try the 3.5" system off a Ford Powerstroke crew cab - it's polish-grade stainless, incl the muffler, gives a nice mellow audio experience, and is cheap, usually free at those Ford upgrade get-togethers.

Worked out well on Grandpa's Big Truck, 5yrs now - try it, you'll like it.................

[ 10-10-2005, 12:47 PM: Message edited by: gmctd ]

[DA BIG ONE]

I'm seeing the muffler as an issue in 3" systems, I'm going to a straight pipe in place of free flow muffler to see, hear and feel the difference.

[Kennedy]

I've found 3" pipe to be too small for best performance gains, and 3.5" to be just right. For those wanting 4" I use a 4" tailpipe and transition 3.5-4" in the muffler. I believe that stepping the system this way produces the best results.

[84 Convert]

Thanks for the replies! I suppose I should have indicated that this is for my '84CC so, unfortunately, I can't buy a system ready-made.

gmctd, I'll have to go look at your pics yet again to see how you routed the exhaust...I'm having a hard time figuring out how to pass the downpipe and the crossover and still have any clearance. I've been considering a fender-dump style set-up and running outside the frame as I will be eliminating one side fuel tank and replacing it with a Suburban tank under the rear of the service body. The muffler could be stuffed up under the cab where the tank used to be.

I'll definitely be checking out the PSD system...

Thanks again

Gregg

[Kennedy]

3.5" still applies if you can get it and fit it.

[84 Convert]

Kennedy, your comments on size coupled with my being a cheapskate and gmctd's suggestion are all coming together here. Thanks for the great advice.

Gregg