i think the rule of thumb is a single pipe the same area as a pair of pipes will flow more. not really sure if this is true but i have read it more than one place. it is kind of like the x/h pipe thing only for the entire length of your exhaust.

i dont buy the too little back presure thing either. you will always make more power with open headers from at least 2000rpm up. maybe there is some loss under that rpm and that is where that info came from?

 

You get the advantage of reduced frictional losses with a single pipe vs. dual with the same flow area. There is less surface area on the inside of the pipe, and the velocity of the gas is less, so the Re # will be lower. But by the same token you can go too big and slow the gas down too much creating back pressure. Also a single pipe will probably weigh less. It's also hard to get two pipes to equal a large one. By that I mean, dual 3.5's still don't have the flow area of a single 5". Dual 2.5's don't equal a single 4", and they just have slightly more flow area than a single 3.5".

 

So we're saying go single pipe, but go big. Bigger then 3''. I might not be able to hook the FI up for a bit, would it be wise to go over 3'' without having it. Or should I do 3'' now, then modify to bigger pipe when I get the supercharger.

 

If it has to be single it sounds like 4'' would be a the size to go with as it will flow a lil more than dual 2.5s. So it it were me and I had to have single thats what I would do 4'' pipe.

 

Im sure you can run an aftermarket diesel exaust with little mods, maybe shortening a section if your a RCSB truck.

 

a single 4" on a 1/2 ton would be prety tuff to make fit. a single 3.5" fits prety good on my truck but it was close in some areas.

 

My single 3" rear of my turbo hurt my performance I will go 4" rear of the turbo one day.

 

Yeah, if you're running a front mount turbo, you won't get a 4" DP to fit without ditching the AC. And under the truck it gets real close around the transmission crossmember and where it goes under the crossmember in the back. For a rear turbo, a 4" tailpipe isn't and issue since it's already in the back. The big 4-5" diesel guys have 3/4 ton and 1 ton frames so theres a lot more room to work with. I've measured my truck (1/2 ton) and a 5" would fit once you're unde the truck, but I have the older crossmember style and it's super tight. 8ALTNG has 5" on his truck, maybe he can post some pics for us.