Okay guys, please help me out if you can. I want to upgrade the crossover pipe and the rest of the exhaust on my truck the problem is, i want to keep the dual exhaust pipes coming out the side. The previous owner cut the cat and muffler out and put a splitter at the end of the pipe just under the bed and the two split pipes look like 2 1/4 inch pipes. Can I run 3 or 3 1/2 or 4 inch to the splitter considering that I have two 2 1/4 pipes and not lose any performance due to backpressure? Would the two 2 1/4 pipes cause any backpressure since there are two of them?? Thanks guys I appreciate any answers. And one other thing: where can I get the big exhaust kit other than banks? they have the whole package, and I already have most of the other stuff they have with the package other than the exhaust. :D

Area of dual 2.25" exhaust is 7.6 square inches, area of single 3" ehaust pipe is 7.07 square inches, area of a single 3.5" exhaust is 9.63 square inches, area of single 4" exhaust is 12.57 square inches. I wouldn't say your going to lose power to back pressure, but I do not think it would be a good idea to have a 3" downpipe into 4" muffler/tube then transition back down to the dual 2.25". Its always better to continually increase in size (on exhaust systems) not go from small to large then back to small. If you really want to keep the dual 2.25" your best flow would be 3" from the turbo to your existing dual exhaust. Watch out for the size of the Y where your 2.25" starts, if at any point it necks down that's where a performance hindering restriction will occur. Additionally if your 2.25" pipes are not mandrel bent all the area calculations are out the window, and I wouldn't recomend using them.

I bought my 4" system on Ebay $290 excellent system great hangers most mounted right to the factory hangers.