Wats the difference between using custom piping vs Off the shelf exhaust...does pipe material makes a huge diff?

 

As long as it's stainless steel it won't make too huge of a difference. The only thing would be weight, the thickness of the steel and the quality of the welds if the pipe diameter was the same. Also mandrel bends vs. crush.

 

I believe all aftermarket exhaust system are mandrel bent. Most muffler shop just do crush bent exhaust piping.