What engine are you going to run it on? I have both the standard and big bore pipe. I have not run the big bore pipe yet as I do not have any of my bigger displacement engines done yet but hope to shortly. Matter of fact I need to call Mike owner of CPI tomorrow as he is suppose to have something ready for me. I talked to some at the Baja Challenge at Diggers Dungeon last weekend that like the standard pipe even on bigger engines better.
Here is a link talking about the CPI pipe.
http://www.rcuniverse.com/forum/m_8989168/tm.htm