Per the video indycars posted, the flow would be less than 500, so 2 1/2 inch pipe is what I would need! Depending on the location of the X pipe I will mount a support to the trans crossmember, then to the car in the area in front of the rear tires. I know with the shorter exhaust will be louder, that is the purpose of the X pipe, and to help with scavenging also!