Single 3" or 4"?
As to my earlier comment I run a 3 inch Y pipe with a 4 inch outlet and have the cut-out there. I have yet to run my present set-up on the dyno yet, but my previous motor picked up 2 and 3 mph (back to back to back runs) on the same day going from cut-out closed to open.
I would just do it the same size as the y pipe, but I guess 4" wouldnt hurt anything but ground clearance.


