Well, the YS is designed for a tuned pipe. I tuned the Mac pipe on a test stand and the pinched off the end of the pipe. Got a brass pipe about 6" long and the same diameter as the end I pinched off, drilled a hole on an angle (towards the pinched off end) at the largest part of the pipe, inserted the brass about an inch and sealed the hole with a mixture of epoxy and carbon fiber chop. Now the outlet of the tuned pipe is facing the engine and exhaust goes through the prop (just like a byron pipe). Had NO loss in RPM with this mod to the pipe.
Todd