Must have missed it? Was there specific prop rpm data included, or were they relaying perceived/"butt dyno" results?
Regarding back pressure, I've had no issue with the Mac's pipe, the newer style Bison Pitts with small outlets, or the OEM. I really don't believe removing that center section is going to affect that at all. On the OEM, (as well as the Bison Pitts) I think tank pressure will be related to muffler outlet area - which would not be affected at all by removing the center section.
Last edited by ahicks; 12-12-2014 at 06:05 AM.