Duke911, Do you want more power off the 'line' or do you want more speed? If you want more power off the line, then you need the 'single chamber' resonator. The dual chamber is for more power at the upper end of the RPM range. You may want to rethink the fitment of the parts you have selected. Looks to me the header and pipe combo is for the Traxxas PRO.15 and the header looks like it's for the PRO.15 also. I think the OS.18 has a round exhaust port, at least my OS.18TM has. My Jato has the OS.18TM, a Mugen Seki header, and the Traxxas 5485 Dual chamber resonator and it hauls butt. I hope this helps. Later, Bob