I flew OS 1.40RX the last 4 years. Very hard to beat the ES pipe, macs header setup. Very quiet. 86db at the NATS last year. Another great trick is to run K&B 1L plugs. I would get several hundred runs on a single plus with 15% Cool Power. I changed plugs the week before the NATS the last 2 years, just to say I changed plugs. My dad is still running the plug I took out last year in his sport plane. Very affordable too. That setup has great transition, great idle, nice top end 8100RPM on a 17X12. I left the header the full length with about a 1/4" gap between the header and pipe and just flew. Very low maintenance setup.

Arch Stafford