I've got an 61 fx in a fresh built Killer Kaos with tail dragger retracts @7lbs. I'm running a 12x6 MA with the stock muffler baffle removed. I know different engine but am curious what rpms you guys are getting on the ax with the prop sizes and exhaust set ups? I'm thinking of putting a tuned pipe or maybe a Jett type muffler, and trying different props to get a little more performance.