rubyred, I know you have a twin 1.60 but I figured I would offer this just as a point of comparison. I'm running a Saito 1.50 turning a Master Airscrew Classic 16X8 at 8800 RPM. I can loop my DPM Cub from "level flight" with authority at only 3/4 throttle, both tight and large loops! A wood Zinger 18x6 at 8200 should be yanking that Cub straight up and over the top with ease. If you're not, I suspect that you're either loosing power on the way up and/or maybe it has to do with your set-up. Did you balance the plane laterally? How much are you weighing?