What is an acceptible range of RPM to be considered 'OK'? I'll try to use a tach next time I'm at the field. It definitely 'swung' the prop; I could feel the difference when tuning as the plane was pulling pretty hard, and it was climbing, and LOOPING, very well. There was just a serious drop in RPM, and again, tremendous fuel consumption and extra heat, unless I should be flying much slower with a bigger prop? I normally get 13000rpm at peak, then tune down to about 12,600 by richening the needle valve. And I normally fly at about 3/4 throttle, full throttle for climbs, with my usual 11x5 prop, but the plane flies A LOT faster. Maybe I don't need to fly as fast with the bigger prop.