If the prop is aluminum, 3 blade, it can be repitched at any prop shop lots cheaper than a new one, if ss they can be tweeked up or down 1 or 2. 17 to 19 sounds about right. at any rate your engine rpm should be aprox 5450 to 5500 maxed out and trimmed to be proped right, too high a pitch will cause the rev limiter to kick in, and to low a pitch is hard on the engine, poor performance, bad gas milage and poor handling. Hope this helps....Clay