Sizing your prop

[chumbucket]

"Loading" your engine within the recommended RPM range will also ultimately determine the life of the motor. Following the guidelines that Tin posted (excellent post BTW Tin), you're looking to obtain the Mfg suggested range. If you are below that range at WOT, you're working the motor too hard, burning excess gas, and poor performance. Above the range, and you're not working the motor correctly and will over-rev the motor. Not good.