Which pitch propeller you select will control the RPMs your motor runs. You need to select a pitch that will allow you to run within the recommended operating range for your motor (see owners manual). As you increase the pitch of your propeller, your maximum RPMs will decrease. And as you decrease the pitch of your propeller, your maximum RPMs will increase. For example, if your current propeller is a 19 pitch, and your motor has a recommended operating range of 5,000 - 5,800 RPMs at wide open throttle. But your current maximum operating RPMs is low, at just 5,000 RPMs. You may want to consider lowering the pitch of your propeller to a 17 pitch to increase your RPMs. A change from 19 pitch to a 17 pitch would increase your RPMs roughly 300-400 RPMs (varies by application). This would set your maximum RPMs to roughly 5,400 and you'd be running well within the recommended range. Blog: We have written a blog entry that further explains, in greater detail, how to select the pitch that you need. We suggest you take a minute to read that article, or call us for guidance.