Since you are just starting out here are some suggestions. For a 40 size engine use a 10" prop with a pitch of 5 or 6. For a 46 engine go to an 11" with a pitch of 5 or 6. For a 61 size engine go to a 12" prop with a pitch of 5 or 6. For the 40 or 46 engines use a Master Airscrew brand. For the 61 engine use an APC brand. Don't go higher than a pitch of 6 in most cases. The extra pitch will load the engine down too much and you will actually lose speed. For all around good performance i like to use a 5 pitch[8D