Prop diameter diiference on a 1989 Evinrude V-4 SPL model E88MSLCER

[B.autry4711A]

Hello Guys,<br /><br />I have a question on a prop. Will the diameter on a 12 3/4 X 21 and a 14 X 19 change the RPM's. What I am asking is will going from 14 X 19 prop that is turning 5000 RPM's go up when I change the prop to a 12 3/4 X 21 prop since the diameter of the prop is smaller or will it balance out or loose RPM's? I ask Because I installed a new used tachometer this year and have had the boat out once and haven't checked the 12 3/4 X 21 prop that originally came with the boat and it was reconditioned. I just wonder if that 12 3/4 X 21 prop which was onthe boat when I bought it 2 years ago cause my RPM to go up since the diameter is smaller in size. The anticavittaion plateis 1 inch (approximately) above the bottom of the keel on the transom.

 

[walleyehed]

Re: Prop diameter diiference on a 1989 Evinrude V-4 SPL model E88MSLCER

Diameter is a big part of the total design of the prop. OMC alum. used to be 12-3/4X21, 13X19, 13-1/4X17, 13-3/4X15..That line of props has simular blade designs...then, they came out with a long-eared blade design, and stayed pretty much at 14" diameter for all of them.<br />The 12-3/4X21 has never been a super performer unless installed on a very light boat. <br />Now, you're talking about 2 different blade styles in the props you list, and I'll bet the 14X19 is the best of both.