WOT= 4400 rpm

[brother chris]

Okay, I have a 16' fiberglass boat. I have a 1978 55hp Evinrude on it. At WOT, I am only at 4400rpm. I didn't have my GPS with me to check our speed. Oh yeah, the prop is a 15 pitch. Our guesstimated speed was approx. 35-40mph, probably closer to 35. <br />The boat gets up and goes quick. <br />Question is: should I be getting more rpm out of it. I was told I should be at 5300rpm when at WOT. If this is true, should I get a new prop(the one I have is aluminum, 15 pitch). Or should I just tilt the motor in different holes where the pin goes. I have done that on the first 3 holes(only 2 left to try), and again, max is 4400rpm. But it goes fast, like I said, 35mph.<br /> Next thing, how fast exactly does a 55hp go? I can't imagine it going much faster than what is goes now. But if it does, I won't argue.

 

[ob]

Re: WOT= 4400 rpm

I would check and validate tach is working properly.35mph with 15" prop at 4400 rpm sounds a little fast.

 

[tema]

Re: WOT= 4400 rpm

Running your motor with the wrong prop is like running your car in the wrong gear. You may go as fast as you otherwise would, but in low gear or low pitch prop, the engine runs too fast, in high gear or high pitch prop it works too hard. Either way, the life of the engine is shortened, in your case probably dramatically so. <br /><br />You should get a prop that gives you the recommended rpm's at WOT. If I were you I think I'd try a 12 inch prop first and see how it works.

 

[cmjust0]

Re: WOT= 4400 rpm

Sounds like it's overpropped a little... If you've got a good holeshot now, you should have a monster holeshot w/ a 12 pitch!! Each 1" of decreased pitch should gain you about 200RPM at WOT, so a 12" pitch should get you about 5000RPM. There probably won't be much (if any) difference in top speed, as you're going to a 'slower' prop, but turning it faster to compensate...

 

[brother chris]

Re: WOT= 4400 rpm

thanks guys, I will be taking the boat out this Sat. to get an accurate speed of the boat(with my GPS). Also, is there a way I can tell, or anything I can do to find out if the tach is working properly? <br />I appreciate all your help guys