Posts: 433
Location: Cedarburg, Wisconsin | Evinrude specs the 2007 and 2008 90 HP motors as 5000-5200 rpm for the sweet spot with 5500 max. You should prop the motor to run in the sweet spot for best economy and motor life. How you get there changes the performance.
If you want top end you have to have the motor as high as you can get it and still have water pressure. For the 90 HP you want a minimum of 19psi at 5000rpm and 20psi at 5500rpm. If you don't have a gage you'll never know for sure how high you can run the motor. Once you have the height right then you can work on stainless props to perform at that heigth to get rid of cavitation or blow out on hard turns. You might be giving away up to 3-5mph by running the motor too low.
Or you can just run the motor where it is and prop for 5000-5200 rpm and not worry about the top end. I'd try to run a cupped, vented, three blade 18" pitch stainless if it were my boat, and at least try to raise the motor, aiming for a combo that would let me get to the third hole if possible.
I know it's aggrivating trying different combos of heights and props and it would be so nice if were all spelled out for you but it isn't. It's just part of having a boat. All you can do is set it up the best you can. Not all hulls are the same, not all motors are the same, and not all boats are loaded the same so you can only get a general idea from similar rigs. |
