Switched Propes - Want expert opinions

[Guest]

I recently bought a new 2002 Johnson and 17' Lowe V-hull. Motor came with a 14X17 aluminum prop. Wanted a more durable prop and found a good deal on a rebuilt 13X19 TSS. It gave me a couple more MPH at all RPM's which I was not interested in, but which is OK. Also dropped my top end RPM from 5500 to 5200. Is this OK? My boat dealer said it would not hurt motor. With old prop went 42 at 5500, now goes 46 at 5200. Overall everything well balanced, jumps out of hole and drives nice. Read on some other sites that recducing the top end RPM's might damage the motor but I wondered if a 300 RPM reduction was significant... i.e. if this loss of top RPM was damaging in any way, Thanks in advance - JLB

[Guest]

I've got a '99 Johnson 115hp. Stock aluminum was 14x17 and got 5800 RPM's at about 42 mph loaded boat. I borrowed a friend's "Raker" SS 13.25x20 and got up to 47mph at 5400 RPMs and it was way too much prop for the motor. Motor really hesitated at planing and vibrated a lot...too much stress on the motor, so not the right prop.
I then tried a 13.5x17 "SST" SS prop and got maximum performance! 46mph at 5800 RPMs and it performs perfect.
I talked to OMC and they told me that they want my 115 (V-4) at around 5800 RPMs for peak performance. You don't want to get the RPMs too much lower than that because it is too much stress on the engine (crankshaft, driveshaft, gears, etc.)

What engine do you have? RPMs vary with the engine. Do you have the V-4?

[Guest]

Motor is 90 HP 4 cyl, kind of forgot to mention that. I have not noticed any of the symptoms you mentioned.... sounds, feels and handles great. Owners manual does not include technical specs, and the OMC HSOforum location that gives specs for this motor has not been working last couple days. Just wondered if 300 RPM reduction was significant enough to be detrimental - JLB

[Guest]

I would say 5200 RPMs are a bit low (from what OMC told me on my 115), but look at the owners manual and see what the recommended RPMs should be. I think my engine is pretty close to the same as yours. You should feel if the engine is hesitating if the prop is not right. You might be ok if there is nothing unusual and don't beat the dump out of the motor

Another thing...are your speeds GPS speeds or the dash speedometer? My dash speedo told me 53 mph when GPS said 46 or so. Each prop gave a completely different reading on the dash speedometer! Something to consider.