Dumb question of the year: W.O.T. question...

[DrD]

I have a 1991 Mercruiser 5.0LX TB with Alpha one Gen II. The placard on the engine says the maximum WOT is 4200 to 4600 RPM.

I am wondering what that means? Is this a do not exceed RPM, or is the engine designed to run at that RPM under normal(?) operation? If that range is achievable, I guess it says a lot about the drive system overall, but I wouldn't want to damage things by messing around and running it at that RPM.

I'm pretty new to this stuff, so I'm just trying to get a good understanding of the overall operation of things.

Thank you,

-Dale-

 

[Haut Medoc]

Re: Dumb question of the year: W.O.T. question...

With the throttle wide open & the proper prop, under normal conditions, the closer to 4600 the better.......
If you exceed that you are propped wrong....
If you can't get to 4200, you are propped wrong or have other issues......
Lugging the engine is bad......
It would not be wise to operate the engine above 4600 rpms for any extended periods of time.....​

 

[wire2]

Re: Dumb question of the year: W.O.T. question...

I'll add another dumb question, what happens if you exceed 4600 rpm for extended periods? Modern car engines typically are fine up to 6000 rpm, (although rarely sustained), so I'll guess that 4600+ creates issues with outdrive mechanicals?

 

[MikDee]

Re: Dumb question of the year: W.O.T. question...

I'll add another dumb question, what happens if you exceed 4600 rpm for extended periods? Modern car engines typically are fine up to 6000 rpm, (although rarely sustained), so I'll guess that 4600+ creates issues with outdrive mechanicals?

Not necessarily, the drives are fine within reason, and some are designed for high HP motors, but boat engines don't ever get to coast, so they are always under a load, by keeping the revs down they can last as long as your car engine, or they'd burn out sooner. Even if you have a highest hp motor, you gear it down with the prop, to keep it in the 4200-4600rpm range. 4600rpm with the lightest load, to 4200rpm with the heaviest load, it is better to Err a bit towards the higher end of this rpm range, rather then lug the engine.