RPMs too low?

[Jeep Man]

I recently read a post about the need for a tach and it stated that if WOT rpms are too low it can damage the engine. How is this so and what is the difference between this and running less than WOT? My days of running full out all the time are in the past. I plan to be running at a speed far less than the engines capacity much of the time with the new boat. Is this going to be a problem down the road?

 

[Mike722]

Re: RPMs too low?

My understanding is that if the throttle is wide open but the engine RPM's are not at WOT range then the prop has too much pitch. The water resistence is forcing the engine to labor or slow down. This is hard on the engine.

Moving the throttle to a slower position is slowing the engine down by the throttle position, not by the resistence of the water on the prop.

The only problem I can see and maybe doesn't apply to marine engines is that most newer small engines only run right at WOT anything less will can lead to fouled spark plugs.

 

[64FAIRLANESC]

Re: RPMs too low?

If you are running to low a rpm at WOT you are loading the motor up just like trying to pull a backhoe at 55 mph with a Ford Ranger. You put a lot more stress on bearings and the drive train, ect. A dealer should be able to tell you what rpm you motor should run at WOT. If you give the prop pitch you have they should also be able to help you get the correct prop. Ask them if they will let you test different props to get the RPM's where they should be.

 

[Silvertip]

Re: RPMs too low?

Put it this way -- if the prop is wrong at wide open throttle, it is wrong at any rpm less than that. What that implies is that regardless what speed you choose, you need more throttle opening than necessary with a prop with too much pitch. A prop with too little pitch means the opposite in that the engine runs more freely but it is running higher rpm than necessary. If you have the right prop the engine will not labor excessively except at hole shot and it will not over rev or lug at wide open throttle.

 

[Jeep Man]

Re: RPMs too low?

Thanks guys. It's a bit clearer now.