Wide Open Throttle

[alexc]

You have the right combination - Fish & ski boat, properly tune motor & prop. On a calm day in the water, boat loaded with gears for a day of fun, how long/continous can you go "WOT". And why is "WOT" so important to others as I observe in the forum. What is the benefit of WOT?

 

[ob]

Re: Wide Open Throttle

If you have a properly tuned engine that is "broke in" you should be able to run at WOT for extended periods without problems.Actually ,I like backing off just a bit from capable WOT.The forum concern with WOT is primarily one of engine capability as it pertains to prop selection or other issues.Example: Each outboard engine has a manufacturer recommended WOT operating range.If for instance your engines was 5500-6000,then you would want to select a prop for your boat application that would allow your engine to attain a WOT range as such.Any more would cause engine to overrev and any less would cause the engine to be lugged.This can be monitored while operating boat equipped with a tachometer.Having one allows you to be apprised of how your engine is performing and can tip you off of problems before they go from bad to worse.

 

[roscoe]

Re: Wide Open Throttle

When running your engine at WOT, if it is reaching but not exceeding the recommended rpm range, the current set up is acceptable. By setup, I mean engine performance, prop, engine height, etc.<br /><br />WOT is used as a measure of how the whole package is working. If your engine is functioning properly, but not reaching recommended rpm, then something is putting too much stress or resistance on the engine. It could be a prop with too high a pitch.<br /><br />This is how you can zero in on the correct pitch prop to use.<br /><br />If your WOT rpm have been in recommended range, but now they have dropped 1000 rpm, you know to look somewhere other than the prop, perhaps an ignition failure, a carb problem, or 500 lbs of water in the bilge.<br /><br />2 stroke engines like to run at high rpm. You could run at WOT all day, or till you ran out of fuel and snacks. But best fuel enconomy is usually somewhere between 3000 and 4500 rpm.

 

[roscoe]

Re: Wide Open Throttle

Hey ob, guess you been speed typing, you beat me.

 

[ob]

Re: Wide Open Throttle

I think you said it better than I did.

 

[Link]

Re: Wide Open Throttle

Roscoe:<br />I recommended this site to a guy I have coffee with a couple times a week and he asked me the exact same question and I answered using the usuall WOT testing.. he then just says I don't care if everything isnt perfect.. So I then explained that unlike cars who drive on flat level roads and even get to coast and go down hill, that boats are ALWAYS going up hill with a load on the motor... Glad I'm not a teacher! But your explanation was perfect as to why he should care.. I just copied and pasted this into a email to him..<br /><br />WOT is used as a measure of how the whole package is working. <br /><br /> If your WOT rpm have been in recommended range, but now they have dropped 1000 rpm, you know to look somewhere other than the prop, perhaps an ignition failure, a carb problem, or 500 lbs of water in the bilge. <br /><br />Thanks as he MIGHT now want to care<br /><br />Link

 

[EsoxHunter]

Re: Wide Open Throttle

2 stroke engines like to run at high rpm. You could run at WOT all day, or till you ran out of fuel and snacks. But best fuel enconomy is usually somewhere between 3000 and 4500 rpm.

Does this mean 4 strokes do not like high rpm? I run my 2003 90 Merc 4 stroke WOT always (I like to go fast), I hope I am not doing the engine any harm, am I? Also what would be the best fuel economy rpm for this engine?

 

[Spidybot]

Re: Wide Open Throttle

Heh- that one had to come up...<br /><br />You may understand '2-strokes like to run at high rpm' as '2-strokes need a little higher rpm to perform' or '4-strokes have higher torque at a lower rpm'.<br /><br />There are fewer moving parts inside a 2-stroke and they often have a higher recommended WOT range.<br /><br />Having said that, recommended rpm at WOT is exactly that - 'recommended'. Provided your gear is up to it's best (tune, trim, prop & adjustments + sufficient warm-up before), you can run extended periods of WOT without worries. One should consider, however, the obvious difference in running conditions for internal parts at WOT and '75% WOT'. Goes for 2- and 4-strokes and btw. also has an effect on mpg.

 

[walleyehed]

Re: Wide Open Throttle

Esoxhunter, WOT doesn't mean the most power, but 4-strokes have a higher WOT range in some cases, and here's a small list;<br />Johnson/Suzuki-90.....4500-5500<br /><p> 115.....5000-6000<br /><p> 140.....5600-6200<br />MERC 50.....5500-6000<br /><p> 75.....4500-5000<br /><p> 90.....5000-6000<br /><p> 115.....5000-6000<br />When you look at the numbers, they don't seem alot diff. than 2 strokes but the highest torque is obtained close to the lower side of recommended WOT, where 2 strokes are rated generally the highest torque right in the middle of max recommended WOT-thats where the HP is rated on a 2 stroke. Hope this makes sinse to ya.........

 

[EsoxHunter]

Re: Wide Open Throttle

Thanks UU and walleyehed for explaining this to me. So if the most torque for my engine is at the lower end of the range, would I see better performance going to a different pitch prop? Right now I get 38 mph @ 5800 rpm.

 

[roscoe]

Re: Wide Open Throttle

Maybe I should have said that 2 strokes run better when the resistance or load on the engine is limited to the point, that recommended rpm's can still be achieved at WOT. Any more load than that would "lug" the engine. Any less load than that could over rev the engine. <br /><br />The engine operates best when the load matches the engine. Your setup is how you match the load to the engine. On a car, you have a transmission that does this.

 

[Spidybot]

Re: Wide Open Throttle

As your Max RPM (WOT) is 5000 - 6000 you're pretty close to perfect.<br /><br />You could consider an inch down in pitch (and get 6000) to achieve better hole shot. You'd most likely loose a little top speed. You also have room for raising the pitch by up to 4" which would reduce hole shot severely and result in 5000 rpm at wot. The relatively higher torque at lower rpm will help in this repect, though. Higher pitch would be useful especially if you do not care too much about accelleration and normally carry light loads. Would improve mpg when cruising at 'lowest possible throttle still at clean plane' (which, btw you state that you don't do as you like to go fast).<br /><br />You have a 'hole shot/top end' compromise in all cases. You can play safely with this as long as your max RPM (WOT) stays within 5000 - 6000.

 

[rubberduck85]

Re: Wide Open Throttle

I have a Mercury 150XR4 motor and I need to know what the stock propeller is. I have a 24" on it right now. It is cavitating very badly and i think it might be the propeller. Any help or suggestions with this would be greatly appreciated!

 

[Don S]

Re: Wide Open Throttle

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