wide open throttle??

[wally jr]

i'm in a disussion with my buddy who owns an imperial with a 305 and has never had his boat at wide open throttle. from reading posts in hear sometimes i hear "what is your wot"? is wot something you should know in order to figure out problems and or prop pitch changes??? and or just what good is it to know??

 

[JB]

Re: wide open throttle??

Yes, J.r.<br /><br />For optimizing prop selection you need to know WOT rpm and max operating rpm for the engine. On outboards you also use WOT figures to optimize rigging (trim and height, or, as DHadley calls it, the X dimension).

 

[wally jr]

Re: wide open throttle??

so theres no other reason to know WOT? if not thanks jb..

 

[James Bond]

Re: wide open throttle??

With a 305 wide open throttle will be acheived usually between 4600-4800 rpm's.<br /><br />If he has too short of a pitch prop, if he puts it at WOT and leaves it there, it will go cruising past his target RPM's.<br /><br />If he has too long of a pitch, he'll never get to his target RPM's.<br /><br />You'll just have to read around and experiment, there are tons of variables such as boat length, weight, hull design, engine condition....etc, so that it's not an exact science.<br /><br />It all depends on what he wants to do as well.<br />Using a shorter pitch prop will give you a better hole shot, but you may have to bring back the throttle on the top end so you don't over rev, therefore reducing your top end. For example, I use a 19" pitch on my 305 mercruiser, and on the top end I have to back off the throttle a bit to bring it into the desired RPM range, I am sacraficing speed by doing that, but I pull wakeboards and skiiers all the time, so I need the bottom end.<br /><br />Ok, I'm confusing myself now....im on too many drugs, blah!

 

[roscoe]

Re: wide open throttle??

Wide Open Throttle RPM's - WOT, Why its important to know.<br /><br />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 ("x" dimension), trim setting, 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 />If your WOT rpm have been in recommended range, but now they have dropped 500-1000 rpm, you know to look for the cause, before it causes further damage. Perhaps its an ignition failure, a carb problem, low compression, 500 lbs of water in the bilge, etc.<br /><br />Outboards run best 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, lowering performance, and decreasing the life of the engine. Not enough load, and you would 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.