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on my indy 488 fan i have her working real good other then the fact that i am working on trying to get my revs up .i like to get her up to around 7800 if im on the lake and pin her open she goes up to 8000 right nice for about 5 seconds then drops back down to 7000.what can i do ,or whats happening for this to happen.what do any body think this engine is good to go at relating to rpms is she capable of cosisting up to around 7800-8000 or is it to much
 

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Just out of curiosity, is there some reason that you want more RPM out of it? Typically, fans are rated at a considerably lower RPM than their liquid counterparts because of the drag from the fan and because the lack of cooling efficiency. The higher the RPMs go, the more heat is being produced and the air pushed through by the fan just can't remove that much heat that quickly. How exactly are you even getting it to rev that high? If you are thinking that you are gaining something by doing it, I doubt it. Two stroke engines have a narrow powerband. They are not like a car engine, which can make additional power by gaining RPM. The "powerband" of a two stroke is only +-200 to 500 rpm from the rated RPM given by the manufacturer. That is more than likely why your sled will not stay at 8000 rpm. Putting around under light load, it has no problem running at 8000+ rpm. However, as soon as the engine needs to work hard across the lake, it runs out of power and the engine rpm falls until it gains enough power to accelerate or maintain speed. The picture below is a guesstimate of what a two stroke powerband looks like. At 8000 rpm, you are probably somewhere at the right edge of the graph.
[attachment=56424]
 

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It helps to have your Tach Calibrated so you know what its showing is true. they can get out of wack just by use and abuse.
 

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i had an indy trail.. and it would do thae same thing.. be crossing a lake or a field and get it right wound out... then it would drop down to about 7000 too..dunno what.. buit it felt to me that the cluth was shifting , to bring them down.. but not 100% on that...
 

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the motor drops off power quickly above 7000. it's supposed to run around that rpm to be in peak power. turning more rpms will not make more power and even if you messed with the clutching to try and get higher rpms it might not hold simply from the lack of power up high. 8,000 would be way high for that motor.
 

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i agree^^
 

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My indy 500 liquid with my recent clutching runs 8000 with a good flat shift. I intend to drop it to 7800 and pour some more load on but thats besides the point.
Stock if you held it wot from a stop it would rev out to 8100 due to not enough shift, then it would level out to 7500 due to over shifting and too much load, then finally climb to 7800 and stay there. Stock single angle helixes suck for that very reason.
Proper clutching should yeild a "Flat Shift" or under wot from start to top end the rpms should be constant at peak power. At a reasonable cruise speed for your sled 45-60mph the rps should fall down or what some call overdrive untill you hammer it again raising rpms back to peak. 500s peak around 7800 or 7900 and many Clutch kits will set you in that range. A 550 fanner is a 7000rpm engine however and is a torque motor. It may be better for you to clutch yours in for 7600 or so being a fanner.
PAy attention to your tach and see what your sled tells you it needs. I would try a double angle helix. your early over rev means you need to load it more there (steeper helix angle) and your 7000 over load is just that so you would need a shallower helix angle. My guess is you have a 36deg helix. You might try droping in a helix near 40/32, or 42/34. $30 from EPI and easy to put on. Or buy a clutch kit but anyone can do that and have no idea why things do what they do. Any time you make a change Test IT AND RECORD IT!!!!!! Record your components and your sled performance So you know what the sled is telling you. Dont take what I say as gospal, I'm just trying to get you thinking.
Here is a good clutch info site. Try to read it all minus the first couple paragraphs and you will get an idea of how things should work. http://www.mxzx-revzone.com/iq.htm
Wow sorry for the long post.
 
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