Stupid Question from a Streetbike Guy

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#1
Okay, I know what a redlined 4stroke sounds like...but how do you keep from over-revving a 2-stroke? Does the power just drop off to nothing? I'm obviously brodcasting my ignorance here, but I've always wondered this. Surely the newer bike have revlimiters, right? What about older/aircooled ones? Thanks for indulging me.
 

CaptainObvious

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#3
You have to change your way of thinking.

There are two things that primarily determine the red line on a four stroke, piston speed and valve float. Two strokes don't turn nearly the rpm's of a four stroke and, we don't have valves, so a traditional red line that you are use to doesn't apply.

There is a practical red line for a two stroke however. When the ports do not have enough time to complete a combustion cycle you are at the power limit of the engine. The engine can exceed this limit in rpm, but power drops off dramatically. Some call this over rev. There is little to gain in this part of the powerband because of diminishing returns.
 

gwcrim

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#4
Redline (or optimum shift point) isn't necessarily something that you want to identify by sound alone. There's a seat of the pants feel when the engine power starts to drop off. By the time the valves are floating or the ports are overwhelmed you are WAY past the optimum shift point.

Might be a good idea to have an accelerometer installed in your butt!
 
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#5
I understand that, and have a good sense of mechanical empathy...but I guess what I'm wondering is...if you hold a 2-stroke open in neutral...does it just quit revving on its own for lack of efficency, or will it rev till it blows? Maybe I should try it on the neighbors bike.....
 

CaptainObvious

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#6
I see dudes hold the throttle at WOT all of the time, especially at the start of a race. I'm more of a "rever" myself. A two-stroke will rev until it simply can't rev any more and stay there.

I haven't tried holding the throttle open for an extended period of time, but if you can get a hold of your neighbors bike...