2 stroke question...

[Screamin440]

Since a 2 stroke has no valvetrain do they have an rpm limit? What I'm wondering is can they just keep revving like a rotary engine can? A rotary engine really has a limitless rpm range since they have no rotating mass and no valvetrain.

[Toadz400]

I believe they don't have a limit, just as fast as the piston and crankshaft can move, unless there is an eletrical device that acts as a rev limiter...but I haven't heard of those on 2-strokes? Sooner or later it's going to blow though...

[mojoe2878]

my 2 stroke dirt bikes rev out at around 10,500 rpm where as my 4 stroke yzf's rev out at over 13,500, a two stroke does have a rpm limit as far as what it can take with out grenading on you.

[bradley300]

yhe way i understand it is you can build a two stroke to rev as high as you want, but how high it revs depends on porting, size of the motor, pipe, yadda yadda yadda. a two stroke will not rev forever for the sheerfact its a two stroke but you can build them to rev to limiltless rpms. make sense?

[wilkin250r]

Yes, two-strokes have rev limiters built in to the CDI. The rev limit of an engine has several factors to it, not all of them are the valve train.

Newton's Second Law says Force equals Mass times Acceleration. Really, it actually means Force equals Mass times the change in velocity. The piston is moving in one direction, and then switches and goes the opposite direction. This represents a pretty drastic change in velocity, doesn't it.

So basically, that force and change in velocity takes energy, the faster it goes, the more energy it requires. This means that at very high RPMs the power output of the engine starts to drop off. It also means that the faster the engine is revving, the more force is exerted on the connecting rod. Eventually, the connecting rod will break. This would be the "natural" rev limit of the engine.

Your CDI has a built-in rev limiter. This cuts the spark beyond a certain rev limit BEFORE damage occurs in your motor. This is obviously to protect your motor from destruction.

[speedkills]

my first race ever was on an stock motor blaster i mean stock no pipe nothing. i couldent hear my motor over any of the other motors, this is bad and dont try it but i would just rev the thing to i felt the limiter hit in and i would lose speed, kind of like boging down. so yes 2 strokes do have rev limiters.

[Scott-300ex]

they couldn't just rev forever, use your weedeater and you'll find out, the motor can only go as fast as how much gas the carb can put out.