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alex92 said:
I'm guessing 1 rev = piston going up and down once? If so, is it the same on a 2 stroke?
Correct. One rev means one complete revolution of the crankshaft, which corresponds to the piston moving up the bore and then back down again (or vice versa if you start from TDC - that's Top Dead Centre, or the piston right at the top of it's stroke, as high as it can get).

One revolution is equal to two strokes. The piston going down from TDC to BDC (Bottom Dead Centre, or as low as it can get in the bore) is one stroke, likewise the piston going up from BDC to TDC is one stroke.

Two strokes are called that because each cylinder fires once every two strokes, that is, once every revolution.

Four strokes fire each cylinder once every four strokes, which equates to two revolutions. So each cylinder in a CBR is firing every two revs, which means two cylinders are firing per rev.
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