Depends what you want. The MC18 in stock form feels a bit more like your traditional 2-stroke, with a strong pull once the RC Valves open, it also makes really healthy midrange. The MC21 is a much more flatter power curve and hence feels a lot smoother on the road.

The most powerful NSR's have been the MC21's though, once fully tuned. The most powerful MC21's though do use a lot of MC18 engineering.

It won't make a rat's ass to 99.9% of owners though. They all perform pretty much the same until you start throwing a lot of HRC parts at them. Even then, it's not just a case of bolting bits on, but also a lot of machine work.
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Andy.
NSR-WORLD.COM

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