I'm afraid the MC21 pipes will not fit, and frankly, trying to make them fit would be a mistake... possibly a very costly one.
The most obvious hurdle is the way the MC21 RHS pipe is routed to tuck under the Gull-Arm. The MC18 frame & bodywork is also noticeably narrower, hence why the MC18 pipes curl around at the front of the motor to make use of the available space. Fitting the chambers within the confines of the bodywork would be near impossible, I'd say personally.
Discounting the weight of the OEM pipes, they actually perform extremely well. Of course, many prefer the aesthetics of a race pipe, but [depending on use case scenario] in all honestly, the standard chambers are very difficult to beat. '89-'93 models will however, all benefit from aftermarket silencers. (1988 silencers are very unrestrictive, and you will see negligible gains by changing them.) The OEM chambers are capable of making power well past the mid 60s RWHP, and retain much more mid-range than a race pipe, but obviously lose out on peak RPM. As I say though, in the majority scenarios, i.e., street use, this is much less of a problem.
Aside from the immediately apparent physical differences between the chambers, it's the very small differences that can have the greatest effect on performance. While the basic engine layouts are almost identical, and many of the components very similar [and often interchangeable across many models], the 88~89 & 90~93 models differ quite significantly in their ignition and carburetion, and consequently the expansion chambers are optimised based on their specific requirements.
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Andy.
NSR-WORLD.COM
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