Interactive exhaust valve

[The Spaceman_imp]

It's a valve that opens and closes depending on throttle opening. The idea is to increase back-pressure at lesser throttle settings and decrease it at higher settings. Generally speaking, it'll give you better performance at both settings. And by happy coincidence it keeps the bike quieter when you're putting along, and gives you more sound when you whack the throttle.

Yamaha calls it EXUP, and Suzuki has just added it to the new VStrom 1000 ABS; they call it "SET" which stands for "Suzuki Exhaust Tuning." The CB 1100 does not have the feature.