Yoshimura RS-4 Race Series Full Exhaust System

Forward of the muffler, the exhausts are mostly the same. It's the mufflers themselves that differ between the two with the RS-12 being the latest iteration of their offroad-focused muffler design. Being the '12 has a larger muffler volume, it's going to be a little quieter than the RS-4. Performance-wise, there's going to be no discernable difference, even with a good dyno tune since both of these exhaust perform really well when compared to stock. If you're worried about noise, the RS-12 is a better option.

You'd probably find that just about any Ninja 650 aftermarket exhaust we sell is an improvement over the stock Kawasaki exhaust. This is down to the fact that OEM exhausts are rather heavy on account of the catalytic converter and also, the amount of internal baffling used in the muffler. Both of these are required to meet ever-tightening sound and gas emissions requirements. Also, if you want to get the best possible throttle response out of your bike, we highly recommend that you also adjust fueling to suit in the form of a Bazzaz Z-Fi fuel controller. That device, combined with the Yoshimura full system, will get you more power and the bike won't stumble when you grab a handful of throttle since fueling can easily be matched to the exhaust.