TWB S1R Muffler and Juice Box
The engines of modern sport bikes are equipped with a number of systems (EXUP, AIS, catalytic converter) and tuned to meet current CO and noise standards. For sport motorcycles used on tracks and lots, compliance with standards isn't required, while weight reduction, individual tuning and more power are highly desirable. Fitting a straight-through muffler is the easiest and fastest way to shed a few kilograms by removing the valve mechanism, the catalytic converter and the heavy stock can.
On some motorcycles removing the valve throws an error, which can be cleared with an eliminator. Removing the catalytic converter and valve noticeably affects engine operation, since the stock fuel map (mixture versus engine speed) is tuned for the stock system. This can show up as an unstable idle, backfires when you snap the throttle shut or a jerky power delivery. Most street riders don't pay attention to this, because it doesn't fundamentally change the feel. But for athletes such changes are unacceptable, and increasing power is also very important.
To adapt the fuel map to the new straight-through system, you need to install a fuel controller that replaces the stock map with a tunable one. Such controllers usually come with a set of maps for different motorcycle models and exhaust configurations. In that case it is enough to load the right map without tuning. Professionals chasing fractions of a second on the track tune each motorcycle individually, since all engines are different, but this doesn't make a noticeable difference and isn't needed for semi-professionals. There are many controller manufacturers. All of them are made for a specific motorcycle model. The Juice Box power controller has several preloaded maps, so when fitting a Two Brothers system you don't need to connect the controller to a computer and load a map. The unit is compact and easy to install.
Watch the detailed video on installing a Two Brothers S1R muffler and a Juice Box fuel controller on a 2009 Kawasaki ZX-6R.