Development Aim
In this system a variable EXUP valve is placed in the muffler that functions in accordance with engine rpm to control the reflection wave cycle in the muffler. It was developed to help optimize the exhaust flow in the exhaust valve area in a way that makes the exhaust as well as the intake function more efficient and reduces power loss due to the “blow-back” phenomenon. It is a device that in effect creates an adjustable valve that changes the cross-section shape of the interior of the muffler depending on engine rpm to improve performance.

Structure and Function 
In order to achieve greater accuracy, the system on the YZF-R1 functions on readings of five parameters:
(1) engine rpm,
(2) speed,
(3) degree of throttle opening,
(4) speed of throttle motion and
(5) gear position.
This information is processed by the control unit and, while also being relayed to the ignitor unit so it optimizes the ignition timing, the information is used to operate the EXUP valve to regulate the exhaust pressure wave and in that way improve intake efficiency. This helps achieve optimum response over a wide rpm range from low to high speeds.

Effect 
1) Realizes elimination of low torque in certain rpm ranges and smooth acceleration all the way up to high speed.
2) Improved actual fuel economy.
3) Improved low-speed range combustion for
(1) more stable idling,
(2) less idling noise and
(3) reduced HC levels in the exhaust.