AmSnow.com is now SnoWest.com
The EXUP system features a computer-controlled butterfly valve located in the exhaust system to regulate the exhaust pressure waves regulating the flow of positive and negative pressure waves in the system and improving cylinder scavenging at all engine speeds. The wedge-shaped valve is located at the downstream end of the 4 header pipes where they enter the exhaust collector. The valve is operated by a servomotor and is regulated by the ignition computer.
Sensitive to engine speed, the EXUP valve is almost entirely closed at low rpm and gradually opens to permit unrestricted gas flow at high rpm. Improvements include smoother and quieter idle, more power at all rpm, significant low-range and mid-range torque increases, and higher gas mileage. By gradually opening the valve as revs increase, the positive wave in the mid-range is eliminated, yet the exhaust system can "breathe" fully at high revs for maximum power."
Now you know!