Pinned EXUP - Exhaust Ultimate Powervalve - Information and Maintenance

Yamaha was the first to develop such a system, called the Exhaust Ultimate Power Valve (EXUP). It first appeared on the Yamaha FZR EXUP and was later used on many other Yamahas.

It changes exhaust tuning as rpm increases. Many highly tuned 4-stroke engines with four-into-one exhaust systems have a flat spot in the mid-range, precisely where the sporting rider needs instantaneous throttle response. This flat spot is caused by positive resonance pressure waves forcing the spent exhaust gases back into the combustion chamber during the valve "overlap" period (when both intake and exhaust valves are open). These exhaust gases dilute the incoming intake mixture, decreasing performance significantly… causing a flat spot or bog. This generally occurs only in the mid-rpm range. At other engine speeds, the positive pressure wave arrives when the exhaust valve is closed and therefore cannot dilute the intake mixture.

The EXUP system features a computer-controlled butterfly valve located in the exhaust system to regulate the exhaust pressure waves. The EXUP system regulates the flow of positive and negative pressure waves in the system to improve 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 rpms, 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.







EXUP Maintenance
http://www.cartestsoftware.com/fz1/exupmaintenance.html


EXUP servo to TCI connection - 3LN1




3LN1 EXUP servo cycle at kill switch on (noise is fuel pump priming)

 

A dismantled EXUP