A four-stroke power valve is a device fitted to
four-stroke engine
A four-stroke (also four-cycle) engine is an internal combustion (IC) engine in which the piston completes four separate strokes while turning the crankshaft. A stroke refers to the full travel of the piston along the cylinder, in either directi ...
s that constantly adjusts the internal diameter of the exhaust system to better suit the speed of the engine.
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.
Later versions from ]Honda
is a Japanese public multinational conglomerate manufacturer of automobiles, motorcycles, and power equipment, headquartered in Minato, Tokyo, Japan.
Honda has been the world's largest motorcycle manufacturer since 1959, reaching a producti ...
went by the names Honda Titanium Exhaust Valve (HTEV) and Honda Variable Intake/Exhaust (H-VIX),[ appearing on the CBR600RR and ]Honda CBR929RR
The Honda CBR900RR, or FireBlade in some countries, is a sport bike, part of the CBR series introduced in 1992 by Honda. It was the first of a series of large-displacement Honda models to carry the RR suffix. The development of the first gener ...
. Suzuki
is a Japanese multinational corporation headquartered in Minami-ku, Hamamatsu, Japan. Suzuki manufactures automobiles, motorcycles, all-terrain vehicles (ATVs), outboard marine engines, wheelchairs and a variety of other small internal co ...
's version is called Suzuki Exhaust Tuning (SET).[ The system is also used on the Triumph Daytona 675 triple.
]
Operation
At low engine speeds, the wave pressure within the pipe network is low. A full oscillation of the Helmholtz resonance
Helmholtz resonance or wind throb is the phenomenon of air resonance in a cavity, such as when one blows across the top of an empty bottle. The name comes from a device created in the 1850s by Hermann von Helmholtz, the ''Helmholtz resonator'', wh ...
occurs before the exhaust valve is closed, and to increase low-speed torque, large-amplitude exhaust pressure waves are artificially induced. This is done by partial closing of an internal butterfly valve within the exhaust where the primary pipes from the cylinders join. The alteration of the pressure at this point controls the behavior of reflected waves at this sudden increase in area discontinuity. Closing the valve increases the local pressure, inducing the formation of larger-amplitude negative reflected expansion waves. A servo motor controlled by the ECU opens and shuts the valve.
See also
* Exhaust manifold
In automotive engineering, an exhaust manifold collects the exhaust gases from multiple cylinders into one pipe. The word '' manifold'' comes from the Old English word ''manigfeald'' (from the Anglo-Saxon ''manig'' anyand ''feald'' old and ref ...
* Kadenacy effect
Notes
{{DEFAULTSORT:Four stroke power valve system
Motorcycle engines
Exhaust systems