Reed valve

Reed valves, normally a leather flap covering a hole, are amongst the earliest form of automatic flow control for liquids and gases.

[1] The Swedish motorcycle company Husqvarna produced a two-stroke, 500 cc displacement single cylinder engine with a reed-valve controlled intake, one of the biggest in using this arrangement.

Toyota discovered the benefits of injecting fresh air into the Wankel RCE exhaust port, and also used a reed valve in prototypes where they tested the SCRE concept (Stratified Charge Rotary Engine).

According to David W. Garside, who developed the Norton line of Wankel-powered motorcycles, data from other RCE producers pointed that reed valves do improve performances at low rpm and under partial load, but reduce the high speed power output of the engine, a feature considered inconvenient for motorcycle engines.

Once the charge has expanded and mostly left the engine, pressure inside drops again to below-atmospheric values and the reed valve allows fresh air to enter and the cycle be repeated.

Some ram-air pressure due to forward motion helps scavenging and filling the combustion chamber with the new, fresh air charge, thus improving the power of the engine at higher speeds.