alpha Racing's SAS valve cover set (2 pcs.) for blocking off the "Secondary Air System" ("SAS") in BMW S1000RR/HP4 at the valve cover. The BMW Secondary Air System is an induction system that burns the unburnt exhaust gases by injecting fresh air (secondary air) into the exhaust ports of the engine, reducing the emission of hydrocarbons. Once these are capped off with the alpha Racing block off plates for the AIRBOX (sold separately), and VALVE COVER, the air injection system including the canister, piping and fittings can be safely removed. alpha Racing's SAS Block Off Plates are made from CNC billet aluminium, have an OEM O-ring for correct seal and feature the “alpha” logo. For racing use only. If you are using your motorcycle on a closed course (racing, track days, etc.) you will want to remove all unnecessary equipment from your bike for reduced weight and ease of maintenance. To get an accurate Air:Fuel (A/F) ratio when you dyno the bike. The air injection system pumps fresh air directly into the exhaust stream in order to burn off any unused fuel. Unfortunately by doing this the A/F ratio is thrown off by the extra "fresh air" in the exhaust stream. By removing the air injection system you can achieve an accurate A/F ratio. This addition will typically remove the majority of popping on deceleration that can be experienced with un-burnt gasses within the emission charcoal chamber. Proper tuning is required.