the valve controller reference is an Idle air control valve, not the intake or exhaust valves, as you correctly say these are activated by the belts
http://www.amazon.co.uk/Idle-Air-Control-Valve-22650AA192/dp/B00LN28FWO
where as the boost controller controls how much pressure builds up in your intake system
http://www.amazon.co.uk/Subaru-Impreza-Manual-Boost-Controller/dp/B001MMY87Q
please note these links are for illustration purposes I am not recommending them or the source