{HEAD ~ The intake and exhaust control systems} are operable in {TAIL ~ varying modes}, according to the engine speed, by a single actuator 
are operable in
{ HEAD ~ The intake and exhaust control systems } are operable in { TAIL ~ varying modes } , according to the engine speed , by a single actuator
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH