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