Abstract: A two stroke internal combustion engine (5) having a transfer port (9) and an exhaust port (8) in a cylinder (6) which are opened and closed in a timed relationship by the reciprocating movement of a piston (7). The exhaust port (8) communicates with an exhaust passage that is tuned to provide a pressure pattern in the exhaust passage that will create at the exhaust port (8) a predetermined pressure pattern while the exhaust port (8) is open. Coolant is supplied to the exhaust passage when the engine is subject to increasing transient load conditions, at engine speeds below the tuned speed, and at a controlled rate to establish a tuned state in the exhaust passage during the transient condition.