Combustion engine

A four-stroke internal combustion engine, comprising:

• a combustion chamber;
• a piston mounted within the combustion chamber and configured to be sealingly engaged with walls of the combustion chamber, the piston being arranged for reciprocating motion along an axis between a first position in which the combustion chamber is of maximum volume and a second position in which the combustion chamber is of minimum volume;
• wherein the piston completes four strokes during a cycle, the strokes defined as intake stroke, compression stroke, combustion stroke and exhaust stroke;
• a fuel injection means in a region of the combustion chamber within the minimum volume defined by the piston in its second position;
• a cylinder head comprising an ignition means;
• an inlet cam configured to open and close an inlet valve;
• a No. 1 exhaust cam configured to open and close an exhaust valve;
• a No. 2 exhaust cam configured to open and close the exhaust valve that is configured to be opened and closed by the No. 1 exhaust cam;
• and
• wherein the No. 2 exhaust cam is angularly adjustable relative to the No. 1 exhaust cam in response to input from an operator, so that the No. 2 exhaust cam is able to be selectively engaged, wherein the No. 1 exhaust cam is configured to open and close the exhaust valve during the compression stroke, so that a selected quantity of air drawn in during the intake stroke is expelled during the compression stroke;
• wherein the No. 2 exhaust cam is configured to optionally close the exhaust valve when engaged;
• and
• wherein the fuel injection means is configured to adjust a quantity of fuel injected in accordance with the quantity of air retained during the compression stroke.