This work aims at evaluating a proposed technique for NOx reduction and knock control in spark ignition engines. The proposed technique is based on adding a secondary chamber equipped with a piston to the engine combustion chamber. The volume variation of the secondary chamber, resulting from the motion of the secondary piston, should be tuned to the combustion process in the engine. The phenomenological analysis of the proposed technique showed that the achieved outputs come out as a result of three mechanisms. These mechanisms are; control of the heat release rate inside the engine, combustion staging and enhancing turbulence inside the engine, especially at the later stage of combustion. The later ensures complete combustion inside the engine. The proposed technique proved to be more effective than exhaust gas recirculation (EGR) where it reduces NOx emissions while improving engine specific power. The synergy between the proposed technique and exhaust gas recirculation has proved to be useful where it improves the later by reducing NOx emissions by 70% at only 2.5% of EGR, while the power is reduced by only 3%.