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The spark ignition engine is the most widely used in land transport sector. Hence, studies to predict and improve its behavior continue to be essential. The behavior of the intake and exhaust systems is important because these systems govern the air flow into the engine's cylinders. Inducting the maximum air flow at full load at any given speed and retaining that mass within the engine's cylinders is a primary design goal. The higher the air flow, the larger the amount of fuel that can be burned and the greater the power produced. The important parameter is the volumetric efficiency along with equal air flows to each engine cylinder. The valves and ports, which together provide the major restriction to intake and exhaust flows, largely decouple the manifolds from the cylinders. In this work it was intended to find out the effect of variable valve lift and throat diameter on the performance of the SI engine, namely volumetric efficiency, power, brake specific fuel consumption, and pollutants. Hence, it contributes toward having greener cars in the future. A specially designed computer program (Lotus) was used to predict the gas flows, combustion and overall performance. The results of this investigation show that increasing the valve lift is relatively more effective than throat diameter in boosting volumetric efficiency and power and reducing specific fuel consumption, nitrogen oxide and carbon monoxide emissions. A 10% increase in valve lift resulted in an improvement of 1.8% in η v , 3.3% in power and a decrease of 1.5% in BSFC and (0.3–0.8)% in engine emissions. However, a 10% increase in valve throat diameter causes 50% less effects than the valve lift.