Improving the performance of internal combustion engines requires a thorough understanding of the interactions among various engine parameters under dynamic operating conditions. This study investigates the effects of manifold roughness, geometric parameters (compression ratio and bore-to-stroke ratio), spark timing, and catalytic converter characteristics on the performance of a gasoline engine. Simulations were conducted over a speed range of 1000 to 6000 rpm using a parametric analysis framework. The novelty of this research lies in the comprehensive assessment of engine parameters and their combined impact on key performance indicators — torque, power, and brake specific fuel consumption (BSFC). A comprehensive engine model was employed to evaluate parameter variations, and optimal combinations for each performance objective were identified. The results demonstrated that simultaneous optimization of geometric parameters, ignition timing, and exhaust system characteristics enhances gasoline engine performance, such that at zero-degree spark advance, maximum torque and power were achieved at 4000 and 6000 rpm with a 5–8% reduction in BSFC, and in the optimal exhaust configuration with a volume of 40,000 mm³ and catalyst density of 100 CPI, the minimum BSFC of 0.258 kg/kWh was obtained at 3000 rpm.