The present work is the numerical investigation of Spark Ignition (SI) engines to assess the effect of spark plug positions using open source Computational Fluid Dynamics (CFD) tool, OpenFoam is used. The standard k—ε turbulence model is used along with the Reynolds Averaged Navier Stokes equations for simulating the flow field. Average piston pressure is tracked for different Crank Angles (CA) from −180o to 180o for two different sized engines (560cc and 70cc). Results clearly show that spark plug position affects power output of engine. Spark plug position affect p-θ graph, hence performance of engine, this effect is dominant in bigger engine than smaller one. Spark plug position is expressed in dimensionless form in fraction away from centre