This study was carried out to evaluate the variation in performance and emission characteristics of a multi cylinder Multi-point Fuel Injection (MPFI) automotive Spark Ignition (SI) engine after incorporating an additional manifold for gas injectors to throttle body. To install gas injectors for Compressed Natural Gas (CNG)/Hydrogen-CNG (HCNG) operation throttle body of the engine was modified using a novel manifold. The performance and emission characteristics of the existing throttle body and the new throttle body configuration were evaluated. The parameters studied were Manifold Air Pressure (MAP), Torque and Emissions (HC, CO, CO2, and NOx) for gasoline operation. The influence of installing new manifold on these parameters was evaluated. It was important to evaluate the degree of variation of the parameters on the gasoline operation so that the addition of new manifold for gas operation could be validated. The measurement was carried out at wide open throttle. There was negligible variation in power and torque characteristics for the new configurations. There was no significant change in the emission characteristics. The modified throttle body configuration demonstrated good overall performance.