An experiment was carried out in a dedicated compressed natural gas direct injection (CNG-DI) engine with a compression ratio (CR) of 14 and a central injection system. Several injection timing parameters from early (300° BTDC) to intermediate (180° BTDC) to late injection (120° BTDC) were investigated. The 300° BTDC injection timing experiment was carried out to simulate the performance of port injection engine and the result is used as a benchmark for the engine performance. The late injection timing resulted in a 20% higher performance than the early injection timing for low engine speed up to 2750 RPM. Intermediate injection timing shows the highest performance over an extensive range of engine speed because the 180° BTDC injection timing has a similar volumetric efficiency as in late injection timing. However, the earlier injection events allowed for a better air-fuel mixing. The early injection timing gives superior performance for engine speed above 4500 RPM. This could be attributed to the fact that the penalty of the reduction in volumetric efficiency is compensated by the increase in mixing time for the air-fuel mixture.