One of the biggest internal combustion engines in the world , the WÃ rtsilÃ - Sulzer RTA96-C is a two-stroke ; it is bigger than most two-story houses , has pistons nearly 1 metre in diameter and is one of the most efficient mobile engines in existence . One of the biggest internal combustion engines in the world , the WÃ rtsilÃ - Sulzer RTA96-C is a two-stroke ; it is bigger than most two-storey houses , has pistons nearly 1 metre in diameter and is one of the most efficient mobile engines in existence .