The Double Six is named after a taxable RAC rating of 50 hp, but the modern rating is somewhere between 130-150 bhp. Less then 10 cars were ordered with the Double Six 50 engine.
Built in four banks of three cylinders, each block of the Double Six engine was independent with its own cooling, intake and exhaust system. It could be ordered in a variety of sizes and the option of regular poppet valves was available for more conservative customers. For others that were more ambitious, the seven liter Double Six 50 was the best, but only a few cars were ordered with it. Since these had one of the most complex motorcar engines ever made, they demanded equally as dramatic coachwork to surround it.