We referred to automobile engine combustion technology, with its complementary focus on the low and middle rpm ranges, to improve fuel efficiency but still deliver a powerful ride through surer combustion. In engines where the aim is to boost output, it has been common practice to prioritize intake efficiency in the high rpm range. In our engine, however, where the non-conventional emphasis was on the low and middle rpm ranges, we focused on low- and mid-range rpm combustion efficiency instead of high-rpm intake efficiency. The result was Φ73X80mm bore and stroke.
Sure and stable combustion in the low and middle rpm ranges was achieved by marrying this ideal bore and stroke combination with an ideal shape for the combustion chamber and optimal valve timing. Furthermore, core research into idle combustion using a similar engine with the same level of displacement accumulated the basic data required to achieve stable stoichiometric (theoretical air-fuel ratio) combustion. Effecting stoichiometric combustion from idle rpm was a significant contributory factor to the engine's superlative fuel efficiency.