Small turbodiesels were way ahead of small gasoline engines for decades in fuel economy, power, and so forth. Diesel, which uses direct injection and compressio

Small turbodiesels were way ahead of small gasoline engines for decades in fuel economy, power, and so forth. Diesel, which uses direct injection and compression ignition, has always been a natural fit with turbocharging, which makes them intrinsically suited to the paradigm of a small engine for efficiency with a turbo for power. They also intrinsically have great low-end torque, which complements the top-end power of turbos. Turbo gasoline engines were hard to make well, I gather mostly due to predetonation. Gasoline engines historically use manifold injection and spark ignition, which limits compression ratios. However, with advances in technology, particularly in engine computers & sensors, small turbo gas engines have recently become far more competitive. So, basically, from the vantage point of 2018 turbodiesels might seem like a questionable choice- but ten or twenty years ago, good small turbocharged gasoline engines mostly didn't exist.