With the world’s automakers and mainstream media’s hard-on for uber-efficient electric vehicles (EVs) and autonomous driving these days, one could be forgiven for thinking the future of driving enjoyment looks bleak. But don’t despair; not all automakers are turning their backs on the combustion engine and driver enjoyment — well, not anytime in the next 40 years, if we can believe everything we’re told in press releases from Mazda. Instead of going all volts and amps, the Japanese automaker is focusing on pushing the efficiency of four-cylinder internal-combustion engines to new heights without sucking all the fun out of driving, and, better still, its new motor will be offered in true manual form. The Skyactiv four-cylinders are nothing new, having been available from Mazda since 2011, but, set for release in 2019 is the most advanced version so far — the Skyactiv-X. The carmaker’s aim is to to battle the onslaught of EVs with super-efficient four-cylinder technology that retains some throttle-induced fun. It’s a first for petrol engines: a 16.0:1-compression two-litre four-cylinder offering up some interesting advancements that are truly game-changing and will push the humble combustion engine well outside its current comfort zone of a 14.5 air–fuel ratio (AFR), well into the lean zone of AFRs in the 30s (yes, the 30s) during light throttle applications.
This is possible due to the homogeneous-charge compression ignition system, which uses compression to combust the mix rather than spark, just like a diesel. It’s something that had never been used in a gasoline engine successfully until Mazda developed its spark-controlled compression ignition, which is a hybrid of compression and spark ignition that uses a small supercharger to control the compression ratio and AFR. Simply relying on the compression to combust the mix is too uncontrollable with petrol, as it enters the combustion chamber mixed with the air and will pre-ignite. Unlike a diesel, which controls combustion by adding the fuel directly into the chamber at precisely the right time, which is why Mazda’s system uses a combination. At low rpm — that is, light throttle — a tiny spark is used to kick off combustion, while compression finishes the job. This allows a lot more air to be present in the chamber. At high rpm, the mixture is richer and switches to conventional spark ignition. The combination is said to be 30 per cent more efficient than Mazda’s already-efficient 2013 model.
There is also some very trick, tuned-length, four-into-two-into-one, long-runner headers, which, as in any race engine, play the key role of scavenging exhaust gases. Header length also helps with the torque curve, or, more important, flattening it out so that the fun lasts all the way from 2000 to 7000rpm. Power figures on the pre-production machines are estimated at equal parts power and torque, with both in the 170 range. With the Skyactiv-X due out in the Mazda line-up next year, we won’t have to wait long to see how the Mazda 3s and 6s perform in real life. Did someone say endurance race car?