What is Skyactiv? Marketing speak, of course. It is the single word Mazda has invented to represent a diverse spread of technologies and strategies aimed at improving efficiency. As such, Skyactiv has a different meaning depending on whether you’re talking about engines, transmissions, chassis, or the vehicle’s body.
The most significant piece of Skyactiv-branded hardware is the 2.0-liter Skyactiv-G (G for gasoline) engine. It stands to be the volume powerplant under the hood of Mazda’s core vehicles--the compact Mazda 3, the next Mazda 6 mid-size sedan, and the new CX-5 crossover. Compared with the engine it replaces, the Skyactiv-G delivers a 15 percent improvement in both torque and fuel economy.
Rather than improve efficiency with an external aid like a turbocharger or an electric motor, Mazda has devoted its development resources to optimizing the internal-combustion process. The core tenet of the Skyactiv-G is an exceptionally high compression ratio of 13:1*—higher than that of the Ferrari 458 Italia’s power-dense, normally aspirated V-8. A higher compression ratio improves efficiency, but it also means raised cylinder temperatures, which lead to increased emissions and a greater chance of catastrophic detonation or preignition. Mazda’s ability to manage the heat is what transforms the theory of a higher compression ratio into road-going Skyactiv technology.
Direct injection--in all applications, including the Skyactiv-G--provides a cooling effect to the intake charge as fuel evaporates upon entering the cylinder. The shape of the piston cavity and the fuel distribution of the six-hole injectors promote quicker combustion, meaning there’s less time for the air/fuel mixture to detonate before it’s ignited by the spark-initiated flame front. A wicked-looking 4-2-1 exhaust manifold also plays a key role by maximizing the amount of hot waste gas removed during the exhaust stroke and preventing it from flowing into an adjacent cylinder.
At low loads, Mazda performs a valve-timing trick to effectively lower the compression ratio while maintaining the long, power-producing expansion stroke. Electronically adjustable intake valves close later than in a typical engine (characteristic of the Atkinson cycle), and excess air is pushed out of the cylinder and back into the intake manifold before combustion. This allows the throttle to be held open at wider-than-usual angles to reduce the pumping losses that afflict all throttled engines. To compensate for the diminished low-end torque caused by the Atkinson cycle, engineers reworked the dimensions of the 2.0-liter engine, stretching the piston stroke by 8.1 millimeters. Mazda also claims a 30 percent reduction in internal friction with the Skyactiv-G due to a number of incremental improvements including shorter piston skirts, a more efficient water pump, and roller finger followers on the valvetrain rocker arms.
While the technology behind Skyactiv isn’t nearly as tangible or as easily understood as hybridization or the downsize-and-boost strategy, it produces measurable results. In the 2012 Mazda 3, the Skyactiv-G model returns 28/40 mpg compared to 24/33 mpg with the existing 2.0-liter engine. As an added benefit, when Mazda does eventually turn to turbochargers and electric motors for additional power or efficiency, the cars stand to benefit from the combustion optimization work that has already been completed.
*In most markets, the Skyactiv-G 2.0-liter engine boasts a compression ratio of 14:1 but requires higher-octane gasoline. The 2012 Mazda 3 with Skyactiv-G has a compression ratio of 12:1 because the 4-2-1 exhaust manifold doesn’t fit in the engine bay. Sources say the next Mazda 3 should have the fancy exhaust setup and the higher 13:1 compression ratio.