Mazda Skyactiv engines explained

With the new Skyactiv-X, Mazda has a trio of ways to show the internal combustion engine is not dead.

Brian Cooley Editor at Large
Brian Cooley is CNET's Editor at large and has been with the brand since 1995. He currently focuses on electrification of vehicles but also follows the big trends in smart home, digital healthcare, 5G, the future of food, and augmented & virtual realities. Cooley is a sought after presenter by brands and their agencies when they want to understand how consumers react to new technologies. He has been a regular featured speaker at CES, Cannes Lions, Advertising Week and The PHM HealthFront™. He was born and raised in Silicon Valley when Apple's campus was mostly apricots.
Expertise Automotive technology, smart home, digital health. Credentials
  • 5G Technician, ETA International
Brian Cooley
2 min read

Carmakers are rolling over on combustion engines at a rapid clip: You won't hear them crowing about their latest combustion technology nearly as much as their latest way to use a battery and an electric motor. But Mazda cuts the other way with a set of engines whose name sounds like an ISP or a yoga studio, not some of the most clever technology under any hood.

Watch this: What does Skyactiv tell you about a Mazda engine?

Skyactiv-G (Gasoline) is a modern take on a holy grail: The high-compression engine. Such designs compress air and fuel in the cylinder to a higher degree before lighting it off, generating more power from a given amount of fuel. But high-compression engines tend to combust chaotically, leading to spark knock, which threatens an engine's efficiency and longevity. Mazda has conquered that by putting a little combustion well atop the piston, injecting fuel in precise, fast bursts so it has less time to get into trouble, and by carefully scavenging exhaust with a 4-2-1 header system.


Mazda's Skyactiv-G piston has a critical little well in the top of its domed pistons to help control pre-detonation at very high-compress ratios.


Skyactiv-D (Diesel) is their take on the diesel, an engine that has always used high compression to cause spontaneous combustion of air and fuel without a spark plug. But Mazda lowers that ratio to give the squirt of diesel fuel more time to mix with air before it detonates. That, along with precise spritzing of the fuel leads to a cleaner, more thorough burn. The lower compression ratio means the engine can use somewhat lighter parts and slightly looser tolerances for less energy-sapping friction and weight.


Mazda's Skyactiv-D technology runs a slightly lower compression ratio than traditional diesel to give the injected fuel a little more time to mix thoroughly with air in the cylinder (seen at right) for more complete fuel utilization and fewer emissions.


Skyactiv-X (Gasoline X Diesel) is a gas engine that works like a diesel: It relies on high compression to cause the air/fuel mixture to combust, but retains a traditional spark plug to fine tune the nature of that combustion. It also runs lean, inhaling relatively more air than fuel, which would normally result in a miserable little econobox engine but, in this case, the high compression makes up for the power lost to that burn. And, since it uses relatively more air than gas, it can be run at high, sportier RPMs and avoid boring tall gears while still preserving good MPG. It debuts on Mazdas in the EU first, but we have a first drive for you here.