The Mazda Z engine range features a number of gasoline inline-four engines. They use a cast iron block to provide good strength and are available in a wide range of displacements.
The 74bhp, 89bhp and 113bhp engines accelerate to 62mph in 12.1sec, 8.7sec and 8.6sec respectively. The 115bhp model is a touch quicker but still needs to be floored at motorway speeds.
Mazda’s SKYACTIV-X is a defining moment for the motoring industry. It employs a method of combustion that the world’s top carmakers have been trying to perfect for over two decades.
The engine combines the best of both gasoline and diesel engines, with the efficiency and low-RPM grunt of diesels and the high-RPM responsiveness of gas. It also uses a unique ignition system that mimics the compression ignition of diesels, but with spark plugs instead of piston rings.
What’s more, the SKYACTIV-X runs extra lean in order to make the most of its compression ignition. This means there’s plenty of air in the cylinder, often more than twice as much air as a conventional petrol engine.
What’s most impressive is that it handles this extra pressure with regular 87 octane fuel. It won’t benefit from higher-grade 93, which could mean more performance or better mpg.
The Skyactiv-G engine is a modern take on the high compression engine. Its 14:1 compression ratio is a first among gasoline engines in production, and it compresses air/fuel mixture to a greater degree before lighting it off, generating more power.
But this method can be problematic: it creates excess heat, which leads to spark knock that can degrade engine efficiency and wear out components. Mazda has addressed this problem by using cooled exhaust gas recirculation to keep combustion temperatures down.
It also uses an advanced direct-injection system that delivers fuel in fast, precise bursts. This enables the engine to deliver higher power output and fuel economy without having to sacrifice torque or horsepower.
In addition to engine technology, the SKYACTIV-G also has an improved cooling system and an efficient fuel pump to help reduce consumption. It even features cylinder deactivation to shut off cylinders in light-load situations when the car is coasting. This translates to a remarkable EPA-estimated 30+mpg city and 40+mpg highway in the 2.0-liter model we tested.
The 2.0-litre SKYACTIV-M engine is a mild hybrid system that uses more air and less petrol than a conventional engine to create fewer emissions. It’s joined by a belt-driven integrated starter generator (ISG), which functions as an electric motor when you decelerate and is powered from a 24V battery.
Depending on the driving conditions, it switches between two- and four-cylinder operation and shuts down cylinders one and four in light load situations such as when cruising at a constant speed. The cylinder deactivation is controlled precisely to avoid any loss of power.
Mazda engineers have developed a new type of ignition that combines the efficiency and low-RPM grunt of diesel combustion with the high-RPM responsiveness of gasoline. This is called Spark Controlled Compression Ignition, or SPCCI for short.
SKYACTIV-E delivers fuel efficiency up to 20-30 percent better than the gasoline engine used in Mazdas today. It does so through a new technology known as Spark Controlled Compression Ignition (SPCCI).
Using conventional spark ignition, SPCCI ignites a small fraction of the air-fuel mixture, which then squirts into a hot combustion chamber where it spontaneously combusts under pressure. The result is a diesel-like power output and high torque, without the downsides of emissions.
SKYACTIV-D also features SPCCI, but instead of injecting the air-fuel mixture with a spark plug to control it, it uses high compression to cause spontaneous combustion and then spritzes the mixture with precise squirts of fuel. The result is a powerful engine that offers 30 per cent more torque and is much less polluting than a standard SkyActiv G 2.0-litre petrol.