What's the point of a high compression ratio? A bigger power stroke captures more of the expansion that happens when fuel is burned, meaning you harness a greater amount of energy from the fuel.

Until now, high-compression engines faced a tough obstacle: knock, or premature ignition. Knock is an inefficient and potentially destructive combustion process where the heat and pressure in the combustion chamber cause the air/fuel mixture to ignite too soon.

Combat knock: It's not a Clash album, it's the job of an array of innovations in the SKYACTIV-G engine. These breakthroughs stave off excess temperatures in the chamber and speed up combustion to prevent knock, allowing the engine to achieve an astonishing 13.0:1 compression ratio on 87 octane gasoline. The Ferrari 458 reaches only 12.5:1 on premium. Rock on, Mazda.

Hot air: beloved by balloons and politicians, but an enemy of engine efficiency. Averting knock in a high-compression engine requires minimizing excess heat in the combustion chamber to avoid prematurely igniting the air/fuel mixture. So we developed a special 4-2-1 exhaust system with an extended pipe length that prevents the exhaust pulses from one cylinder pushing hot exhaust gasses back into another.

While the 4-2-1 exhaust system helps to prevent knock, it poses complications of its own. Because of the system's length, the emission-controlling catalytic converter normally wouldn't be able to reach the proper temperature quickly enough during cold starts.

To solve this, the exhaust is heated by slightly delaying the ignition timing. However, too much delay can cause unstable combustion. We came up with a novel solution: a cavity in the top of the piston that helps to stabilize combustion, even with delayed ignition.

The top of the piston is also dome-shaped. Not only does this make it look like a volcano, which is pretty cool, but it also helps to achieve high compression by reducing the volume of the combustion chamber.

Another method to improve knock resistance is to make combustion faster. Faster combustion means less time for the remaining air/fuel mixture to suffer those high temperatures, and that means less time for knock to rear its ugly head. The piston cavity also prevents the first milliseconds of flame from slowing itself down by hitting the top of the piston.

Another method to improve knock resistance is shortening the duration of the combustion. The faster the combustion, the shorter the amount of time the unburned air/fuel mixture is tossed around in those high temperatures. That means less time for knock to rear its ugly head.

With super-high fuel pressure of 2,900 psi, the SKYACTIV-G six-hole injector improves vaporization and cooling of the air/fuel mixture, and mixes up the fuel more evenly.

It also provides much faster injection, allowing the fuel delivery to be split into multiple injection events. This helps to optimize the distribution of fuel in the chamber.

We were so obsessed with achieving optimal combustion that we studied air movement patterns inside the cylinder. Using that knowledge, the spray of fuel was adjusted to make the air in the chamber move in a tumbling pattern, helping spread the fire faster once combustion starts.

After tackling thermal inefficiencies, we set our sights on cutting down friction and weight. Nearly every engine part and component was examined and redesigned to trim unneeded mass and reduce friction.

• Lighter pistons and piston pins (20% reduction)
• Lighter connecting rods (15% reduction)
• Reduced piston ring tensile force (37% reduction)
• Narrower crankshaft main journals (6% reduction in diameter, 8% reduction in width)
• Adoption of roller finger follower (greater than 50% reduction in valve friction)
• Adoption of compact electronic variable pressure oil pump (approx. 45% reduction in oil pumping loss)