The cup allows faster combustion and shortens the time any unburned air/fuel mixture in the rest of the cylinder is exposed to high temperatures, thus reducing the risk of detonation. The cup acts like a mini-combustion chamber and allows the flame front to spread quickly when fuel is injected directly into this recessed cup in the top of each piston. However, the pistons are domed like a performance piston to raise compression, and have a small cup in the top similar to a diesel piston. There are four pistons, 16 valves (four per cylinder) and one platinum spark plug per cylinder with a coil-on-plug ignition system. It has an aluminum block and cylinder head, with a pair of chain-driven overhead cams. Their solution was to reduce the temperature and pressure inside the combustion chamber by carefully managing the running compression of the engine via VVT, by precisely timing and aiming the direct fuel injection pulses into the combustion chamber, and by extracting heat as quickly as possible from the engine with a long tube 4-2-1 exhaust manifold.Ī SKYACTIV-G engine is pretty similar to any other engine.

They knew that a higher compression ratio would increase fuel efficiency and economy, but that detonation would be a problem if the temperature and pressure in the combustion chamber was too high for regular gasoline or even premium pump gas. Mazda engineers knew this when they designed their new SKYACTIV-G engines. Consequently, they have to burn some type of high-octane racing fuel to minimize the risk of detonation.

However, most racing engines are carbureted or port injected and do not have direct injection or Variable Valve Timing (VVT). With 112-octane racing gas, the compression ratio can be bumped up to 14 or 15:1. Leaded racing fuel rated at 107 pump octane can usually handle compression ratios in the 12:1 range. These engines are burning super high-octane racing gas or some type of alcohol (methanol or E85 ethanol) and have rich air/fuel mixtures. Many high-performance racing engines run compression ratios of 14:1 or higher, but not on ordinary pump gas. So how can Mazda SKYACTIV-G engines burn regular 87 octane gasoline with a static compression ratio of 13:1? It’s Mazda magic! If the fuel lacks enough octane to handle a higher compression ratio, it will detonate, knock and cause a loss of power - and possible engine damage, too!

Raising the compression ratio of a gasoline engine also improves its thermal efficiency, power output and fuel economy.īut as compression goes up, so do the octane requirements of the fuel to resist detonation. Diesel engines are typically about 30% more efficient than gasoline engines partly because of their significantly higher compression ratios (16:1 or higher for diesels versus 9:1 or 10:1 for most gasoline engines). The secret to Mazda’s fuel economy gains with its SKYACTIV-G engines is in its approach to combustion management. These engines include the SKYACTIV-G 1.3L engine in the 2012 Mazda 2, the 2.0L in the 2012 Mazda CX-5, and the 2.0L and 2.5L engines in the 2014 Mazda 6 and CX-5. Introduced in 2011 in the Japanese market, Mazda’s ultra high-compression, direct injection gasoline engines are achieving fuel economy numbers that rival many hybrids - and at much less cost.

Mazda toolbox sucks