The 2.5-litre 250 PS at 5,000 rpm (227 hp for Japanese market version) and 420 Nm (at 2,000 rpm) SkyActiv-G 2.5T engine will replace the previous CX-9’s Ford-sourced 3.7-litre naturally aspirated V6 engine.
While many turbocharged engines use variable geometry turbine turbos, Mazda have opted to develop its own alternative solution to combat turbo lag – a major problem with turbocharged engines.
Mazda’s solution is called Dynamic Pressure Turbo, a world’s first system that allows the SkyActiv-G 2.5T to vary the degree of exhaust pulsation depending on engine speed.
At low rpms (below 1620 rpm), the volume of the exhaust ports is reduced by closing a series of valves located just before the turbine that drives the turbocharger. Mazda says this solution reduces interference between exhaust pulses and maximizes the energy of each pulse to obtain a high turbine driving force. At higher rpms there is sufficient energy in the exhaust flow and the valves open, allowing the turbine to be driven by a steady flow of exhaust gases as in a traditional turbocharger.
While naturally aspirated SkyActiv-G engines have a compression ratio of between 14.5:1 to 15.0:1, the SkyActiv-G 2.5T has a lower 10.5:1 compression ratio due to its turbocharging. The figure is still very high for a forced induction engine – Mazda says it’s one of the highest for turbocharged engines, and that it still runs on regular petrol.
The engine’s bore size is the same as regular naturally aspired SkyActiv engines, at 89 mm.