Back to the future for turbocharged Mazda

IT IS no stranger to the engineering art of forced induction, but the initial decision by Mazda to avoid the siren song of turbocharging its SkyActiv petrol engine range has been turned around, thanks to the size of its new CX-9.

The second-generation seven-seater, which weighs in at more than 2000kg, will herald the introduction of a turbocharged version of the company’s 2.5-litre inline four-cylinder petrol engine, replacing the existing Ford-derived 2.7-litre V6.

It’s the first Mazda passenger vehicle to use a turbo motor since the Mazda3 MPS went out of service in 2007 the BT-50 commercial ute range is powered by a pair of Ford-sourced turbo-diesels.

In Australia, Mazda has sold turbocharged versions of the Mazda3 MPS, Mazda6 MPS and MX-5 SE, along with a limited number of RX-7 SPs in the mid-1990s.

From a technological standpoint, Mazda engineers have based the new engine on the naturally aspirated 2.5-litre SkyActiv G, retaining that engine’s displacement, bore and stroke measurements, along with fuel system components like the direct-injection fuel injection system and fuel pump.

The new turbocharger uses technology that Mazda claims is an industry first.

Instead of using variable vanes on the impeller to control exhaust gas flow to the turbine, Mazda instead controls the output of the engine’s exhaust valves to modulate gas flow into the turbo.

At low revs (under 1620rpm), a set of valves in front of the turbine close down, forcing gas into the inlet at a greater pressure to spool the turbo up quickly and overcoming throttle lag.

At higher revs, the valves open again to allow a full charge of exhaust gas.

The system is helped by a unique 4-3-1 exhaust header arrangement that provides a constant stream of exhaust gas for the turbo to use, while an exhaust gas recirculation system lowers engine air intake temperatures by up to 400 degrees C.

As well, engineers have managed to give the engine a very high 10.5:1 compression ratio, which allows the use of lower-octane fuel without the danger of engine-wearing pre-ignition, or knock.

The result is an engine that produces up to 186kW at 5000rpm on high-octane fuel, or 169kW on lower octane-rated fuel. Torque is rated at 420Nm at 2000rpm.

No fuel consumption or emissions figures have been provided.

There is little doubt that the new engine – dubbed the SkyActiv G 2.5T – will make its way under the bonnet of future Mazda products developing a new engine is an expensive process, and the cost will need to be amortised across multiple platforms and applications.

Given that the packaging requirements are largely based on an existing powerplant, the turbocharged engine could be seen in a wide array of vehicles from the Mazda3 and Mazda6 as well as the CX-5.

Mazda’s latest version of its clever, compact and robust computer-controlled permanent AWD system also adds a piece to the performance puzzle it is already fitted to the diminutive CX-3 as well as the CX-5, so could easily be used on Mazda3 and Mazda6.

As well, a performance version of the forthcoming CX-4 coupe-esque crossover SUV would be warmly received in Australia.

Mazda Australia marketing director Alastair Doak told GoAuto at the launch of the CX-3 earlier this year that the company had changed its focus when it came to performance powerplants.

“We’d certainly look at turbocharging petrol engines for more performance instead of using something like a V6,” Mr Doak said when asked about turbocharging future generations of Mazda petrol engines.