Mazda changes turbo tune

Forced induction no longer a sign of an inefficient engine. Now it’s SkyActiv-approved

DAMION SMY

A TURBOCHARGED Mazda will be in showrooms in 2016, despite the fact that the company has publicly dismissed turbocharging for its frugal ‘SkyActiv’ petrol engines.

While the rest of the global automotive industry reduced engine size, swapping cylinder count for forced induction, Mazda has been steadfast in producing higher capacity, high-compression engines without the need for artificial aspiration. “A turbo and downsizing is a temporary solution to not having the right engine in the car in the first place,” said Robert Davis, Mazda’s senior vice president of R&D back in 2011.

Now, Mazda has wheeled out the all-new CX-9, its seven-seat flagship, with a 2.5-litre turbo size f s cap wi as havi t Dav o Ma cylinder engine in place its predecessor’s 3.7-litre 60-degree V6. So why did it choose turbocharging?

“SkyActiv is not an engine, a single thing,” says Mazda Development Engineer, Dave Coleman, “it’s a philosophy, a way of approaching what you’re after.” Those goals for the CX-9 included greatly four-c of it 60 ch a a t improved torque on the production of the core SkyActiv weight saving That put the previous V6 on death row.

“What we’re engine strategy absolute most combustion engine and then we there.” That meant 2.5-litre four-cylinder parsimonious possible, and then seeing how it could achieve Mazda’s ambitious torque targets while remaining in a fuel efficiency. The best solution? A ue – some 420Nm tion model – on top yActiv objectives of and efficiency. revious model’s ow. e looking for in our y is ‘what is the most efficient internal ngine you can have?’, work backwards from eant making the ylinder as as ow ve ious tight window of turbocharger, something not seen as feasible on its smaller engines.

“For the downsizing approach to really pay off, you have to cross a cylinder-count barrier. So if you take a big (naturally aspirated) four-cylinder and replace it with a (smaller) four-cylinder turbo, it doesn’t pay off,” Coleman says.

“If we’re getting to a scale where we’re getting a really large V6, and we’re able to knock it down to a good-size four cylinder, there’s a huge benefit in dropping those extra cylinders.”

The CX-9’s turbo SkyActiv-G engine makes 169kW, down on the V6’s 204kW, but its 420Nm eclipses the older engine’s 367Nm, and it’s produced at 2000rpm instead the V6’s 4250rpm. Fuel economy figures haven’t been disclosed, but Mazda says the new engine delivers a 20 percent improvement compared to the existing CX-9, which suggests a figure of around 8.8L/100km.

Mazda also had to weigh up the cost of direct fuel-injection, its exhaust-gas recirculation cooling and the expense of the turbo itself. “We could have made a SkyActiv V6, but the efficiceny worked out better with a turbo because of that huge drop in friction, and huge drop in weight,” Coleman says. “It works out a lot better as a turbo four.”