Mazda on SKY high

Petrol engines with diesel economy and super economical diesel engines with better than petrol performance. They are the promises of Mazda's next generation SKY powertrains.

Exposed to the media in surprising detail (fully a year before they find their way into local models) at a workshop in Berlin Germany late last week, the new SKY-G petrol and SKY-D turbodiesel (pictured) direct-injection powertrains are Mazda's weapons in its battle against other makers' hybrid and downsized turbo engines.

Unlike the downsized forced induction route favoured by the European brands, Mazda is pursuing 'drastic' improvements in combustion efficiency as its tactic to significantly decrease emissions and boost fuel economy. It says via the new SKY technologies it has achieved class-leading economy and emissions performance while retaining traditional engine capacities.

In introducing its new powerplants, Mazda is claiming 4.2L/100km fuel economy for a diesel-powered version of the next-generation 6 due in 2013. Such economy would place the medium-sized car right at the very pointy end of the most efficient small and light cars on the Australian market.

The first SKY-G and SKY-D engines to be released initially are 2.0 and 2.2 litres respectively. Both are all new. Though there's no official confirmation on a smaller turbodiesel unit yet, don't bet against a 1.6-litre oiler in the medium term. The 2.0-litre SKY-G petrol engine will quickly be joined by 1.3, 1.5 and 2.5-litre variants, the last of which will replace Mazda's V6 engine in markets like the USA.

The 2.0-litre is smaller in bore (83.5mm v 87.5) and longer in stroke (91.2mm v 83.1) than Mazda's current convention unit and features tuned length induction and a motorcycle-style fabricated tube four-into-two-into-one extractor exhaust set up.

The SKY-G power plant also features an improbably high compression ratio of 14:1 when fuelled on the 95RON petrol offered in Europe. In Australia (and Japan) where 91RON is standard it will still use a sky-high 13:1 ratio.

The ability to uses such high ratios is the secret behind the SKY-G's efficiency. In part this is facilitated by better cylinder scavenging via the tuned exhaust system. Cooler, cleaner air in the chamber reduces the chances of pre-ignition (knock) and optimises combustion efficiency.

Mazda has also paid particular attention to reducing friction losses within the powerplant. It claims the SKY-G engine exhibits 15-20 per cent lower internal friction than a conventional engine.

The all-new 2.2-litre diesel shares its bore and stroke dimension with the current generation turbodiesel powerplant but that is about all. In an intriguing counterpoint to its petrol stablemate, the SKY-D's efficiency is centred on a lower compression ratio than conventional diesels -- also around 14:1.

The brainchild of Mazda's combustion guru Mitsuo Hitomi, the SKY-D capitalises on the counterintuitive reality that a lower compression ratio diesel delivers a significantly bigger bang' (higher expansion ratio) for more power and torque and less emissions. The SKY-D therefore already complies with Euro 6 emissions and does not require any exhaust after-treatment to reduce NOX levels -- a bugbear for modern high performance turbodiesels.

Twin sequential turbochargers are featured for absolutely linear torque characteristics -- a characteristic made all the more apparent thanks to the SKY-G's very high (for a diesel) redline of 5200rpm. The turbo hardware is plumbed into the cylinder-head via an integral exhaust manifold.

Mazda claims to have shed several kilograms from both engines. Lower peak combustion pressures mean the diesel engine can use componentry that is closer to petrol engines in size.

In the case of the turbodiesel significant reductions have been made in reciprocating mass. The SKY-D's crank, conrods and pistons are 26, 20 and 25 per cent lighter than current components respectively.

Indeed, weight reduction is an important string to the Mazda SKY philosophy's bow. The carmaker is pursuing aggressive weight reduction targets in both the engine room and chassis of its next generation models. It says the new Mazda6 due in 2013 will be at least 100kg lighter than the current car -- though key dimensions have grown (see separate story).

Matched to new, lighter and more efficient SKY-Drive six-speed automatic and manual transmissions, the SKY powerplants are set to produce hybrid-rivalling fuel economy without sacrificing performance, says Mazda.

The new manual is intended the replicate the shift feel of Mazda's sportscar icon, the MX-5, but it's the SKY-Drive auto's efficiency that is especially noteworthy.

Though in the main a conventional epicyclic automatic transmission, Mazda has paired a conventional but more compact torque converter with a wet multiplate clutch to produce a gearbox that it is more efficient in all types of driving, better in low-speed manoeuvring and shifts faster than a dual-clutch automated manual.

Able to lock-up drive for maximum manual 'feel', and efficiency in all six gears, Mazda also claims the SKY-Drive auto has lower mechanical losses than even the best dry multiplate dual-clutch transmissions. There's none of the launch 'reluctance' DSGs still seem to exhibit either.

Like the new manual six-speeder, two versions of the SKY-Drive autobox have been built to partner the petrol and diesel engines. The gearboxes are rated at 270 and 460Nm respectively.

Though the benefits of the engines and transmission combinations will only be realised fully in the next generation of Mazda models, Mazda claims the 120kW/210Nm 2.0-litre SKY-G petrol engine will return fuel economy of around 6.0L/100km matched to the SKY-Drive autobox in a Mazda3.

The SKY-G is set to provide even more impressive numbers. Despite pumping out 136kW and 420Nm, the turbodiesel will return a combined fuel consumption figure of just 4.2L/100km in both the manual and auto variants of the larger but lighter next generation of the Mazda6, Mazda's worldwide chief of product planning and powertrain development Kiyoshi Fujiwara told the Carsales Network.

Retaining conventional engine capacities may also seem counterintuitive when European brands are building large cars with 1.4-litre engines, but there's method in Mazda's 'madness', stresses both Fujiwara and Hitomi.

Chasing 'perfect' combustion efficiencies first opens the way to later downsizing and turbocharging if necessary, they say. And in the long term Mazda's larger (when compared to downsized engines) capacity engines will better allow the brand to capitalise on the next generation of lean burn technologies for even better economy, emissions and performance.

The same goes for blending Mazda's super-efficient SKY powerplants with hybrid componentry at a later date.

Fujiwara also stresses that Mazda's SKY strategy also eliminates the cost and complexity of the forced induction hardware the likes of BMW and Volkswagen are having to build into their smaller capacity engines.

While the full SKY rollout is to be staged through to around 2015, Australian consumers will get their first taste of a SKY-G powered Mazda toward the end of 2011.

Tipped to arrive in an 'interim' SKY-G update of the Mazda3 late next year, it's a version of the 2.0-litre petrol engine highlighted in Berlin that we'll see.

The current Mazda3 chassis layout makes fitting the new high-efficiency exhaust problematic so the special edition will not get every tweak in the new Mazda armoury. Nonetheless expect a torque boost of around 15 per cent and a corresponding reduction in fuel consumption.

You can also expect the car to be the first conventional auto in its class to get stop-start as the package will almost certainly feature a further developed version of Mazda's iStop system from launch.

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