Power drives for economy

…..a vehicle now has to look good, go well and have a label on the windscreen showing it runs on the smell of an oily rag.

The price of fuel and the focus on greenhouse gas emissions – in Australia new vehicles must display their CO2 emissions on a sticker on the passenger’s side of the windscreen – is directly translating into more fuel-efficient cars as manufacturers align with public perception and government policy.

Even supercar makers such as Lamborghini aren’t immune from the hype. The wild child of the VW Group is actually touting the fact its outrageous new Aventador uses 20 per cent less fuel than the outgoing V12 engine.

It’s worth bragging about, but having a supercar maker promote fuel consumption highlights the attention being spent on improving efficiency in every car, from the Suzuki Alto to the Mercedes-Benz S-Class.

At a basic level, car makers fit low rolling-resistance tyres to improve economy, and replace the spare tyre with run-flats or a puncture repair kit. Not having a fifth wheel in the car is worth up to 25kg in weight loss, along with added boot space.

At the next level of investment, alloy panels, such as those announced on the next-generation Holden Commodore and already applied to prestige European cars, are used, typically in such areas as the bonnet, doors and roof. Holden claims that improvements to the Commodore’s aerodynamics and the lighter panels will cut fuel costs by 7 per cent.

The heart of a car is still the engine and transmissions, and that’s where most car makers have invested their research dollars. The consensus is the internal combustion engine can be made up to 30 per cent more efficient. Volkswagen and Toyota already sell cars that use less than four litres over 100km.

The first example of the latest petrol engines from Mazda will come in the form of a 1.3-litre direct-injection petrol engine known as "SkyActiv-G". It is paired with a continuously variable transmission and stop/start technology to return official Japanese fuel consumption figures of 3.3L/100km.

The principles behind the SkyActiv-G range of petrol engines are high compression ratios – 14:1 in the case of the 1.3-litre engine – multi-hole fuel injectors to maximise the fuel-injection combustion process, and piston cavities that are shaped to maximise volumetric efficiency.

Mazda claims a 30 per cent drop in mechanical friction over a conventional engine, due to a narrower crankshaft (which means less rotational mass) and low-tension piston rings that also reduce oil consumption.

Despite the fuel-efficient focus, the engine still produces 62kW/112Nm. Those numbers stack up well against the 76kW/135Nm in the 1.5-litre engine fitted to the existing Mazda2. But it’s the fuel economy that’s the clincher – 3.3 litres against 6.8 litres over 100km.

It’s a similar story on the Kia stand where the five-door Rio hatchback runs the latest engine in the South Korean line-up. The 1.6-litre engine uses direct injection and a stop/start system to return 7.8 litres over 100km, but produces a class-leading 100kW and 164Nm.

On the diesel front, the Ford Fiesta and VW Golf lead the way in terms of driveability and fuel use. They are both fun-to-drive vehicles that give little away to their more powerful petrol siblings.

In the prestige market, Audi, BMW and Mercedes-Benz make diesels that sound and go like petrols but use fuel at about 7.0L/100km. They’re luxury cars with such hi-tech tricks as closing the grille at speed to improve the wind flow over the car, and exhaust system emissions that are comparable to petrol cars. All three have or will soon launch hybrid models in their premium range to join Lexus, which has long held the hybrid moral high ground.