RT-X engine: Diesel or petrol future?

Forced aspiration is the way of the future, but will that be with a petrol or a diesel engine?

RT-X engine: Diesel or petrol future?

I’VE been driving a couple of different variants of the new Suzuki Vitara range this month.

Unfortunately with monocoque construction and no low-range or fully independent suspension this new Vitara isn’t a tough 4x4 like previous Vitaras, but it’s interesting nevertheless thanks to two very impressive engines: one representing the present, and one that looks very much like the way of the future.

The automobile’s rise from curiosity to ubiquity in the last 100 years has come off the back of free enterprise. However, in more recent times that free enterprise has been subject to increasing government influence and control. For example, the fact the vast majority of new 4x4s sold in Australia today are diesel- rather than petrol-powered is a result of political decisions made in Europe in the 1990s.

A broad framework of government policies (vehicle and fuel taxes, etc.) that supported diesel engines as a key strategy in the EU’s push to lower vehicle ‘greenhouse gas’ emissions led to a huge investment and consequent rapid advancement in diesel-engine technology. Car companies quickly transformed the diesel engine from dunger to superstar in just a few years, thanks largely to electronic high-pressure fuel injection systems and sophisticated turbochargers.

The knock-on effect is that modern diesel engines are so good compared to petrol engines that few new 4x4s are now petrol powered – and when a petrol engine is offered it sells in tiny numbers.

Still, while one hand gives, the other takes away. The very Europe that instigated the rise in diesel popularity is now moving in a direction that could see diesels consigned to history – ever-tightening exhaust emission standards risk putting the kybosh on the TDi party.

Australia has moved to line up with exhaust emission standards developed in Europe under the so-called ‘Euro’ standards. These standards address many things, but critical to diesel’s future are particulates (soot) and the various oxides of nitrogen collectively known as NOx.
Right now the car industry is dealing with Euro 5, which targets particulates with mandatory use of a diesel-particulate filter or equivalent technology. From 2018, Euro 6 targets NOx and will need selective catalytic reduction (AdBlue) or equivalent technology. With new engine designs and specific technology, car makers have E5 and E6 covered for diesels.

By around 2020 even tighter proposed standards in Europe and the USA will make the game even tougher for diesels – so much so that many car companies are now saying enough is enough and they won’t be able to build diesels that comply with future regulations.

There is good news, though, and it’s plain to see behind the wheel of this new Vitara and its turbocharged petrol engine. Most telling was driving this turbocharged petrol engine back-to-back with the optional turbocharged diesel, a modern Fiat design backed by a sophisticated six-speed dual-clutch sequential gearbox (GSG) – effectively a contemporary ‘best-practice’ diesel powertrain.

Both engines are fours, the petrol a 1.4-litre and the diesel slightly bigger at 1.6 litres. The diesel claims 88kW at 3750rpm, while the petrol claims 103kW at 5500rpm. As expected the diesel offers far more peak torque, 320Nm against the petrol’s 220Nm.

But there’s a qualifier: the petrol’s 220Nm is delivered over a spread of engine speeds from 1500rpm to 4000rpm; while the diesel’s 320Nm peaks at 1750rpm and declines thereafter. That the petrol engine makes good torque at higher engine speeds than the diesel is why it ends up making more power.

On-road the diesel is grunty, while the petrol is zippy and ultimately quicker. It’s also more refined, smoother and quieter than the diesel. On give-and-take undulating roads the diesel’s DSG holds onto the taller gears better than the petrol’s six-speed torque-convertor auto, but there’s not much, due in part to the torque convertor’s ability to unlock and ‘slip’ – which the diesel’s DSG can’t do.

After more than a week in identical conditions the diesel used a thrifty 5.5L/100km, while the petrol used 6.5L/100km. An excellent result, even if the petrol does ask for 95RON.
If diesels follow the dinosaur there’s much to be said for new-gen petrol turbos, designed for broad torque rather than high power.


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Fraser Stronach

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