A boost in sales

BTN Turbo explains how the market is growing as manufacturers realise their efficiency

Published:  06 March, 2015

BTN Turbo

The reason is primarily economy. A smaller turbocharged petrol or diesel engine is 20 to 40% more economical than a larger naturally aspirated engine. So manufacturers are increasingly producing models with three cylinder turbocharged engines of around one litre, which are as powerful as a non-turbo 1.6-litre.

These smaller engines are naturally lighter than their larger predecessors, reducing overall vehicle weight, further improving economy and reducing emissions. It's not just the supermini class that benefits from these compact power units; their efficiency means they provide sufficient performance for C-segment cars, such as the Ford Focus, with its EcoBoost range of engines.

Highly successful

Peugeot and Vauxhall have their own highly economical downsized engines, with the PureTech e-THP and ECOTEC units respectively. Peugeot's 1.2 litre, three cylinder PureTech e-THP fitted to its big selling 308, uses a turbo spinning at up to 240,000rpm (4,000 revolutions per second) to produce 130bhp. Vauxhall's ECOTEC takes technology originally used in 2.0 and 2.5 litre engines, and has shrunk to the all-alloy 1.0 litre direct injection turbo used in their urban-chic ADAM.

It's the turbocharger that has made these impressive gains in economy and output possible. From simple wastegate turbos, the turbocharger has evolved to become ever more sophisticated.

Currently the largest category of turbos produced for passenger cars is the variable turbine type, managed by sophisticated integrated ECUs. These have overcome the problem of insufficient boost at low revs and too much at high revs. Using either moving vanes or nozzles, the variable turbine turbo provides an optimised level of boost for the combustion and load characteristics across the engine's rev range.

Latest generation

At the same time, turbo flow technology has been progressing too, with innovations such as twin scroll turbochargers, and two and three-stage turbocharging.

Innovations such as these make the turbocharger an integral part of future engine developments - and not just for petrol and diesel engines. Advanced turbos are already powering fuel cell, natural gas and ethanol concepts - though it might be a while before you see these coming into your workshop!

Twin scroll turbos

The benefits of this can be seen, for example, in the Mercedes-Benz A45 AMG. Despite being only two litres, with its BorgWarner twin-scroll turbo the engine produces just over 350bhp, which is an incredible 180bhp per litre - yet it can still return 34mpg.

Two- and three-stage turbocharging

Again, the result is greater efficiency that releases more power from a smaller engine. As far back as 2011, Garrett developed a two-stage turbocharger for the Audi A7, which despite having an engine 30% smaller than the previous model, actually produced 35% more power and 10% better economy.

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