Turbochargers: Brutal power, green promise

Porsche has long valued the efficiency of turbocharging - and created an icon in the process. Photo / Supplied

James Bond's creator, Ian Fleming, had the enviable luxury of free choice over his selection of Bond's companions and cars.

So while Pussy Galore, Plenty O'Toole and Honey Ryder graced his arm, Bond's garage housed half a dozen Aston Martins, various Rolls-Royces, a brace of Lotus Esprits and a Saab 900. Now, the Saab was a nice car, but that is pretty exotic company it's keeping. Why would Bond choose a marque more commonly favoured by headmasters and country GPs?

The clue is in the 1981 publication date of Licence Renewed, in which Bond first drives this car. Saab had recently released a radical extension to its range, the Saab 900 Turbo, and it was that five-letter addition to the name that excited the motoring world.

Bond called his car the Silver Beast, which was appropriate given that the power delivery of the early models was so brutal a lot of them ended up in ditches.

Adding "Turbo" to a car's name has become shorthand for saying it is the macho, performance model. Yet although the word is dropped casually into conversations in the pub, most people have at best a sketchy idea of what a turbo does or how it works.

If you have a degree in automotive engineering or a subscription to Car Mechanics Magazine, skip the following paragraph.

Normal internal-combustion engines use the suction created by the down stroke of the pistons to suck air into the cylinders, and if this air is mixed in the correct ratio with petrol, it will ignite efficiently, creating the engine's power. The more petrol ignited on each stroke, the greater the engine's power, but this is limited by the amount of air that can be sucked in and mixed with it. Back in 1905, a Swiss engineer, Dr Alfred Buchi, worked out that if the air could be compressed, a greater volume of air could be pushed into the cylinder, mixed with more petrol, for a bigger "explosion" and therefore a more powerful engine. The turbo is simply the device that compresses the air and forces it into the cylinders - but it needs power to drive it.

Buchi's stroke of genius was to realise that in the same way you can use wind to drive a wind-powered generator and create electricity, you can use an engine's exhaust gases to spin the turbocharger and create pressure. So, a free lunch then? Well, almost. The reason why Bond's Saab Turbo was called the Silver Beast was that, like all turbocharged engines of the era, it suffered from turbo-lag. When the driver wanted more power, he planted his right foot and the increase in exhaust gases made the turbo speed up - but in its own sweet time, and only after its blades had overcome their inertia.

Sometimes the lag, or gap between planting the foot and getting the shove in the back, could be seconds, and a lot could have happened in that time. The bigger the turbo, the bigger the turbo boost, but also the greater the inertia and turbo lag. Drivers of cars with big turbos, such as the Saab 900 Turbo and the Porsche 911 Turbo, worked out that you could try to overcome this lag by anticipating it and flooring the throttle pedal before the acceleration was needed, but getting that wrong could mean a spectacularly quick trip into the trees.

Despite this problem, the power gains to be had from turbocharging were just too big to be ignored. When turbos were fitted to Formula One cars in the 1980s, the extra power was so great that if your team used a turbo, your engine capacity was limited to 1.5 litres instead of 3 litres. In 1988, the McLaren Honda team won 15 out of 16 races with a turbocharged engine just half the capacity of many of its rivals.

Engineers worldwide struggled to harvest the turbo's power without its lag. Saab's route was to use a much smaller and freer-spinning turbo that gave less power gain but virtually eliminated lag. Others, including Maserati with its Biturbo, used two small turbos in parallel to gain the same power increases as a large turbo. Of course, this was all back in the days before it cost $100 to fill up the tank with fuel. Early production cars fitted with turbos could be frighteningly thirsty when driven hard.

Legislation, regard for the environment and consumer reaction to fuel prices might have consigned the turbo to history. But a turbocharged engine is an efficient engine, and with increased efficiency comes the potential for increased economy.

In recent years, manufacturers have been hard at work to develop that potential. Initially, the greatest economies came through turbocharging diesel engines, offering the high performance formerly associated with petrol, yet retaining diesel economy. Some manufacturers have managed to pull off the performance-plus-economy trick with petrol engines, too. VW's 1.4-litre twincharger engine uses an engine-driven supercharger to get over the lag problem, with a turbo that takes over at higher revs to deliver a free power boost. The economy levels that combination delivered won it an award for being the best green engine in 2009, even beating the latest hybrids.

Perhaps the biggest vote for turbos comes from F1. Its recently released engine specifications for the 2013 season will change the current 2.4-litre V8 to a turbocharged 1.6-litre four cylinder. F1 has a healthy record of technology refinements that filter through to mainstream production cars, and there is no reason that development work on turbos will be any different.

- The Independent