In the most basic technical sense, a turbo is used to enhance the volumetric efficiency of an internal-combustion engine. To you and me, that means more power from the same engine. To the manufacturer, it means an easy way to add a performance vehicle to their line-up without designing a bigger or more powerful engine. Imagine a diesel engine that develops 60 bhp in normally aspirated (breathing atmospheric air as it is) mode, but churns out 90 bhp when turbo-charged? Thats the kind of difference turbo-charging can make to a vehicles power. The principle on which this works is simple. Every internal combustion engine produces exhaust gases; in a turbo-charged engine, the same exhaust is used to propel a turbine (that, incidentally, is where the word turbo is derived from). The turbine blades spin faster as the flow of exhaust gases increases with engine speed. The turbine in turn powers a compressor that compresses the air and sends it through an air cleaner before feeding the inlet manifolds. So a richer air-fuel mixture enters the cylinder heads, resulting in a larger explosion and more power without any increase whatsoever in the engine size. There is a complication, of course, or wed be looking at the perfect energy-friendly machine. Exhaust gases are very hot compared to the atmospheric air, so most turbo-charged engines have to use an inter-cooler that cools the air. The cooled, but pressurised (denser) air is fed to the engine. This is also called the charged air in-take, done with the help of a turbo-charger unit. So the next time you see a Mitsubishi Pajero with stickers on either side proclaiming that it is a 2500CC Twin turbo-intercooler, you will know that to increase the performance of the 2500CC engine, Mitsubishi has employed the services of two turbo chargers aided by an inter-cooler.
Turbo lore, compiled by avid fans of the technique and its results, points to Saab as the great god of Turbo. When Saab first introduced the 900 with its turbo-charged engine, it became an immediate cult. People who drove regular sports cars and convertibles screeched to a halt and took a second look at Saab 900. First, the car looked different, and then it had its quirks. It was the quirks that made the first ever turbo-charged production car famous. The Saab 900 would start off and drive like any normal, non-spin doctored vehicle while the turbo-charger took its own sweet time to spin at a fast enough speed to produce a noticeable difference in power a phase promptly dubbed turbo-lag. As the car built up speed, the exhaust pressure built up too. And suddenly the turbo fans would find themselves spinning and rolling out a liberal surge of power.
This was a quirk with enough in the way of dramatic results to make driving a turbo an interesting affair. The Saab 900 also benefited from superb suspension and impeccable sports car manners, without compromising on the comforts of a modern-day coupe. A legend was born and soon people started seeing more turbos on the road as every performance car maker in the world got into the act.
In the mid-eighties, even the motorcycle manufacturers tried to cash in on the craze with turbo-charged motorcycles, but this was a short-lived boom. It faded away with the introduction of more comprehensive methods of adding power to the pickup such as through multi-valve engines to enhance the power of the internal combustion units. The prerequisite to turbo charging was fuel injection, and the diesel engines had an advantage here since all diesels had a form of fuel injection.
Multi-valve engines, roughly, are ones that have more than one inlet and one outlet valve per cylinder. They improved the performance of petrol engines considerably and were a very reliable way of beefing up power. But the diesels continued to be sluggish. Trucks had benefited from turbo power and soon the trend spread to those passenger vehicles powered by diesel engines. Turbo-charging made diesel engines more desirable than ever (as a general rule, diesel engines are 20 to 30 per cent more fuel efficient). Even those who wouldnt be seen near a standard diesel-powered car because of the lack of performance started buying the same cars precisely for their performance. Technology has taken a few strides forward since the early days of turbo, and now most major manufacturers use turbo-charged diesel engines only either in sports-utility vehicles or in diesel-powered passenger car variants.
But even today, the word turbo translates anywhere in the world into performance. To an enthusiast, it translates into much more than that its a cast-iron guarantee of adrenaline rushes when its written across the flanks of any automobile.
