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Forced induction

autos Updated: Aug 27, 2009 11:22 IST
Grease Monkey

The title could possibly mean unwilling college freshmen sitting through a boring orientation ceremony - but in the automotive world, nothing excites an enthusiast so much as the words 'forced induction'.

You've seen the word 'turbo' used often enough to know that when it is mentioned, it means something fast - but it could also mean efficiency. Which is why manufacturers have been putting it in everything, right from high-performance cars to tractor-trailers - even the Indica Turbo has one, as does the Swift diesel, Octavia RS and the Volvo B7R bus. The Bugatti Veyron has four! Here's how they work.

Turbochargers and superchargers do essentially the same thing: they squeeze more air into the available space in the engine's cylinders, in much the same way commuters on the Western Railway squeeze into every available crevice in (and sometimes, on) a train during rush hour. Consequently, both the engine and the train manage to get maximum bang for their buck.

Fuel needs ambient oxygen to combust and produce power, but there's a limit to how much fuel you can put in - if there's too much fuel, it will go unburned, simply because there won't be any oxygen to burn it with.

Introducing more air means there is more oxygen available for combustion, and the end result is small displacement, big power. This will explain why the Nissan GT-R's six-cylinder, 3.8-litre engine produces 475bhp, and the Mercedes-Benz C63 AMG's 6.2-litre V8 produces 'only' 460bhp - the GT-R possesses two turbos to help things along.

Exhaust gases help turn a turbine in a turbocharger, which then compresses air which is on its way to the engine. Since the exhaust gases would otherwise make an exit unused, this makes turbos more efficient than superchargers. 'Blowers' run off the engine's crankshaft, sapping the engine of a little power. However, turbos tend to 'switch on' at a particular engine speed, and the sudden rush of power can make things hairy if the driver isn't expecting it.

If you floor the throttle in an Indica turbodiesel or Accent CRDi at a low engine speed, you'll feel a rush of power at a particular engine speed - this is the turbo getting into action. Superchargers provide a linear increase in power, since they run in direct proportion to the engine's speed and are therefore easier to live with in day-to-day life.

The traditional solution for more power has been adding more displacement or cylinders -mostly both - but a recent trend among car manufacturers has been to downsize the number of cylinders and cubic capacity on engines, and install forced induction. This makes the engines more efficient, since there are fewer moving parts (less moving mass and friction) and not much complexity. Reliability of such engines used to be suspect, but today's high-quality materials have laid that doubt to rest. More kpl and power at a single go!

The argument of whether a turbo or supercharger is better has been raging for a long time, and there doesn't seem to be a definitive answer. There will always be those who will prefer either. Maybe we'll all switch to engines like Volkswagen's TSI range, which run both a supercharger and turbocharger on the same engine for the best of both worlds!

If you have questions or comments for Grease Monkey you can email him at with Auto Tech 101 in the subject line