Small engines and big performance. We take a look at the role of the turbocharger in the world of rallying.

A mainstay of Subaru’s model lineup, the turbocharger in its simplest form works by forcing more air into the combustion chamber. Put simply this causes the ECU (engine control unit) to react by injecting more fuel, which with more air means a bigger bang, and more power.

But how does the turbo do this? It works by compressing the air before it enters the combustion chamber, forcing more into the engine. As the exhaust gasses leave the engine, they pass through the turbo and spin up the exhaust turbine.

This turbine drives a connecting shaft which spins a compressor wheel. The compressor wheel sucks in air through the air intake at the top of the turbo, and compresses it within the compressor housing, increasing the speed at which the air enters the intake manifold.

As you probably know, turbo charging technology plays a crucial role in any World Rally Car, by allowing relatively small engines to produce substantial power. For example; the WRC2008 produces around two and a half times the amount of torque of a roadgoing Impreza STI. This means that, in spite of the power output of Subaru’s two-litre boxer engine being capped at 300bhp by FIA regulations, the latest rally Impreza is still able to accelerate to 60mph from standstill in under three seconds even on gravel.

To put all this into perspective, a performance road car turbo produces around 20psi (1.3bar) of boost pressure, and a standard turbo between 10 - 15psi (around 0.8bar). By contrast, the turbo on the Impreza WRC2008 produces up to a monstrous 60psi (4bar) of boost, and this is where the performance comes from.

Whilst incredibly impressive, it helps to bear in mind that the engine alone is worth around three times the cost of a new Subaru Impreza WRX STI, and the cost of the turbo itself is more than enough to buy yourself a Subaru Justy!

But don’t go raiding your bank just yet; even if you are willing to spend the cost of a small hatchback on a single turbo, they are supplied specially to the Subaru World Rally team by Japanese manufacturer IHI. Operating at a temperature of 1000 degrees Celsius, they would also readily melt most of your engine bay, battery, fuse box and all!

Luke Thomson for swrt.com