Power pumps

  • A turbo is essentially two fans connected by a shaft. One fan, the turbine, is spun by the engine exhaust, powering the other (the compressor), which pressurises the air fed to the engine. The turbo is …efficient because it uses normally wasted exhaust energy. Images by Dan Saelinger.
  • The supercharger – or blower – pumps compressed air into the engine, increasing power. Since it’s belt-driven, like an alternator, the supercharger supplies boost in as little as 250 milliseconds. Images by Dan Saelinger.
Date:1 August 2012 Tags:,

To get both fuel economy and power, car manufacturers are boosting engines with pumps that provide extra kick when needed. Here’s how turbos and superchargers work…

Big engines provide a satisfying surge, but most of the time we’re using only a fraction of an engine’s maximum power. To increase fuel economy, manufacturers are rapidly employing smaller engines – both in displacement and cylinder count. Downsized engines can, however, produce big-motor power with the help of pumps that force more air into the engine. The extra air, combined with fuel, makes a more powerful “boom” when the spark plugs fire, increasing power.

Automotive engine pumps come in two flavours: turbochargers and superchargers. Turbos are currently the defacto small-engine power booster because they efficiently run off the engine’s exhaust. This energy may be “free”, but there’s a slight delay between the time the driver presses the accelerator pedal and when the turbo generates boost (the delay is known as turbo lag). While turbo-makers have reduced the lag with twin-scroll ducts that increase gas velocity, surviving in the over 1 000-degree exhaust requires exotic and expensive materials such as cast stainless steel and Inconel, a nickelchromium alloy.

Superchargers have typically been employed when peak power – not saving fuel – is the ultimate goal. But refinements such as helical rotors and a bypass system for coasting have increased the blower’s efficiency so that several manufacturers are keen to take advantage of the super charger’s relative simplicity and lower cost. Plus, a supercharger offers near instantaneous response, so a downsized, supercharged engine feels punchier in heavier vehicles such as SUVs. Compared with a nonboosted engine of equal power, a smaller “pumped” one is roughly 10 per cent thriftier, which is why the majority of new-car engines will almost certainly be boosted by the end of the decade.

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