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.