Engine Intel: How Turbos and Superchargers Work

June 21, 2012 3:00 PM

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, automakers 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 horsepower.

Automotive engine pumps come in two flavors: turbochargers and superchargers. Turbos are currently the de facto 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 gas 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 2000 F exhaust requires exotic and expensive materials like cast stainless steel and Inconel, a nickel?chromium alloy.

Superchargers have typically been employed when peak power?not saving fuel?is the ultimate goal (see the Corvette ZR1). But refinements like helical rotors and a bypass system for coasting have increased the blower's efficiency so that several automakers are keen to take advantage of the supercharger's relative simplicity and lower cost. Plus, a supercharger offers near instantaneous response, so a downsized, supercharged engine feels punchier in heavier vehicles like SUVs. Compared with a nonboosted engine of equal power, a smaller "pumped" one is roughly 10 percent 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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