How they work and why they matter
Automakers pour vast resources into designing engines that make more power while using less fuel – and they have their work cut out for them. Drivers demand engines that are strong and sporty, but also efficient and economical. Is it possible to have both? Adding a turbocharger or supercharger can provide the best of both worlds. They’re a common way to make a smaller engine more powerful while maintaining fuel efficiency.
The nuts and bolts
Turbochargers and superchargers (also known as forced induction) are essentially compressors that work to compress the air-fuel mixture that ignites inside the engine. By compressing this mix, it’s possible to squeeze more air into the engine cylinders, and more fuel along with it. The increased level of oxygen helps the fuel burn more completely, resulting in combustion that pushes the piston down with greater force, creating more power without increasing the size of the engine.
The basic concepts of forced induction are similar, but the way turbochargers and superchargers work is different. Turbochargers are made up of two fan-shaped turbines, each contained in its own housing. The turbines are connected by a shaft so they spin together. Ducting puts one turbine in the path of the engine’s exhaust, while the other faces fresh outside air. As exhaust gases flow out of the engine and through the housing, it causes one turbine to spin. Simultaneously, the other turbine sucks in and compresses fresh air as it moves toward the engine. When it reaches the cylinders a greater amount of fuel is injected to match. As the compressed mixture burns and exits the exhaust, it passes over the turbine again, driving it even faster and increasing the air pressure — and power — as engine RPMs rise.
While turbochargers are driven by exhaust, superchargers are powered directly by the engine. A pulley connected to the engine’s crankshaft spins screw-, lobe-, or turbine-shaped impellers inside the supercharger housing. The impellers work to suck in and compress outside air before forcing it into the engine, again allowing a higher concentration of fuel to enter the cylinders, and for more power to be generated.
Worth the hype, or overboosted?
But if turbochargers and superchargers are so great, why don’t all engines have them?
Anyone who’s driven a turbocharged car from the late ‘80s will complain of turbo lag, a sometimes unpredictable surge of power when exhaust gases suddenly reach high enough pressure to spin the turbines (to be fair, modern turbocharged engines have all but done away with turbo lag). Since superchargers are powered by the engine, they sap some of its output and can actually cause a net loss of efficiency (although any supercharged engine from recent decades won’t have this problem). In either case, they add weight and complexity to an engine, which can compromise costs, reliability, and ease of repair.
That being said, forced induction is extremely popular in today’s automotive industry, and nearly every automaker offers turbocharged or supercharged engines. BMW’s entire new car lineup is turbocharged, and Volvo builds an engine that’s both turbocharged and supercharged. It’s a proven way to give drivers the power they want while maintaining the fuel efficiency they need. If you’ve never driven a turbocharged or supercharged engine, try one — you’ll probably like it.