Dear Doctor: I own a BMW 5 Series with the twin-turbo engine and I’ve been extremely pleased with the fuel economy. I’m considering a trade for the Audi A6 with the supercharged engine. Knowing a turbocharger is a “demand” boost, while a supercharger is belt-driven and therefore “full time,” will I still be able to achieve comparable fuel economy? Jim
Dear Jim: The exhaust-gas driven turbocharger does have a slight advantage over the belt-driven supercharger. The use of twin turbochargers is what a lot of manufacturers do with V-6, V-8, V-10 and V-12 engines. Turbochargers use the exhaust gases to spin a small turbine wheel. There is no power robbing from a belt-driven supercharger. A supercharger uses 2 horsepower to build 10 horsepower. Both do make horsepower and we will see smaller twin turbos as the technology advances. I like the turbo vs. supercharger.