What is it?
Twenty years ago, the notion that a diesel-powered car could ever seriously challenge an acknowledged, upper-echelon performance car on track would have been ridiculous.
Like its more powerful stablemate, the A6 TDI quattro concept is equipped with a new electric compressor technology designed to banish turbo lag once and for all. This additional compressor takes the form of a small supercharger, which is driven by a 7kW, 48-volt electric motor.
Diesel engines suffer lag badly compared to petrol because their great efficiency results in cooler exhaust gasses. There's consequently less energy available to spin a turbo, especially at lower revs.
Unlike the RS5 TDI concept, the A6 TDI concept is equipped with the new 3.0 TDI single-turbo engine from the standard A6. The electric compressor is installed downstream from the intercooler in series with the conventional turbocharger system.
At low revs the electric compressor fires up and reaches maximum speed in just 250 milliseconds, plugging the torque gap that causes lag.