When paired with quattro all-wheel drive, the 4.0 TFSI now accelerates the A8 from 0 to 100 km/h (62.14 mph) in 4.5 seconds. Under partial load, the Audi cylinder on demand (COD) system deactivates four of the eight cylinders.
Cylinder deactivation (ACT)
With conventional wastegated turbochargers or fixed geometry turbochargers (FGT), a turbine flow area cannot be adjusted during operation.
Knocking is abnormal combustion in which the air-fuel mixture ignites prematurely due to exposure to high temperature and pressure, creating an unwanted high-frequency noise. When the compression ratio is increased, the temperature at compression top dead center (TDC) also rises, increasing the probability of knocking.