The majority of our TDI engines are turbocharged using variable turbine geometry to offer an almost constant boost pressure across the widest rev range.
Variable turbine geometry continually adjusts output to ensure all exhaust gas energy is used to regulate boost pressure. Adjustable vanes maintain level boost pressure across a wide control range. Where gas pressure falls at low speed, or rises at high speed, the automatic vane adjustment increases or decreases the supply line cross-section. This variable geometry turbocharger is particularly efficient in reducing turbo lag at partial load - increasing power, improving response and helping reduce emissions.

Article source: www.volkswagen.co.uk