Part 1 - Variable nozzle turbines (VNT) were supposed to be the killer turbo technology - the wastegateless design able to be matched to engines to give excellent response throughout the rev range. And, while they have been adopted in huge numbers in diesel engine applications, problems associated with the high exhaust gas temperatures of petrol engines have continued to prevent their more widespread use in passenger cars.

 Part2 - No matter how well it is matched to an engine, a turbocharger still has poor low-load performance. This is because the performance of the compressor (the part of the turbo that pumps air into the engine) is dependent on its speed of rotation. Since it is connected straight to the turbine, before the compressor can turn quickly enough to move significant amounts of air into the engine, there needs to be sufficient exhaust gas flow to whiz the turbine around.