VNT turbos

VNT turbos 2018-02-05T00:40:04+00:00

Since the late 1990s many diesel cars have been fitted with a turbocharger using a Variable Geometry Turbine or Variable Nozzle Turbine. These turbochargers are very effective in minimising the effects of turbo lag, resulting in a more responsive throttle especially at low engine speed and much improved torque.

These systems work by changing the speed and direction of the exhaust gases onto the turbine wheel. The most common of these systems is Garrett’s VNT ® mechanism which incorporates a ring of small movable vanes around the turbine wheel. At low engine speed, the vanes are in the “closed” position narrowing the gap between them which accelerates the exhaust gas onto the turbine wheel. At high engine speed the vanes open up slowing the exhaust gases, which prevents the turbocharger over-boosting. In most cases this level of control negates the need for a conventional wastegate.

Variable-vane turbo cutaway
TT VNT turbo cutaway

Despite these benefits, such turbochargers can be prone to problems. The vane mechanism is easily affected by carbon build-up, which can cause the mechanism to jam. This can occur quite quickly if the vehicle is used predominantly for short journeys where the engine is not allowed to get up to full operating temperature. The mechanism may jam in either the fully open or fully closed position resulting in no boost or too much boost from the turbo. If the turbo over-boosts there is a real danger that it’s internal components will be damaged, resulting in the need for a complete replacement unit. In many cases, the computer controlling the engine will sense a fault and will severely limit the engine’s performance in what is called a “limp-home” mode to prevent any further damage. Low boost may also cause black smoke under acceleration. The problem may clear itself by cycling the ignition switch, but it is very likely that the problem will recur.

Previously,  the VNT mechanisms could only be calibrated by the original manufacturer. However, Turbo Technics have developed equipment to reproduce the factory calibration (see VTR100 and VTR200) and this is no longer a barrier to remanufacture.

If you have experienced these symptoms and have been told that you need a brand new turbocharger, then give us a call. Because of the potential savings, you may be pleased you did. Please contact our Sales Team to discuss your requirements in more detail.