When the VGT is closed it maximizes the use of the energy that is available at low speeds. Closing the VGT accelerates exhaust gas flow across the vanes of the turbine wheel. This allows the turbocharger to behave as a smaller turbocharger. Closing the vanes also increases the exhaust pressure in the exhaust manifold, which aids in pushing exhaust gas into the intake. This is also the position for cold ambient warm-up.