A Comparison of Transient Vehicle Performance Using a Fixed Geometry, Wastegated Turbocharger and a Variable Geometry Turbocharger

The use of an exhaust-driven boosting device can significantly improve the performance of a vehicle using a small displacement engine. One of the concerns relative to the performance of vehicles using these devices is “turbo lag,” or the period of time during which no boost is generated. This paper presents the results of designed experiments comparing the performance of a fixed geometry, wastegated turbocharger to a variable geometry turbocharger incorporating a low-loss bearing system. In addition, experimental tests are presented for the naturally aspirated engine in the same vehicle.

The results of the experiments show improvements with the use of pressure boosting and that there are significant differences in the boosting devices tested; specifically, the use of a variable geometry turbocharger demonstrates significant reduction in the length of time required to reach boost and reduced acceleration times for the tests conducted.