A new test procedure has been devised which provides an accurate, low cost method for studying the effect of exhaust tailpipe configuration on the smoke pattern behind an automobile.In this experiment motion picture records were made of the pattern and behavior of smoke laden engine exhaust behind a typical sedan automobile. These were compared with similar photographs obtained with smoke discharged from the dummy exhaust system of a 3/8 size model of the car in a carefully controlled wind tunnel test. A uniformly excellent geometrical similarity was found to exist between model and full scale test results that held throughout the variety of tailpipe configuration and operation mode combinations tested in the investigation.The results show that wind tunnel tests with the model are technically equivalent to the performance of the actual vehicle. Therefore, wind tunnel tests on models can be used to facilitate the design of exhaust system configurations that minimize or eliminate undesirable exhaust behavior characteristics. This is an extremely significant result because such models are, or can be, available far in advance of driveable prototype vehicles. It is technically possible, therefore, to determine undesirable exhaust flow behavior and devise possible solutions before the car design reaches the prototype development phase.A description is given of the smoke generating and photographic equipment used with the full size vehicle and with its 3/8 scale model.