This paper reports on an exploratory automotive test which was undertaken in the NASA Langley Research Center 14 by 22 wind tunnel in the Fall of 2003. The test was collaboration between Old Dominion University, who supplied the automotive balance, NASA, who provided wind tunnel time, and Penske Racing South, who provided an instrumented test vehicle. The test generated a rather unique data set, encompassing whole body forces, surface pressures, and floor boundary layer profiles, measured on the same test article, with both an open jet and closed jet test section, utilizing the variable configuration of the 14 by 22. The nominal test velocity was 60 m/s, the nominal blockage was 7.4%, and the yaw angle ranged from −6 to +6 degrees. Results indicate substantial interference effects, as expected, with around 19% higher drag (uncorrected) in the closed configuration, relative to open. The corresponding front and rear downforce values were 14% and 13% higher respectively. A simple blockage correction to dynamic pressure is therefore not sufficient to collapse the two data sets. Detailed analysis of surface pressures and boundary layer profiles provides some insight into the reasons for this discrepancy. To support the analysis, boundary interference assessments are being made, using panel methods. In the open jet case, the current method properly accounts for the effects of jet distortion. It is concluded that relatively sophisticated on-line interference assessment techniques should be employed in tests of this type. The paper reviews both uncorrected and corrected data, the interference assessments, and explores the reasons for the inadequacy of classical blockage corrections.