Under EPA contract, the Holley Carburetor Division of Colt Industries developed an application of the Dresser Sonic Carburetor design for evaluation by EPA. The Holley Sonic Carburetor was tested for emissions and fuel economy in a 1975 California model Dodge Dart with a 3.7 litre (225 cu. in.) six cylinder engine. The test results were compared to those of the same vehicle in baseline condition (production carburetor and emission control system). Factors such as the air/fuel ratio, idle enrichment, and air injection were varied to optimize the emissions. After an optimum setting was found, the emissions were still generally higher than the same vehicle in baseline condition. Addition of a three way catalyst reduced NOx below baseline, but HC, fuel consumption, and especially CO values were still greater than baseline.