A precisely controlled, stabilized internal combustion engine is used to generate exhaust gas with fixed emission composition (HC, CO, NOx, O2, CO2), and exhaust temperature. A two-way valve in the exhaust duct switches this gas into a catalytic converter initially at room temperature. The transient warmup and steady-state conversion efficiencies are printed out along with strip charts of the exhaust gas concentrations out of the converter, and gas temperature into and out of the converter. The transient response is particularly important since vehicle emission is much higher during the first few minutes of the Environmental Protection Agency (EPA) driving schedule. Thus, this test is effective in predicting EPA performance of the converter on a particular converter test vehicle. Actual experimental results correlate very well. The math model for generating the predicted normalized EPA results has been developed.