Why does engine smoke after removing catalytic converter?

Removing the catalytic converter can lead to engine smoke due to several factors. The absence of the converter alters exhaust flow and can cause an increase in back pressure, which may lead to incomplete combustion of fuel. This inefficiency can result in unburned fuel entering the exhaust system, producing smoke. Additionally, the removal can expose other components to higher temperatures, potentially causing oil leaks or burning oil, which also contributes to smoke.