In the 1960s, exhaust valve faces and seats were lubricated with tetraethyl lead in gasoline. Beginning in the early 1970s, oil companies began removing lead from automotive fuels to help lower air pollution levels. Automakers began using hardened exhaust valve seats as a response. When rebuilding a vintage Mustang engine, cylinder heads need hardened exhaust valve seats and new valves. Here, JGM cuts the original iron exhaust valve seat in preparation for the steel insert.