Exhaust Valve Recession with Low-Lead Gasolines

Effective January 1, 1986, regulations by the U.S. Environmental Protection Agency limited the amount of alkyl lead antiknock additives that could be used in “leaded gasoline” to 0.1 gram per gallon. This has led to considerable concern about the potential for serious wear problems in older engines that were designed to run on leaded fuel. Phillips has completed a study to address this concern and identify limits of potential impact. This paper reports the results of this work.

The subject test program was completed on a late model 302 Ford V8 engine modified to be equivalent to engines built prior to 1971 (primary engines of concern). The reported results show that fuel containing as little as 0.05 gram per gallon lead is sufficient to protect engines operated at low to moderate speeds against excessive wear. However, engines operated at high speeds are shown to need protection over and above that afforded by the use of fuels containing the 0.1 gram per gallon EPA target lead concentration. Engine load is shown to be a less important factor than engine speed in terms of exhaust valve seat wear. Additionally, the potential for unleaded gasoline to drastically reduce all the affected engines' operable life spans is demonstrated. Detailed test procedures and program results are discussed along with recommendations for the owners of the affected engines.