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Results from two separate emission test programs using a fifteen fuel test matrix in which ten key fuel properties were independently varied have shown that changes in gasoline distillation characteristics, olefin content and Reid vapor pressure (RVP) can produce major changes in total tailpipe exhaust emissions. All other variables examined, including oxygen content and aromatic content of the fuels, did not directly affect the tailpipe output of carbon monoxide, nitrogen oxides, or hydrocarbon emissions. From these results a generalized mathematical model was produced which predicts tailpipe emission changes from key fuel properties. The model was verified in a separate, 13 vehicle study.

In 1985 the U.S. Environmental Protection Agency instituted regulations which have ultimately limited the lead content of leaded gasolines to 0.1 grams of lead per gallon. There is currently very little test work on the potential for exhaust valve seat recession while running an engine with a cast iron head without hardened exhaust valve seats on gasoline at this lead level. Therefore, we have examined valve seat recession from low lead fuels. The test program described here evaluates test conditions and additives which can affect exhaust valve seat recession in mid-1960s vintage heads. Cylinder heads produced after the early 1970s had induction hardened exhaust valve seats and were not susceptible to exhaust valve seat recession. Specifically, tests were run in which lead, air/fuel ratio and engine hardware (valve rotators) were varied and evaluated for contribution to the valve recession process.