LEAD FREE

Until 1973 all new vehicles used gasoline that had tetraethyl lead or some other lead compound as an additive to increase octane rating and reduce knock or detonation . In 1973, almost all new cars required lead-free gasoline ( unleaded gas ). The exhaust valves in older cars were lubricated by the lead, so they were redesigned to accommodate the new gasoline . To offset the detonation problem, the compression ratio was also reduced. Lead-free gasoline was introduced to remove the lead in the exhaust fumes as a health hazard.