Having read about the impacts of leaded fuel on car design when it was introduced in the 1920s, along with efforts in France to ban lead-based paints at the same time, I have wondered what would have happened if European nations had banned leaded fuel before it was introduced there in the late 1920s and 1930s.
There was already divergence between American and European car design at that time, and today I have been thinking about how much greater this divergence would have become if Europe had not allowed the increases in gasoline octane rating permitted by tetraethyl lead.
Would the larger-volume European makes have gradually turned to exclusive use of diesel engines?
Would gas turbine engines have become used in upper crust European makes with fuel octane limited to (say) 75 RON?
How much would banning tetraethyl lead from its invention have affected the growth of European automotive industries for export after the war?