4. Honda Civic CVCC (1975)
The 1975 Honda Civic CVCC introduced the Compound Vortex Controlled Combustion engine, enabling the vehicle to meet stringent emissions standards without a catalytic converter. This innovation allowed the Civic to run on both leaded and unleaded fuel, offering consumers flexibility and cost savings. Despite its significance, the Civic CVCC’s role in the emissions revolution is often overshadowed by more prominent models. [Source: Car and Driver]