text: The contract stipulated that a four-cylinder Ford-based F2 engine would be developed as proof of concept ( see the FVA above ) and that a pure Cosworth V8 would be built based on this .
simplified: The contract told Duckworth to build a four-cylinder Ford-based F2 engine to prove it would work ( see the FVA above ) . After that , a pure Cosworth V8 would be built .