Cooper had prepared a chassis, designated T80, to take the Climax FWMW flat-16 1.5 litre engine for 1965 but the engine had suffered development problems and more importantly was no more powerful than the existing FWMV V8. Cooper then repurposed the chassis as a development mule for the MaseratiTipo 9 2.5-litre V12, enlarged to 3 litres. The Maserati engine would be used in Cooper's first purpose-built 3 litre Formula One car, the T81.