The rest of the running gear – engine, radiator, gearbox, differential, complete brake system (less the ABS) and some suspension components – is all taken from a BMW 325i.
The Coopers try to buy a complete donor vehicle and preferably one that is running so that any problems can be detected before the vehicle is stripped. Donor vehicles are becoming scarce, though, and premium prices are being asked. As 325i diffs and gearboxes never give trouble, only the oil seals are changed, but with the engine no chances are taken.
Each six-cylinder motor is stripped right down and completely overhauled, receiving new oil and water pumps, pistons, rings and bearings. The 325i’s engine management system is preferred because of its obvious compatibility benefits – the choice staying standard, altering the mapping or fitting an alternative ECU is left to the customer.
The most recent car to be built was fitted with a SPI-tronics ECU. Left over bits from the 325i gradually get sold through the second-hand spares and scrapyard side of the Cooper’s multi-faceted business.