As proposed by Issigonis, the engine itself was also radical, being a water-cooled flat-four unit. One of Miles Thomas's few restrictions on the Mosquito project was that it had to have an engine that would not fall afoul of the British horsepower tax, which taxed cars under a formula relating to their engine cylinder bore. At the same time, Thomas wanted the car to appeal to the all-important export markets, which had no such restrictions, and generally favoured larger-engined cars. Issigonis' solution was the flat-four engine, which could easily be produced in two versions – a narrow-bore 800-cc version for the British market and a wide-bore 1100-cc version for export. Both versions would use identical parts, except for the actual cylinder blocks (which could still be produced on the same machinery) and the pistons. The flat-four layout reduced the overall length of the engine, further increasing potential cabin space, and reduced the car's centre of gravity for improved handling.