Upon his return from South Africa Brown decided to design and build his own car. Working in his bedroom each night until 2:00 am, he designed a 1.5-litre twin-cam, straight-eight engine. Then using the firm's foundry, he made patterns and cast the cylinder block, while using the machine shop to produce the other components. His father put a stop to the work when he caught his son working on the project in company time. Undaunted, Brown constructed a chassis, fitting it with a Sage 2-litre engine, coupled to a Meadows gear box. He called the result the “Daybro”. David Brown & Sons' gear-grinding skills brought him early contacts with Bertelli of Aston Martin for gears and Amherst Villiers for his superchargers. With the consent of Villiers, Brown modified a Vauxhall which then won its class at Shelsley Walsh for three consecutive years. It was said to be capable of more than 140 mph on the sand.