In 1961, F1 adopted the new 1.5 L engine regulations, and Walker flirted with the idea of building his own chassis, but retained the Lotus 18 for the season. Moss won the non-championship races at Goodwood in the 2.5 L Intercontinental Formula and Vienna, as well as the Monaco and German Grands Prix. At the 1961 British Grand Prix, Rob Walker Racing became the first team ever to enter a four-wheel drive car for a World Championship Grand Prix, when they entered the Ferguson P99 on behalf of Ferguson Research. Moss later won that season's Oulton Park International Gold Cup race in the same car; to date, this is the only win ever recorded by a four-wheel drive car in a Formula One event.