Traditional American luxury automaker Cadillac, best known for soft rides, posh interiors and gray-haired buyers, on Tuesday said it will compete in the grueling 24-hour Le Mans auto race in June 2000. Cadillac officials, who disclosed their plans at the Geneva International Motor Show, said they will use a 4.0 litre version of their technologically advanced Northstar V8 engine to power the Cadillac Northstar Le Mans Prototype. Meantime, American automakers mixed environmentally friendly technologies with their latest sporty offerings at the show on Tuesday.