Although there was some activity in the intervening years, it was not until 1987 that Mercedes-Benz returned to front line competition, returning to Le Mans, Deutsche Tourenwagen Meisterschaft (DTM), and Formula One with Sauber. The 1990s saw Mercedes-Benz partner with British engine builder Ilmor (now Mercedes-Benz High Performance Engines), and campaign IndyCars under the USAC/CART rules, eventually winning the 1994 Indianapolis 500 and 1994 CART IndyCar World Series Championship with Al Unser Jr. at the wheel. The 1990s also saw the return of Mercedes-Benz to GT racing with the Mercedes-Benz CLK GTR, which took the company to two titles in FIA's GT1 class.