Fitted in a Penske-Mercedes PC 23, the 500 I IndyCar engine powered Al Unser Jr. to victory in the Indianapolis 500 in May 1994. A change in the regulations meant that this was the only opportunity this high-performance power unit, which was developed in just ten months, had to prove its mettle in race action. Mercedes-Benz had exploited a loophole in the regulations with the engine’s conventional side-valve design.