1987: Mario dominated the 1987 event, and in fact, the entire month of May. He won the pole position, the pit stop contest, and led the daily practice speed chart nearly every day he took practice laps. Driving the new Ilmor Chevy Indy V-8, He led 170 of the first 177 laps, giving up the lead only during pit stop sequences. He had such a big lead that he backed off, but the reduced revs created a harmonic imbalance in the engine. A valve spring broke with only 23 laps to go, and the car coasted to a stop. It was considered one of his most shocking defeats. As a cruel ironic side note here, Roberto Guerrero inherited the lead after Mario went out, drove for Andy Granatelli's son Vince in an STP sponsored car, his final pitstop had problems with results of him finishing 2nd to Al Unser, Sr. whose car owner was Roger Penske.