affectionately as the "Doorstop." In a veiled effort to curtail the turbine's power output, USAC had imposed revised regulations regarding the maximum annulus inlet (reduced from 23.999 in² to 15.999 in²). Another rule change dictated that cars were required to conduct three mandatory pit stops, up from two that were required from 1965 to 1967. Mike Spence was fatally injured after a crash in turn one on May 7. A tire broke off his Lotus "Wedge" Turbine and struck him in the head. He died of his injuries a few hours after the accident after being taken to the hospital. Spence's death came one month after Jim Clark's at Hockenheim; Clark was scheduled to drive one of the Lotus Wedge Turbines at Indy. Pole Day Time trials – Saturday May 18 Graham Hill, the 1966 winner in the #70 STP Turbine, was first to qualify and set a new qualifying record. Later, his STP Lotus 56 teammate Joe Leonard in #60 won the pole position with a four-lap average speed of . Second Day time trials – Sunday May 19 Rain kept cars off the track most of the day. Only two cars were able to make an attempt, and only one was run to completion. At 5:45 p.m., the track was finally opened for qualifications, and Jochen Rindt was the lone qualifier at , while Denny Hulme waved off as the 6 o'clock gun went off. At the conclusion of the first weekend of time trials, the field was filled to 16 cars. Third Day time trials – Saturday May 25 Sixteen cars made a total of 24 attempts, and filled the field to 26 cars. High winds kept some cars off the track, and speeds were down from the previous weekend. Many cars waved off, and Mel Kenyon, at , was the fastest of the day. After qualifying, Ronnie Bucknum's car was disqualified for being underweight. Fourth day time trials – Sunday May 26 With the field filled to 25 cars (eight spots open), rain kept the cars off the track until late in the day. The final scheduled day of time trials ("Bump Day") was almost a complete wash out. The traditional 6 o'clock closing time came and went, and the track was still wet. Track crews continued to work, and the track opened for practice at 6:55 p.m. After the mandatory 30-minute practice session, the track