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Chevrolet explains issue that derailed several Indy 500 qualifying runs

There were concerns early on after Kyle Larson, the sixth driver to go out in the qualifying order, endured a brief hiccup of power to his No. 17 Arrow McLaren-Rick Hendrick Chevrolet during a downshift off Turn 1 on his final of the four-lap run that led to aborting his maiden attempt.

Problems reared again when Arrow McLaren’s Pato O’Ward went out in the mid-point of the day for an initial run – after pulling out of line for his guaranteed first attempt – and suffered a similar fate.

Several other teams on late promising runs that tracked near transferring into the top 12 began to get hit with issues near the end of the day's running, including Conor Daly (Dreyer & Reinbold Racing), Augustin Canapino (Juncos Hollinger Racing), rookie Christian Rasmussen (Ed Carpenter Racing) and driver/owner Ed Carpenter.

What was the issue?

Even with the problems, Chevrolet was still represented by nine of the top 12 cars, including a front row sweep by Team Penske, who did not suffer any problems.

The issue was discovered as a plenum event, a result of a combination of factors that include the increased turbo boost levels. Rob Buckner, IndyCar program manager for Chevrolet, provided exactly what a plenum event entails.

“These engines are being operated on a knife edge here this weekend, and we're pushing for every bit of performance,” Buckner said.

“So on top of the cylinder heads in the air inlet system of the engine is a plenum, and there's some port fuel injectors up there, so while these engines are sustained high speed, that plenum is very full of fuel, and if we have any event over a downshift that can ignore that fuel, it ends up evaporating the plenum of its fuel air charge, temperatures rise rapidly, and it pretty much -- to the driver it's a perceived engine kill, and they vary in duration, they vary in severity.

“Unfortunately, here today, the ones we had were very noticeable to the drivers. Anything around Indianapolis is very noticeable to the drivers. It pretty much scrapped those runs, which we really hate for all those drivers that we impacted their day.”

Patricio O'Ward, Arrow McLaren Chevrolet (Photo by: Josh Tons / Motorsport Images)

Jim Campbell, vice president of GM Performance and Motorsports, provided his thoughts on the situation as the manufacturer presses towards its first Indy 500 pole since 2019 (Simon Pagenaud, Team Penske).

“We're pressing hard, and you can see obviously we're using the Indy 500-spec 1.5 bar,” Campbell said.

“There's been no testing at 1.5 bar with the exception of some time on Friday, no testing prior to that at 1.5 bar. This is a weekend where you put the higher boost levels in and you've got to go.

“What I would say is when you look at the Fast 12, super proud that nine of the top 12 are Chevrolets, representing five of our six teams.”

Campbell shared that all six teams that encountered the issues had no harm done to the engines. However, a sleepless night was on the table for everyone working for the bowtie brand ahead of Pole Day.

He added: “The team, our team is going to work here overnight, running in dynos around -- our dyno facilities around the world. We're going to be running overnight, and then we're working on ways to mitigate the issue and eliminate -- aero proof it for tomorrow around controls and calibration.

“Obviously there's some team strategy that will -- as the ambient conditions are clear for tomorrow, we have the forecast, but as we get closer to it, there's some decisions they can make, as well, so we'll be working with them on that.

“That's what I want to say. We're pushing as hard as we can. This year we have nine out of the Fast 12. Last year we had eight out of the Fast 12, but we did not get the pole last year, so we're pushing to get to the pole.”

When asked by during a press conference if there is a concern about shift points as a result, Buckner provided his assessment.

“Yeah, I think it seemed like one of the first couple laps with the full boost, it seemed pretty prevalent,” Buckner said. “We're going to look at everything, ECU data, shift points, shift lights.

“We're going to work with the teams, drivers. At this point there's really no mitigation strategy we would eliminate. Just wanting to have a clean day tomorrow, and we'll do everything we can for that.”

Buckner did not recall any “drastic” problems during Fast Friday running ahead of Saturday’s qualifying. Chevrolet also has no driver participating in the Last Chance, meaning all teams have made the race.

The focus is on tomorrow, Buckner said, when asked about the level of concern the issue is going into the battle for pole on Sunday.

“In my mind, top priority, we've got nine of the 12, so we've got a 75 percent chance at it,” Buckner said.

“I think we've got some really fast cars. I think all nine of those cars are capable of being on the front row. Our intention is to put three Chevrolets on the front row tomorrow, hopefully with no plenum events. We're going to keep working towards that.”

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