The Erebus Motorsport driver clinched top spot in the Top 10 Shootout as the seventh runner in the session.
Speaking after the session, Kostecki said he suffered “double vision” at the end of Conrod Straight.
“I’ve had a couple sets of [bad] tyres this weekend so far,” said Kostecki.
“Just put brand new ones on and [it] feels like I’m in a salt shaker. It was a bit surprising then, to be honest. That was the worst I felt.
“It was getting pretty hard to see at 270 km/h plus. Going into the kink at the Chase was a bit interesting.
“So just something we’re going to have to keep our eye on tomorrow.”
Despite taking pole position last year, Kostecki said this year’s effort was something of a surprise.
The 2023 champion said the year-on-year development in Gen3 machinery had left Erebus Motorsport playing catch up.
“Probably a little bit more unexpected this year, to be honest,” said Kostecki of his pole position.
“We spent a lot of time working on the race car, probably somewhere we were a bit weak last year.
“It was a little bit sort of nervous going to the Shootout, not sort of knowing how the car was going to react pushing to the absolute limit. The car was awesome in the Shootout.
“Big thank you to the whole team and George [Commins, race engineer] has done a fantastic job bringing it into the window the whole weekend.”
Kostecki will want to go one better than his 2023 efforts.
Last year, he and David Russell finished runner-up to Red Bull Ampol Racing’s Shane van Gisbergen and Richie Stanaway.
For this year’s Great Race, the team has enlisted one of van Gisbergen’s former race engineers Blake Smith, who worked with the Kiwi a decade ago in his ill-fated 2014 effort.
“We didn’t really have a good strategy last year,” said Kostecki.
“We made a few mistakes during the race. And, you know, let the Bulls get in front of us. It’s pretty hard to pass from there and just made a few more mistakes leading on from that.
“We’ve got some manpower this year to help us with that. So it was great having Blake onboard at Sandown. We just have to focus on ourselves.
“We know we’ve got a fast race car. We’ve just got to minimise the mistakes.
“Being that the Full Course Yellows are now in from last year, the race is going to be that much different.”
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Kostecki will also be hoping a stomach bug doesn’t rear its ugly head on race day.
Although he didn’t specify what he had been suffering from, New South Wales is in the midst of a gastroenteritis outbreak.
“Been feeling a little bit off,” said Kostecki.
“There’s a bit of a bug going around. Feeling a lot better today but I’ll be fine by tomorrow.
“Didn’t really have the best of days yesterday but glad to be on the mend.”