Red Bull Ampol Racing’s two cars combined for nearly 1000 kilometres of pre-season test running at Queensland Raceway.
Matt Stone Racing youngster Zane Goddard topped the time sheets with his flyer set in cooler morning conditions.
However, as the heat settled over Queensland Raceway, teams turned to fine-tuning their cars and completing simulation runs.
YellowCover Racing driver Goddard set a 1:09.0257s early on, and completed 78 laps.
Dick Johnson Racing recruit Anton De Pasquale, who completed 96 laps, was second fastest on a 1:09.0318s, just 0.0061s adrift of Goddard’s lap.
Goddard’s Matt Stone Racing teammate Jake Kostecki was third on a 1:09.0404s, but completed the fewest laps of the day with 57.
The top three were covered by a meagre 0.0147s.
The Triple Eight entries were fourth and fifth, with Jamie Whincup and Shane van Gisbergen sharing their cars with their respective co-drivers Craig Lowndes and Garth Tander.
The #88 and #97 entries completed a combined 297 laps of the 3.12km Ipswich circuit, having combined for over 170 laps by the six-hour mark.
The defending Bathurst-winning combination of van Gisbergen and Tander car logged the most laps on the day with 166; a total of nearly 518km.
Whincup and Lowndes, meanwhile, recorded 131 laps and over 400km of running.
All up, the two Triple Eight Commodores covered a whopping 926km on the day, but Whincup admitted gains are yet to be made pace-wise.
"We spent most of the day just trying to go faster, trying to learn mechanically how to make the car quicker," said Whincup, who has made ergonomic tweaks to his car for the new season.
"Got a lot of data, but not sure if we made any gains forward, but we got a lot of information, so hopefully we can go through that and make some gains."
DJR recruit Will Davison logged 90 laps, the same as Team Sydney's Garry Jacobson.
Jacobson's teammate Fabian Coulthard combined with team owner Jonathon Webb to help the #19 Local Legends entry to 66 laps.
Van Gisbergen was frustrated by the changing conditions, with the heat making it difficult to chase time.
However, the day gave both drivers a chance to work with their new engineers ahead of the return to Bathurst later this month, with David Cauchi shifting to van Gisbergen’s entry.
Former Matt Stone Racing engineer Wes McDougall will skipper Whincup’s car in the seven-time champion's final full-time season before retiring at the end of 2021.
"It was pretty hot, which sucks, but it's awesome to be back in the car," van Gisbergen said.
"Just getting used to it, trying a couple of programmes on both cars.
"Myself learning Cauchi, and Jamie learning with Wes. Couple of new engineers for both of us, but it's been pretty good.
"We'll see what we can learn, our cars aren't much different to [October at Bathurst].
"A couple of things today we've found, some have worked, some haven’t."
Victorian-based teams will hit Winton Motor Raceway on Friday February 19 for official pre-season testing.
The 2021 Repco Supercars Championship will commence at the Repco Mt Panorama 500. Tickets are on sale now.
Most laps at official pre-season testing (Queensland Raceway)