Penske's two-time Supercars champion Scott McLaughlin says his neck was "torched" after testing an IndyCar for the first time on Monday.
McLaughlin, who won the 2018 and 2019 Supercars titles with DJR Team Penske, completed "around 140 laps" of the short course at Sebring with Penske's IndyCar squad as part of the championship's rookie testing programme.
McLaughlin told Autosport: "It was awesome, a really great day.
"For any driver preparing to drive an IndyCar, the simulator is such a good tool, because when I jumped on Sebring today, it was the first track I'd driven in an IndyCar for real but it was really good preparation.
"The only thing different was that my neck was getting absolutely torched with the g-loads.
"I was getting bashed from pillar to post, so that was a bit of an awakening experience. But it was really cool.
"I trained pretty hard and I was pretty good laterally with the loads.
"The team had put extra padding around my head, which I think is pretty normal for a new driver.
"But the first time I drove out of the pits and hit the brakes for the first time, I swore my helmet was going to hit the steering wheel! Unbelievable.
"I think I had been trying to just hold my neck up and not lean on the headrest.
"Once I started to actually use the stuff that was put in there to look after me, I was good."
McLaughlin said Penske "hid the times" from him, which he said was "pretty smart, because I'm a bit competitive" as the squad looked to gather data from the run.
The 26-year-old has made no secret of his interest in racing in America, and has been linked to a NASCAR switch.
Asked if he would consider open-wheel racing, despite having never raced a single-seater more powerful than a Formula Ford, McLaughlin said: "I've always said I'd race a wheelbarrow if there's a Team Penske sticker on the side!
"But I think the opportunity today to have a sample, to have a crack at an IndyCar was amazing, and it definitely answered a lot of questions for me regarding strength, regarding fitness.
"And it didn't feel too dissimilar to how I thought it was going to feel, which is good.
"But for me, I'd love the opportunity to be over here in the US, and I've always said that.
"I had a couple of little moments while I was just trying to find the limits of the car, but apart from that it was all good, and I didn't rip a corner off - that was the main thing."