Fernando Alonso was "very impressed" with NASCAR legend Jimmie Johnson's performance in a Formula 1 car in their drive swap test in Bahrain.
Two-time F1 world champion Alonso sampled Johnson's NASCAR Chevrolet, as the seven-time Cup champion drove a 2013 McLaren MP4-28 with a Mercedes V8 engine.
Alonso initially drove the F1 car for a few laps to set a benchmark time of 1m40.204s before switching to the Chevy.
Johnson managed to post a 1m40.462s during his F1 run, just over two tenths shy of the double world champion's best.
"Impressive," said Alonso of Johnson's performance. "He was really gaining time every run.
"Sometimes you put new tyres on these cars for the very first time and you are not able to extract the grip, but he was able to guess this extra grip that the new tyres are giving to you, and extract that grip into lap time so I was very impressed with that.
"He took it very seriously.
"We were swapping the cars, having fun, but also we wanted to feel the new environment in a representative way and in a speed that we could feel something close to what they feel normally."
Alonso, who competed in his final F1 race for now on Sunday in Abu Dhabi, admitted the NASCAR Chevrolet was a culture shock.
"I knew that the cars were very basic in terms of technology," he said. "Last time I ran an H-gearbox was in 1999, so it was going back a lot in time.
"The car was very powerful for the amount of grip available. Maybe with other cars around it is different but definitely alone it was a lot of fun."
Johnson, who had never driven a single-seater on a road course, admitted the "sensation of speed" was "mind-blowing".
He had to pit for helmet adjustments after his first run.
"Literally on the first outing, my helmet was trying to leave my head, and I was staring at the microphone in my helmet it was so high!" said Johnson.
"I was like 'I don't want to stop but I think I should...'
"I got my helmet more under control and then it was really my eyes trying to find their way far enough ahead and far enough round the turns.
"At the end I really quit focusing on the braking markers themselves and was able to look at the apex and had an idea of when to hit the brakes and was putting together some good laps. It was fun."
Johnson underlined that he was trying as hard as possible even though it was ostensibly a light-hearted day, and reckons the experience was better for him than for Alonso.
"I didn't know how close I would get," he said. "The racer in me was of course focused on that and I was straight away asking: 'What was his lap time? Can I look at the data and try and piece that together?'
"He had that same opportunity in my car to look at that data and go after it.
"I honestly think I got a way better swap experience than he did."