Indycar champion Scott Dixon has set his sights on a move to Formula One next year after his first experience of a Grand Prix car.
Dixon showed well in his first test of an F1 car
The New Zealander, 23, tested for BMW Williams last week and is due for another run in the car next month.
"It's definitely what I want to do. I would get back in the car today if I could," Dixon told the AFP agency.
"Those cars shocked me. It was unbelievable for the first 20 laps. But I slowly got into it."
Dixon drove at the Le Castellet track in the south of France and was only 0.4 seconds slower than Williams race driver Ralf Schumacher.
Dixon will have three days in the car at Barcelona's Circuit de Catalunya next month for the team to fully assess his potential - Le Castellet is renowned as an unchallenging track that makes it difficult to measure cars and drivers.
Dixon said: "I had a smile from ear to ear all day."
He drove 59 laps in one of this year's FW26 Williams cars, with a fastest time of one minute 11.753 seconds.
That was an impressive fourth fastest among the nine drivers testing on Friday and compares to Schumacher's 1:11.330.
Dixon said he had been stunned by the F1 cars performance compared with the Indy Racing League car he is used to.
"The biggest difference was the braking and the tyres," he said. "The tyres last for about one lap. You have to go out slow on your out lap and then go as fast as you can on one lap."
He said the g-forces under braking and cornering were "huge".
"I lasted about three runs before my neck was done. You just can't hold it up," Dixon said.
"The acceleration isn't too bad because your head is resting most of the time, but the g-forces turning and the braking in the braking zone, your head goes down and
you have to slowly bring it up. The forces are way more than what we get."
He said he was also amazed at the vast array of
gadgets in the cockpit of an F1 car.
"It's a mess," Dixon said. "There is crap everywhere. There are probably 40 buttons on the wheel. It's out of control."