Lotus driver Kimi Raikkonen tested a GP3/13 car at the Circuit de Catalunya in Spain on Friday in order to assist the development of the series.
Raikkonen tested the car on different compounds of tyres in order to help with developments for next season.
The main aim of the test was to find solutions for GP3's difficulty with overtaking this season, according to the series.
Raikkonen completed 58 laps, with a best time of 1:34.780.
"I wanted to test the GP3/13 because my friend Afa Heikkinen has a team in this Series [Koiranen GP] and I have been closely following their progress and results since the beginning of the season," he said.
"I was curious to see how the car handled and it was actually fun to drive. There were a few issues regarding its behaviour, but we managed to solve most of them."
"The GP3/13 is a very good tool for young drivers, especially when you have to learn about tyre management like we have in F1."
GP3 Series technical director Didier Perrin thanked Raikkonen for his help.
"We are extremely pleased to have had the opportunity to work with Kimi today," said Perrin.
"His experience and feedback were invaluable and they gave us a better understanding of what needs to be done in order to make our car a better tool in overtaking opportunities for next season."
"He has confirmed all our hypothesis, and together we could start working on two development directions for the end of season testing. We would like to thank Kimi for testing with us today and Koiranen GP for helping make this possible."
Marussia young driver Tio Ellinas currently leads the GP3 Series, with the championship set to resume in Belgium next weekend.