Andretti Autosport continues to set the early pace at Indianapolis, with James Hinchcliffe ending the fourth day of practice with the fastest time.
Driving team-mate Marco Andretti's car, and leaning on a tow from Grahm Rahal, Hinchcliffe went to the top early in the afternoon with a 224.210mph lap that would ultimately remain the best time of the day.
Panther's JR Hildebrand came closest to toppling the Canadian with his 223.652mph effort, while Andretti took the same car that Hinchcliffe had used to the third-fastest time.
Helio Castroneves, Ryan Hunter-Reay and EJ Viso rounded out a sweep of the top six for Chevrolet-powered cars, with Josef Newgarden proving to be quickest of the Honda-powered runners.
Conditions were considerably warmer than they had been for the opening three days, which created challenges for some drivers as they worked to refine their set-ups.
"Today was the first day it has been warm outside, which was something I had not experienced yet," said Penske's AJ Allmendinger, who finished up 10th-fastest.
"The track changed throughout the day, getting slicker than it's been on the cooler days, but we were able to make adjustments that helped us put down some pretty good laps.
Almost all of the drivers that intend to attempt to qualify for the race were on track, with Buddy Lazier's self-run car the only confirmed entry still not to have turned a lap.
The third car entered by Schmidt Peterson Motorsport, which is rumoured to be earmarked for Jay Howard, is also yet to appear.
Several teams plan to make scheduled engine changes overnight, with Rahal Letterman Lanigan also planning to swap Rahal and James Jakes into their race cars after using the back-up cars during the opening days of practice.
Pos Driver Team Engine Mph Time Gap 1. James Hinchcliffe Andretti Chevy 224.210 40.1410s 2. JR Hildebrand Panther Chevy 223.652 40.2411s + 0.1001s 3. Marco Andretti Andretti Chevy 223.570 40.2558s + 0.1148s 4. Helio Castroneves Penske Chevy 223.556 40.2584s + 0.1174s 5. Ryan Hunter-Reay Andretti Chevy 223.332 40.2987s + 0.1577s 6. EJ Viso Andretti Chevy 223.138 40.3337s + 0.1927s 7. Josef Newgarden Fisher Honda 223.123 40.3365s + 0.1955s 8. Carlos Munoz Andretti Chevy 223.110 40.3389s + 0.1979s 9. Oriol Servia Panther DRR Chevy 222.093 40.5236s + 0.3826s 10. AJ Allmendinger Penske Chevy 222.005 40.5397s + 0.3987s 11. Marco Andretti Andretti Chevy 221.972 40.5456s + 0.4046s 12. Townsend Bell Panther Chevy 221.898 40.5592s + 0.4182s 13. Will Power Penske Chevy 221.654 40.6038s + 0.4628s 14. Sebastian Saavedra Dragon Chevy 221.119 40.7021s + 0.5611s 15. Sebastien Bourdais Dragon Chevy 221.088 40.7077s + 0.5667s 16. Simona de Silvestro KV Chevy 220.963 40.7308s + 0.5898s 17. Ed Carpenter Carpenter Chevy 220.897 40.7429s + 0.6019s 18. Charlie Kimball Ganassi Honda 220.722 40.7753s + 0.6343s 19. Tony Kanaan KV Chevy 220.645 40.7895s + 0.6485s 20. Simon Pagenaud Schmidt Honda 220.591 40.7995s + 0.6585s 21. Dario Franchitti Ganassi Honda 220.502 40.8159s + 0.6749s 22. Ryan Briscoe Ganassi Honda 220.100 40.8905s + 0.7495s 23. Tristan Vautier Schmidt Honda 220.017 40.9060s + 0.7650s 24. Scott Dixon Ganassi Honda 219.848 40.9373s + 0.7963s 25. Conor Daly Foyt Honda 219.688 40.9672s + 0.8262s 26. Pippa Mann Coyne Honda 219.588 40.9859s + 0.8449s 27. Justin Wilson Coyne Honda 219.423 41.0601s + 0.9191s 28. Ana Beatriz Coyne Honda 218.998 41.0962s + 0.9552s 29. Alex Tagliani Herta Honda 218.213 41.2442s + 1.1032s 30. Graham Rahal Rahal Honda 216.633 41.5450s + 1.4040s 31. Takuma Sato Foyt Honda 216.616 41.5482s + 1.4072s All cars Dallara DW12