Elite Motorsport's Isaac Phelps led the way, as the GB4 field got ever closer on the final day of testing at Silverstone on Friday.
The double race winner set a 2m01.575s lap in the first session of the day, which went unbeaten during the afternoon session.
Phelps was just 0.024s quicker than impressive Douglas Motorsport newcomer Arjen Kraling, who was just over a tenth of a second clear of the second Elite Motorsport car of Alex Kattoulas, who topped the afternoon session.
The remaining top-nine drivers all set their best times in the second session, with yesterday's pace setter, Fortec's Thomas Ingram Hill fourth on Friday, 0.042s ahead of the third Elite of Ary Bansal, with Arden's Leon Wilson just 0.029s further back.
Ingram Hill's teammate Jack Taylor was next up, just four thousandths of a second behind Wilson and 0.177s clear of the lead KMR Sport car of Alex O'Grady.
Hillspeed's championship leader Dan Guinchard was ninth overall on Friday, but only just over half a second away from tpp spot, and 0.012s ahead of Douglas Motorsport's Enzo Hallman, who completed a top-10 split by just 0.564s.
The top-15 drivers were all within a second of Phelps' effort, with qualifying next up at 9am on Saturday.
GB4 Championship, partnered by the BRDC, Silverstone Friday combined test result:
1. Isaac Phelps, Elite Motorsport, 2m01.575s
2. Arjen Kraling, Douglas Motorsport, +0.024s
3. Alex Kattoulas, Elite Motorsport, +0.149s
4. Thomas Ingram Hill, Fortec Motorsports, +0.277s
5. Ary Bansal, Elite Motorsport, +0.319s
6. Leon Wilson, Arden Motorsport, +0.348s
7. Jack Taylor, Fortec Motorsports, +0.352s
8. Alex O'Grady, KMR Sport, +0.529s
9. Dan Guinchard, Hillspeed, +0.552s
10. Enzo Hallman, Douglas Motorsport, +0.564s
11. Dayton Coulthard, Douglas Motorsport, +0.660s
12. Callum Baxter, Graham Brunton Racing, +0.720s
13. Jason Pribyl, ADM, +0.721s
14. Luca Magnussen, Fortec Motorsports, +0.860s
15. Leandro Juncos, Hillspeed, +0.908s
16. Mayer Deonarine, Graham Brunton Racing, +1.001s
17. Ava Dobson, Arden Motorsport, +1.129s
18. Josh McLean, Pace Performance, +1.155s
19. Stefan Bostandjiev, Pace Performance, +1.229s
20. Megan Bruce, KMR Sport, +1.364s
21. Dudley Ruddock, Arden Motorsport, +2.085s
22. Flame Airikkala, Pace Performance, 3.261s
23. Lily-May Watkins, KMR Sport, +3.289s
24. Holly Miall, Fox Motorsport, +3.330s
25. Caitlyn McDaniel, Fox Motorsport, +4.322s
