Fortec Motorsports' Thomas Ingram Hill enjoyed a perfect start to proceedings at Silverstone, as the young Brit topped every session at the home of the British Grand Prix.
Ingram Hill started the day with a 2m02.427s, and followed that up with a lap a couple of tenths slower in session two. But it was his session three lap of 2m02.124s that proved the quickest, with a 0.235s margin to the rest of the field.
Elite Motorsport's Isaac Phelps was second fastest, just 0.014s ahead of Ingram Hill's teammate Jack Taylor in third.
Phelps' teammate Alex Kattoulas improved at the end of the day to go fourth overall, only 0.009s away from Taylor's Fortec and 0.035s clear of Douglas Motorsports' series newcomer Arjen Kraling.
Dayton Coulthard completed a good day for both him and Douglas Motorsport with the sixth fastest time, just under two tenths ahead of the third Elite Motorsport car of double Snetterton winner Ary Bansal.
Snetterton race winner Leon Wilson was eighth overall for Arden Motorsport, 0.048s ahead of the lead Hillspeed car of Leandro Juncos, while Fortec's Luca Magnussen completed the top-10 on his first day back in the car after appendix surgery.
Just 0.669s covered the top-10 runners across the day, while the lead 14 cars were all within a second.
The majority of drivers recorded their best times in session three, with championship leader Dan Guinchard, Megan Bruce and Dudley Ruddock the only drivers to set their best times at any other point, with all three posting their quickest laps in session one.
Two more test sessions follow on Friday, ahead of qualifying and race one on Saturday.
GB4 Championship, partnered by the BRDC, Silverstone Thursday test combined results:
1. Thomas Ingram Hill, Fortec Motorsports, 2m02.124s
2. Isaac Phelps, Elite Motorsport, +0.235s
3. Jack Taylor, Fortec Motorsports, +0.249s
4. Alex Kattoulas, Elite Motorsport, +0.258s
5. Arjen Kraling, Douglas Motorsport, +0.293s
6. Dayton Coulthard, Douglas Motorsport, +0.368s
7. Ary Bansal, Elite Motorsport, +0.565s
8. Leon Wilson, Arden Motorsport, +0.585s
9. Leandro Juncos, Hillspeed, +0.633s
10. Luca Magnussen, Fortec Motorsports, +0.669s
11. Dan Guinchard, Hillspeed, +0.679s
12. Mayer Deonarine, Graham Brunton Racing, +0.817s
13. Alex O'Grady, KMR Sport, +0.978s
14. Jason Pribyl, ADM, +0.984s
15. Enzo Hallman, Douglas Motorsport, +1.042s
16. Callum Baxter, Graham Brunton Racing, +1.158s
17. Megan Bruce, KMR Sport, +1.205s
18. Ava Dobson, Arden Motorsport, +1.209s
19. Stefan Bostandjiev, Pace Performance, +1.665s
20. Josh McLean, Pace Performance, +1.959s
21. Holly Miall, Fox Motorsport, +2.701s
22. Dudley Ruddock, Arden Motorsport, +2.744s
23. Lily May Watkins, KMR Sport, +3.851s
24. Flame Airikkala, Pace Performance, +4.047s
25. Caitlyn McDaniel, Fox Motorsport, +6.219s
