Fortec Motorsport's championship challenger Nikolas Taylor set the best time of the day in the final GB4 test session of Thursday at Snetterton.
Taylor's time of 2m01.200s was four tenths of a second faster than anything seen so far in testing, and put him over a quarter of a second clear of the field.
Kevin Mills Racing's Jarrod Waberski was next up, 0.275s away from Taylor's pace and half a tenth clear of Hillspeed's championship leader Max Marzorati in third.
Megan Gilkes was fourth despite only completing six laps, and was 0.062s ahead of Waberski's teammate Tom Mills.
Jack Sherwood set the sixth fastest time for Elite Motorsport, 0.222s behind Mills and three tenths ahead of Fortec's Jessica Edgar.
Hillspeed's Marcus Short completed his first full day in a GB4 car with the eighth quickest time, 0.173s ahead of Graham Brunton Racing's Chloe Grant, while Fortec trialist Ceran Singh Sokhi was 10th.
Christian Lester completed his fourth session of the day but again didn't appear on the time sheets. Graham Brunton Racing's Logan Hannah will join testing tomorrow.
GB4 testing resumes at Silverstone tomorrow at 11.20.
GB4 Championship, partnered by the BRDC, Silverstone session
four result:
1. Nikolas Taylor, Fortec Motorsport, 2m01.200s
2. Jarrod Waberski, Kevin Mills Racing, +0.275s
3. Max Marzorati, Hillspeed, +0.327s
4. Megan Gilkes, Hillspeed, +0.999s
5. Tom Mills, Kevin Mills Racing, +1.062s
6. Jack Sherwood, Elite Motorsport, +1.284s
7. Jessica Edgar, Fortec Motorsport, +1.577s
8. Marcus Short, Hillspeed, +2.335s
9. Chloe Grant, Graham Brunton Racing, +2.508s
10. Ceran Singh Sokhi, Fortec Motorsport, +8.090s*
No time. Christian Lester, Rossoverde Racing