Asher Durham ended the day on top after the second Junior Superstock free practice session, beating Declan Connell by 0.039secs.
Durham, who sits fourth in the points and is one of four riders in the running for championship glory this weekend, set a fastest lap of 1min 38.345secs to go clear of Connell.
Aaron Silvester, who led the championship until dropping to second behind Owen Jenner at Donington Park, was third fastest with Sam Laffins fourth and Lewis Jones fifth.
Owen Jenner, who leads the championship by 15 points, completed just two laps before opting to sit the rest of the session out.
Pirelli National Junior Superstock with Santander Consumer Finance, combined practice result:
1. Asher Durham (G&S Racing) 1min 38.306s
2. Declan Connell (DC Racing) +0.039s
3. Aaron Silvester (A&J Racing) +0.597s
4. Sam Laffins (G&S Racing) +0.945s
5. Lewis Jones (Absolute Marquees Lewis Jones Racing) +1.504s