Holden's Jamie Whincup has posted the fastest time in practice for the Supercars event at Townsville.

The championship leader - a seven-time race winner on the Reid Park street circuit - clocked a best lap of one minute and 12.5530 seconds in Friday's second and final session.

Whincup finished ahead of Ford's Chaz Mostert (1:12.5995) with Holden's Will Davison coming in third fastest with a 1:12.7206.

Whincup's Red Bull Racing teammate Shane Van Gisbergen, who was all over the place in the day's earlier session, was fourth fastest.

Defending series champion Mark Winterbottom - who won both races at Townsville last year - was seventh quickest.

Holden veteran Craig Lowndes looks to have plenty of work to do ahead of this weekend's 200km races after finishing well off the pace.

Teenager Kurt Kostecki completed a solid first day behind the wheel of a Supercar as Lee Holdsworth's injury replacement, finishing ahead of Aaron Russell in practice No.2.

Saturday's action begins with qualifying at 2.55pm, then the first 200km race of the weekend starting at 6.10pm.