V8 Supercars champion Jamie Whincup has once again been well off the pace in the final practice session for the Townsville 400.

The Holden star, who has slipped to eighth in the standings after three consecutive race finishes outside the top 10, could only post the 19th fastest time in the 20-minute session on Friday morning.

Mercedes’ Will Davison continued his strong early form with the fastest lap of the session, a one minute and 13.0348 second spin around the Reid Park circuit.

Davison finished ahead of stablemate Ash Walsh (1:13.2908) and Holden’s Nick Percat (1:13.3199).

Whincup’s woes have forced Red Bull Racing to shuffle his race engineering line-up, with former engineer Mark Dutton stepping back into the role as they aim to keep the six-time champion’s title hopes alive.

Whincup has failed to break into the top 10 in any of the four practice sessions this weekend and admits his goal for Saturday’s 200km race is well off his normal standard.

“A win’s gonna be pretty tough for us. We’ve got to be realistic,” Whincup told Fox Sports.

“Of course we’re aiming for a win but a top five would be a great result for us today.

“I’m a confident person … I’m in a good place but life would be better if the car was fast.”

Championship leader Mark Winterbottom clocked the sixth-fastest lap of the session but again finished behind his teammate Chaz Mostert, who was fifth on the timesheets.

The Ford pair are cashing in while Whincup struggles and team manager Tim Edwards clearly has little sympathy for their great rival.

“We’ve got them on the ropes at the moment with the changes they’re making,” Edwards said.

“I’ve got no doubt they’ll come back (but) it’s nice to have the edge over them.”

The session was a disappointing one for Volvo’s Scott McLaughlin, who suffered an engine failure with 14 minutes to go which will force his garage to do some extra work before qualifying for Saturday’s race.

Qualifying starts at 1.10pm ahead of the opening race of the event from 4.15pm.