Time off the track appears to have done little to help Ford’s chances of wresting the V8 Supercars crown from the clutches of their Holden rivals after struggling on day one of official testing.

Reigning Bathurst winner Mark Winterbottom and his three Ford Performance Racing (FPR) stablemates failed to post a lap fast enough to crack a top 15 dominated by Holden and Nissan at Sydney Motorsport Park on Saturday.

The day was no kinder to defending five-time champion Jamie Whincup, who was more than 1.5 seconds off the lead pace set in mostly-wet conditions by Fabian Coulthard.

Whincup spent most of the day out of the rain and in the garage, while teammate Craig Lowndes laid down the day’s fourth-quickest time.

“That was always going to happen with a new engineer (in David Cauchi),” Whincup told AAP.

“The best thing is we got back on track at the end of the day.

“But, yeah, we’ve got plenty of work to do. We’ve got a big couple of weeks coming up to get the No.1 car really firing for Adelaide.”

All 25 cars from this year’s five manufacturers were put through their paces, but it was Nissan that seemed to benefit most from a slew of off-season changes that included a new rear wing and other aerodynamic features.

Kelly brothers Todd and Rick consistently posted times within the top-five, while the Nissans of James Moffat and Michael Caruso were among the 10 quickest.

“(The car) feels really good but today’s been an interesting day, so you can’t really put too much on it,” Kelly said.

“The conditions were constantly changing and people are running different tyres all the time.

“Certainly, the pace we had in the morning session – basically in the top two or three the whole time – was pretty genuine.”

Newcomers Volvo made a smooth but unremarkable start to their debut season in V8 Supercars, posting the 17th and 19th fastest laps of the day.

Meanwhile, former FPR racer Will Davison was anchored at the bottom of timesheets with a disheartening start to his year with Erebus Motorsport.

The season-opening Clipsal 500 begins in Adelaide on February 27.