Andrew Irwin took his all-new Honda Racing Fireblade to fourth fastest in the opening practice session of the second round of the Bennetts British Superbike Championship at Snetterton, 1.123 seconds behind fastest man Danny Buchan of Kawasaki (one minute, 49.119 seconds).
Andrew, who is second in the standings, saw brother Glenn, who leads the way and is also on the Honda Racing Fireblade, claim sixth, a tenth of a second slower than his sibling.
The second fastest at the 2.97-mile Norfolk circuit was Kyle Ryde, with the competitors battling with strong cross-winds.
Andrew Irwin will begin today's first race from the back row after he was penalised for a racing incident with Josh Brookes at Donington, so he will be battling to make up as much ground as possible both to land points and put himself nearer the front of tomorrow's two races.
The fastest of the Ducatis was Christian Iddon in fifth position, with his Vision Track team-mate Brookes in eighth.
On a cloudy but dry day, the Irwins set their fastest laps on the 16th of 18 laps in the 45-minute session with Graeme Irwin - the third of the Carrickfergus brothers - down in 20th position in his BSB debut season riding the Team 64 Motorsport MET Healthcare Kawasaki.
Jack Kennedy, the British Supersport champion for the last two years, was over two and a half seconds off Buchan's pace down in 17th.
Another Carrick rider, Alastair Seeley, was fastest of the GP2 machines on his ABM Quattro, but was ninth overall in the mixed Supersport/GP2 class.
Double Donington Park Supersport winner Rory Skinner topped the time sheets from James Westmoreland and Lee Johnston, a mere 0.136 seconds splitting the trio.
Korie McGreevy (Century Racing Yamaha), who missed the opening session, bounced back on his second outing to record the eighth fastest time, a second and a quarter behind the Ashcourt Yamaha of Johnston.
With strong Irish representation in the Superstock 600cc Championship, Caolan Irwin, Adam McLean and Simon Reid were third, fourth and seventh respectively with just 0.389 seconds separating them.
Rhys Irwin, Sam Laffins and Eugene McManus finished the day inside the top 20.
Thirteen-year-old Casey O'Gorman, who is from Portlaoise but now based in Kent, was second fastest in the British Talent Cup outings in which 15-year-old Omagh Academy pupil Jamie Lyons was sixth fastest on his CCM Motors 125cc Honda.