Michael and William Dunlop will miss the final Carole Nash East Coast Irish road race tomorrow to take part in the Barry Sheene Memorial Trophy team races at Goodwood, part of the Revival meeting weekend.
The pair share a three-cylinder 500cc MV Agusta and finished second in yesterday's wet qualifying, a second behind the 500cc Manx Norton team of Jeremy McWilliams and Duncan Fitchett.
The Dunlops will line up against the likes of Bruce Anstey, Steve Parrish and former World champion Freddie Spencer, riding replica machines from the 1948-1966 era when Goodwood was home to British motor racing.
Wet weather also greeted competitors at the opening BSB practice at Silverstone yesterday, but that didn't deter Tyco BMW's Christian Iddon, who revelled in the conditions and splashed his way to the fastest time in the second session of two minutes, 26.184 seconds.
That was a second and a half ahead of defending champion Shayne Byrne and Josh Brookes, who despite a small tumble regained his composure and raced into third just as the chequered flag appeared.
Michael Laverty was back on form, taking sixth position on the McAms Yamaha, with second Tyco BMW rider Andy Reid 14th and Glenn Irwin down in 19th.
In the second Supersport practice on a drying track, Championship leader Keith Farmer was fifth fastest, 1.8 seconds behind Ben Currie on provisional pole. Dubliner Jack Kennedy was in second and Carrick's Andrew Irwin in third.
Richard Kerr and Eugene McManus were just inside the top 10 in Motostar practice while Kevin Keyes, Robert Kennedy and Aaron Clifford were fifth, 12th and 18th respectively in the Superstock 600cc.
The Superstock 1000cc saw Lisburn rider Carl Phillips finish in 19th and Josh Elliott in 25th.
The Irish Motocross Championship comes north today for the penultimate round at Tandragee MX Park with the Premier MX1 class being led by TM-mounted Dubliner Stuart Edmonds, who has a 33-point advantage over recently crowned Ulster champion Richard Bird (KTM) from Lisburn.
Jason Meara, from Loughbrickland, leads the Premier MX2 class by 20 points and young Dylan Stynes is in third, 70 points behind.
Racing starts at 11am.
Meanwhile, the 13th round of the MotoGP series takes place at Misano in Italy tomorrow and sitting out will be nine-time World champion Valentino Rossi, who suffered a broken leg in a recent training crash.
Rossi said: "I won't race at Misano or possibly the next round at Aragon in Spain. It's too early to say yet, but if I cannot come back at Aragon then it I will try for Motegi, Japan. It's a great shame not to be able to race at Misano, my home round, but I will work every day."
Yesterday's MotoGP practice was headed by Danilo Petrucci (Ducati) from Maverick Vinales (Yamaha).