Races 10 and 11 in the Michelin Porsche Open Series form a Rockingham double header on Sunday (3 July) during the SCSA Thunder Sunday.Firmly on home ground and aiming for another brace of wins will be Richard Chamberlain in his fire-breathing 935. It's been a bit of an up and down year to date for Richard, with some car dramas, but if everything is back in running order he will be mighty around the Rockingham track.As ever, the biggest threat to Chamberlain will come from Rupert Lewin's 996GT2R, as the friendly rivalry between the two top cars in the series continues. Leading the chase of Chamberlain and Lewin will be Paul Howells (993 GT2) and Keith Butcher (911GT3R).Class two continues to be very open, but it is Mark Allbutt who heads to Rockingham fresh from a fine double at Donington in his 911GT3 Cup. Although a novice at the start of the season, Allbutt has made excellent progress and his confidence will have been boosted by the Donington results. However, his chief rival for class victory will be Tony Brown (964RSR), as Brown resumes his battle to take on the 911GT3 Cup cars in the division.Class three could be a three-way battle as Steve Burtt (993) and Wayne Jackson (944 Turbo) line up against series newcomer Marcus Clutton (3.2 Carrera). Having started the season in the Porsche Club Championship in a 911SC, 16-year old Clutton suffered more than his share of bad luck and has now switched to the Open in the ex-Colin Broster 3.2 Carrera.Meanwhile, another excellent battle amongst the 944s is set for class four. Charles Winterhalder and Alex Eacock have both been class winners this season, but Frank Cortes and series returnee Kevin Eacock could upset the form book.