Can anyone stop Richard Chamberlain in the Michelin Porsche Open Series? That's the question for race four at Oulton Park on Saturday 14 May as the Porsche 935 racer bids for his fourth win in four races.To date, Chamberlain has blitzed to victory at both Snetterton (twice) and Castle Combe in his fire-breathing 935 monster and he relishes the challenge of taming the mighty racer around the sweeps of Oulton Park.Rupert Lewin will again head the chase, having been forced to miss Castle Combe when clutch problems developed in his stunning 996 GT2-R. Lewin should be back for Oulton, as determined as ever to take the battle to Chamberlain.However, the arrival of Porsche ace Peter Cook for the Oulton race in his 911 GT2 could be the big threat to Chamberlain. Cook is right on home ground at Oulton and should be able to give the 935 a real fight!Class two will mark the race debut of Mark Stephenson in the ex-Rod Carman 911 GT3 Cup car. Stepping up from track days, the Cheshire driver knows the circuit well enough and will now tackle his first race in the car. He will line up against fellow racing newcomer Mark Allbutt in another 911GT3 Cup car in class two. However, it was Simon Mifsud who took his ex-Peter Chambers 911 GT3 Cup car to victory at Castle Combe.Class three featured a fantastic contest at Castle Combe with Jon Allen (993 Supercup) finishing just clear of a mighty three-way battle for second. Wayne Jackson (944 Turbo) and Mike Johnson (911SC) were in the thick of the action and will renew that rivalry at Oulton. For Johnson, this will be only his second ever race having made his debut at Castle Combe in the highly effective 3.8-litre 911SC that he also uses the Porsche Club Speed Championship.Finally, the Class 4 field for near-identical 944s is headed by Snetterton winner Charles Winterhalder and Frank Cortes.