A month after the contender s in the Porsche Carrera Cup GB tackled the challenge of the Croft circuit in North Yorkshire, it is the turn of the drivers in the Porsche GT3 Cup Challenge GB to head to the Darlington track for a pair of races next weekend (21/22 July).The Porsche GT3 Cup Challenge is managed by Porsche Cars GB alongside the Carrera Cup GB and is growing as the season develops, with steadily building competitor interest. The series gained championship status this year for the six-event, 12-race season and is for the cars from 2009 or before, including the 996-model cars from up to 2006.Few, if any, of the GT3 Cup Challenge drivers have much experience of Croft, a circuit that blends slower-speed technical sections with fast and flowing high-speed sweeps. It is a real drivers challenge and they will be drawing on the data accumulated when the teams were at Croft last month with the Carrera Cup.Heading the GT3 Cup Challenge GB entry into rounds seven and eight will be championship leader James Birch (IN2 Racing), who has scored an impressive run of five wins from six races run to date. However, Birch will not have an easy run at Croft as Steven Liquorish (Team Parker Racing) is chasing hard and is determined to try and reduce the 17-point advantage that Birch has built up.Two drivers stand out as the big challengers to Birch and Liquorish. Birmingham-based Irishman John Ferguson (ASK Racing) is another driver needing to learn the Croft track, but he showed at Thruxton that he can quickly get to grips with challenging tracks. Meanwhile, back on the grid after missing Thruxton is former single-seater ace Justin Sherwood (Team Parker Racing), who is also lacking knowledge of the Yorkshire track.For Mark Cowne (Team Parker Racing), every track is a new challenge as this is his first year of racing, but hes learning fast and showed excellent form at Thruxton. A first overall podium is his target for the balance of the 2012 season.After qualifying at 11.15 on Saturday, round seven will start at 16.50, with round eight at 15.30 on Sunday. Both races will be filmed for transmission on the Porsche Origin website and Porsches YouTube channel.Current provisional championship points:Overall: 1 James Birch, 110; 2 Steven Liquorish, 93; 3 John Ferguson, 69; 4 Neil Houston and Mark Cowne, 60; 6 Peter Smallwood, 57; etc.Class 2: 1 Mark Cowne, 28; 2 Tom Hallissey, 11.