Mark Sumpter is concerned about his car's lack of speed following the fifth round of the Michelin Porsche Cup.

The Sussex driver consolidated second place in the series after taking fourth place in the sprint race at Silverstone last weekend.

But Sumpter knows his championship challenge needs to be stepped up if he is to land the title.

He said: "It feels like the engine has lost its edge. The car just feels flat and I think something isn't right.

"We're going to have a look at the engine data and see if we can find the problem."

Sumpter, from Five Ashes in East Sussex, qualified his Paragon Porsche/Ultrafilter-backed car in fourth place.

He was within a quarter of a second of pole position but was disappointed to be edged into fourth spot behind Mark Cole, Phil Hindley and Adrian Slater.

He said: "That's not too good, I should be faster round here. With the commitment I was putting in, I expected to be a bit faster."

In the race itself, Sumpter got a good start and edged ahead of Slater into the first corner. However, he soon knew that he could not fend off Slater, who managed to drag alongside on the exit of Luffield and then pull ahead past the pits.

That left Sumpter in fourth, with Nigel Rice chasing in fifth. As Slater set about challenging Phil Hindley for second, Sumpter and Rice started to close in but neither could make up any further places.

Sumpter said: "I was struggling to keep Nigel behind me and, even when Adrian and Phil were battling and slowing each other up, I was struggling to catch them."

The feature race provided Sumpter with another opportunity to make up points on series leader Cole but the race was halted after six laps and not restarted.

With oil spread around much of the circuit, the race officials decided that the circuit could not be made safe for racing in the time remaining at the end of the afternoon.

For the record, Sumpter was in third place and challenging for second when the race was stopped.