Romain Grosjean says his run to the fourth fastest time in qualifying for the Belgian Grand Prix is testament to what could be possible at Lotus with some development, speculating it could be missing upwards of half-a-second.

The Frenchman produced his and Lotus' best qualifying performance since the 2013 Australian Grand Prix by going fourth, though a gearbox change earlier in the weekend means he will be forced to serve a five-place penalty, placing him ninth on the grid.

The result comes as Lotus finds itself shrouded in ongoing matters off the track, including the potential sale to Renault for 2016.

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However, Grosjean praised the effort of the direct team around him, but says had Lotus been able to develop the E23, it could be good enough for podium finishes or even races.

"I think it shows a strong group of people here. I've said, from day one with this car, the baseline was very good and, with some development, it could become a very good car.

"It shows that we know how to produce a really good car, a podium finisher or winning car, but we've not had much development this year and, if you just imagine a five-tenths development on the car, it would be very close to Mercedes."

Reflecting on the lap itself, which came on a day when the Mercedes-powered cars locked out seven of the top ten starting positions, Grosjean says the team was initially only targeting P11.

"It was a great qualifying. Initially, we thought qualifying P11 would be good, saving a set of tyres and, with the five-place penalty, starting P16.

"Then Q2 went very well and, in Q3, we just gave it everything and it worked well, so I think we are pretty much surprised with P4 but it shows that we have been working in a good direction."