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Romain Grosjean believes Lotus main deficiency is now power after the team made a significant step forward with the chassis at the last round in Spain.

Grosjean scored Lotus' first points in Spain with an eighth place finish, but qualified as high as fifth and was hopeful of a more competitive race had he not had a power unit issues. With Lotus finally understanding and extracting performance from the chassis, Grosjean said he was looking forward to Renault and fuel supplier Total unlocking more performance from the power unit.

"I think what we need is power and that's not something that I will feel easily," he said. "If you give me 20 horsepower more I will just go quicker on a laptime and I won't see the difference.

"That is where we are working and Total is doing a very good job and it is the third new specification of fuel that they bring and with a better fuel it gives more margin for the engine to work around a certain mapping. If the mapping better you have more power and so on. It's work between the engine, the fuel and the cars as well, the way they cool the engine and so on."

Grosjean said the improvement in Spain came from work in several different departments and is confident there is even more to come.

"I think there is a little bit of everything. They have worked on the understanding of the car and both sides [engine and chassis] have been working hard. We have improved the stability of the car, the aero, we improved the suspension and the mechanical grip.

"There is work in progress and there is more to come I am sure. It was good to be back in the top five in Spain and good to fight in the race for good points and hopefully we will keep developing the way we are doing right now."

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