Rob White explains the new Rebault D spec engine that will make its debut in Hungary this weekend.

A final evolution of the B spec was introduced in Hockenheim, and there is a new spec in Hungary. How pleased are you with progress on the engine, and with its overall performance?I am pleased with the progress made with the performance of the RS24 during the season, which is the result of a process that balances aggression and rigour, to advance the performance while managing the risks to maintain reliability, which is still the prerequisite for good racing results. While pleased with the performance, we are never satisfied so the whole Viry group will continue to strive to further improve the RS24 to power Fernando and Jarno through the final third of the season.

Can you tell us a little more about the D spec?The RS24D, racing in Hungary for the first time uses a revised cylinder head and related parts in the top end of the engine. The RS24D represents a small performance step over the final RS24B and will be the platform for further refinement and development during the final part of the season. There was an RS24C development project, which was pursued on the dyno, but which did not go in the car. Elements of the RS24C will appear in future versions of our engine.

Does introducing a new engine spec during a testing ban pose any particular problems?Although for base engine performance and reliability, it is the intention that track testing is confirmatory rather than exploratory, track testing remains an important final hurdle. It is also the first chance to gauge the subjective impressions of the drivers and an opportunity to work on the final calibration and set up of control systems. The timing of the test ban is known in advance, so must be considered in the planning and management of engine performance steps. Of course, the absence of track tests during August reduces the scope of changes that can introduced at races during and immediately after this period.