How teams have adapted to Formula One's seemingly perennial changes to its rules and regulations will be put under further scrutiny in the sweltering Malaysian conditions.

The decision to downgrade the size of the cars' engines from V10s to V8s was not universally welcomed and this weekend's race will test those who have hit the ground running and those with work still to do.

With its dusty desert setting, the season opener in Bahrain provided a stern test of the new motors. Now they will be given arguably their most rigorous examination of the year in sticky Sepang.

The temperatures and humidity are always a challenge around the fast, flowing track, but engines are now onto the second of the two race weekends which they must last or face a ten-place penalty on the starting grid.

Brazil's Felipe Massa may be the first to fall foul of this rule in 2006 with his Ferrari rumoured to require a replacement engine before the start of the weekend's running.

The teams are understandably concerned about performance so early in the season.

Simon Corbyn, head of F1 race engineering at Grove-based Williams F1' engine supplier Cosworth, said: "The Malaysian Grand Prix is one of the toughest for F1 engines.

"The high ambient temperatures are at the limit of what we experience during a race season and this places maximum demands on both the engine and car systems.

"This year will also be particularly challenging as this will be the first time any of the new V8 engines goes into a second race weekend.

"Engine reliability will be a significant factor, both in terms of the starting grid line-up and the race result in Malaysia."

The trackside engine chief for the Enstone-based Renault F1 team, Denis Chevrier, said: "The nature of the Sepang circuit lay-out, with the high-speed corners, means the drivers will spend 15 per cent more time at full throttle than last year."

"It will be a demanding weekend for the V8 and, at its conclusion, we will have a much better idea of how things stand for the first versions of the V8 engines in terms of performance and reliability."

Luca Marmorini, Toyota's engine technical director, added: "The first two back-to-back races make for a tough start to the year because of the heat of Malaysia, which will be 20 degrees higher than anything we encountered during pre-season testing."

The smaller engines' relative lack of horsepower means that the driver's right foot is on the accelerator for longer than it was in the V10 era, placing them under further strain.