Nico Rosberg's engine blew at the end of the Italian GP after he reverted to an older spec

The performance of the upgraded Mercedes engine that powered Lewis Hamilton to victory in the Italian Grand Prix has underlined the incredible pace of engine development in the hybrid era.

The full potential of what is essentially the prototype for Mercedes' 2016 engine was only really hinted at in the first practice session of Friday morning when they were being run in aggressive trim in an attempt at quickly highlighting any potential problems.

Thereafter, the units were turned down in the interests of reliability – and the engine in the back of Nico Rosberg's car had to be removed and replaced by an old standard-spec unit after suffering a leak in Saturday morning practice. But in P1 on Friday their end-of-straight speeds, combined with information gained by other teams via GPS-tracking suggested the new motor could have been as much as 40bhp more powerful than that which was already dominating the season.

It would be more accurate to say that the combined power unit and Petronas fuel was more powerful – for fuel technology has proven to be the most potent development tool in the hybrid turbo-charged formula since its introduction last year. It's a similar story at Ferrari, where gains of 40bhp have been made during this season, just from the fuel alone.

The heart of the Mercedes upgrade was a new fuel composition from Petronas that allowed a change in the combustion chamber shape of the engine. The fuel alone would not have made anything like as much difference with the old engine. Likewise, the new engine would not be as powerful as it is if the old fuel was used. It's a symbiotic process of development – "lots of small steps together that make one significant step in total," as Mercedes HPP boss Andy Cowell explained. "It all comes together beautifully."

The Mercedes were in a class of their own in Friday practice after introducing new engines at Monza

What the fuel and new combustion chamber shape combined allow is not just a bigger explosion in the combustion chamber – but a flame of greater duration, enabling the parts to be exposed to it for longer and thereby making the ignition less critical. This makes the engine more resistant to detonation – which is the chief limitation to power with this type of engine. Detonation is the phenomenon whereby the ignition becomes uncontrolled and uncoordinated with the delivery of the fuel mixture into the combustion chamber.

If it spontaneously ignites at the wrong time it can prove disastrous for the engine. The more prone the engine is to this uncontrolled ignition, the more conservatively its settings have to be to avoid it – and the less power it makes. Delay the onset of detonation with a new fuel composition and/or a better combustion chamber design and the engine can be run more aggressively, giving more power for the same fuel consumption or better fuel consumption for the same power.

This resistance to detonation is believed to be the biggest single advantage enjoyed by Mercedes over the rival Ferrari and, particularly, Renault, which is believed to be poor in this regard. This advantage compounds in the hybrid era, for the more power that is produced, the more heat that is created for the ersH to recover, giving greater electrical power too.

The necessity for the engine and fuel to be developed together in this formula was underlined last year when McLaren ran Mercedes engines as customers but was contracted to run Mobil fuel. Despite identical engines to the works cars, the McLarens were often as much as 40 horsepower down.

Ferrari have emerged as Mercedes' closest challengers in 2015

It is within that backdrop that Shell and Ferrari have just jointly announced a new five-year technical partnership. Closer collaboration than ever between fuel/lubricants and engines is necessary within the hybrid formula and a full team of Shell technicians work full time within the Maranello engine department.

Whether Ferrari can make the next step in its progress - from disaster in 2014, to race-winning respectability this year to title challengers in 2016 – could depend more than anything else upon the discoveries made by the Shell fuel chemists. After the warning shot across the bows that the upgraded Mercedes/Petronas motor represented at Monza, no rivals can be under any illusions that the bar is being raised ever-higher.

MH