The late-season engine developments from all four manufacturers have been all about using up the remaining 2015 development tokens. In that way, 2016 tokens are not wasted. Although only the upgraded Mercedes and Honda have actually been run in a race so far, so long as the engines are tested or appear in a practice session the tokens count as having been used. But, together with Ferrari’s combustion upgrade at Monza and Renault’s as-yet un-raced similar upgrade, they illustrate how much of the advances are about fuel development.

Mercedes introduced what was essentially the prototype of its 2016 engine at Monza. In Austin a revised Honda made its debut in Fernando Alonso’s McLaren. The new narrow-block Ferrari engine – its architecture an intrinsic part of the 2016 car – that was possibly going to be used by Kimi Räikkönen in Austin still needs further dyno mileage before being signed off and, furthermore, it requires a small change to the gearbox casing.

The new Renault readied for Austin will not be run until Brazil at the earliest, as Red Bull did not wish to take the grid penalty at Austin, a track it expected to provide one of its best chances, especially given the weather. In Mexico, the extra cooling required demanded a different installation for which the new engine isn’t configured.

The combustion chamber design, the fuel composition and how they interact with each other are where the big gains are in this formula. The heart of the hybrid power units remains the internal combustion engine – and maximising that combustion gives a compounding advantage as it gives the MGU-H more heat to work with. Bruce Crawley, motor sport technology manager at McLaren-Honda suppliers ExxonMobil – which provided the fourth evolution of its 2015 fuel for Alonso’s engine in Austin – recently gave some further background to the process.

“We are regulated around the European road car fuel specification in terms of octane and the physical and chemical levels. So this fuel would work in a road car. But within that spec we have a lot of room to improve the performance of these engines.” There’s common talk in the paddock of 40bhp gains having been made from fuels alone this year. But typically that can only be accessed once the engine is at a mature stage of development.

“The mechanical architecture, the choice of materials, subtleties of design – all these things make a difference to the fuel composition,” says Crawley. “In NASCAR we supply both Chevrolet and Toyota, but the fuels we do for them are totally different. It’s the same here; the fuel we do for Honda is very different to where we were with Mercedes. The engine is still evolving – and so we’re following that. Our development is very much determined by Honda. It’s more about how quickly they can move with their development than how quickly we can move – at this stage.”

This is in contrast to the recent Mercedes update, which was very much initiated by a fuel development. A change in the fuel’s composition allowed a better combination of energy release and combustion duration – but it needed a change in combustion chamber design to fully access this. It’s an indication of the differing stages of development the two engines are at.

“There’s an ongoing optimisation loop to be made as the engine and fuel develop. The fuel has a high energy content and in an ideal world you’d convert that energy to useful work with 100 per cent efficiency. But in the real world, balanced against how much of that energy you can convert is knock resistance (which combats premature fuel ignition). Broadly, the more energy you put into the fuel, the worse the knock resistance is.

“The challenge is therefore to give the maximum energy content possible but still with very, very good knock resistance. The regulation is good in that it gives a major technical challenge. I’m not sure how much that was understood when the regs were written, but that’s the outcome and it’s made it an exciting time for fuel development.”

Getting the combustion to last longer helps with knock resistance, but is broadly more difficult to achieve the higher the energy content. The idea is to get the engine/fuel on just the right side of that power/knock trade-off. Essentially the fuel manufacturer is trying to facilitate the engine designer being as aggressive as possible.

One of the challenges facing the engine manufacturers has been in choosing the optimum fuel pressure (limited by regulation to 500-bar) in these direct injection engines. The greater the pressure, the more fuel atomisation and, in theory, the better the combustion. But even that’s not a straightforward equation, as Crawley explains.

“Because that’s more a Honda area than a Mobil one I can’t really comment on that other than to say it’s an issue of mechanical design and how much control of the combustion you’ve got. Any change in the combustion system – combustion chamber shape, compression ratio, boost pressure, exhaust scavenging – changes the speed of combustion and we can accommodate that with the fuel’s composition. Those things change where you are on that trade-off between knock resistance and power. Our challenge is to enable the engine designers to be as aggressive as they want to be on a whole range of design points.”

That’s without even taking into account the implications of the MGU-H and its thermal energy recovery. This too feeds into that optimisation loop in terms of changing where the optimum exhaust scavenging point is – and this of course has implications upon the combustion. Is there more lap time to be gained by increasing the combustion efficiency of the internal combustion engine or from creating more heat for the MGU-H to use? That point will change along with developments in the engine and fuel.

In terms of lubrication, development is perhaps not as spectacular as with fuel, but still ongoing.

“The development programme with lubrication is just about minimising friction. We’ve mapped the engine for its friction characteristics and we are aware that there is performance to come [from Honda] on that. Because race engines have a dry sump there are parasitic losses involved in spraying oil into the engine and removing it and we have done things with the oil technology to get there.

“The two main ones are mechanical friction reduction and oil temperature and flow rate. The oil is being used to cool the engine far more than in a road car – to the piston area in particular. Oil is not as good thermally as water for cooling but it’s still doing up to 30 per cent of the total cooling – as you can see by comparing the size of the water and oil radiators.”

The main challenge in F1 gearbox oil technology is in optimising its transition from a liquid to a semi-solid state and back to liquid as it encounters the super-high contact pressures in the gear contacts. The chemistry of that transformation is part of what allows the gearboxes to be so miniaturised. It’s also what allows them to survive some extreme abuse.

Gearbox malfunctions for the McLarens in Singapore caused them to be running so hot that the sensors were melted – and yet the gearboxes were not destroyed and are expected to be used again. Similarly, in Brazil 2011 Lewis Hamilton retired after his gearbox selected a false neutral. The sensors instructed it to because of an oil leak and subsequent temperatures of over 200-deg C, way beyond what the oil was designed for.

“The subsequent discussion was should we have over-ridden the fail-safe, because as it turned out the ‘box was still OK. It’s risky because when you switch your sensors off you have no idea what’s happening in there. But it’s amazing what a gearbox will actually withstand.”

Lab technicians making subtle changes to chemical compositions are probably responsible for more lap time gains this year than the aerodynamic departments.