Shell and Gordon Murray reveal details of 100mpg city car

Detail changes to the engine include a friction-busting diamond-like coating (DLC) which was applied to the camshaft, tappets and piston skirts.

“The lubrication between camshaft and tappets is one of the most critical parts of the engine,” said Geo Technology’s director of engineering, Hidehito Ikebe. “To reduce friction, it is usually only necessary to coat one, but we applied it to both.”

To take into account the reduction in engine speed, the design of the retainer and valve springs were changed and titanium valves were installed. A new piston was designed, retaining only the original piston crown, which is important for the combustion process.

The piston skirt was shortened by 30% compared with the base engine and the contact surface with the cylinder was reduced by 40%. The recesses on the piston skirt which normally retain the lubricant were removed in favour of a polished contact surface of the skirt and the DLC coating.

The number of piston rings was reduced from three to two and the connecting rods were extended in length by 9%.

In combination, the myriad engine changes helped to “improve the weight distribution between top and bottom and reduce the friction when the piston is in motion,” explained Ikebe.

The car has now been handed over to Shell to undergo a testing programme, with the final vehicle due to be revealed in mid-2016. It will not be put into production; instead, it acknowledges trends that indicate three-quarters of the world’s nine billion inhabitants will live in cities by 2050.

“There is no intention to bring T.25S to market. It is a ‘capability analysis’ vehicle,” said Shell Lubricants innovation technology manager Robert Mainwaring.

The last project on which Murray, Goto and Shell co-operated was the all-conquering McLaren-Honda MP4/4 Formula 1 car, which won 15 of 16 races in 1988 with Ayrton Senna and Alain Prost driving.

The main mission of Project M is to draw together the most innovative aspects of lightweight engineering, streamlining and drivetrain efficiency.

It retains the T25’s ultra-compact rear-engined layout, utilising the principles of Murray’s unique iStream manufacturing process, which employs a simply fabricated tubular steel frame with strategically bonded-in composite panels to deliver low weight and immense strength without the complexity and inflexibility of the stamped steel components that are the basis of most cars.

Shell is at pains to emphasise the efficiency-building potential of modern, low-viscosity lubricants when integrated into the wider design of an economy car and its engine.

The original T25 used experimental low-friction Shell oils and returned 97mpg to win a London-Brighton economy competition, showing the potential of new lubricants to cut urban cycle fuel consumption by up to 6.5%.

Q&A with Gordon Murray (originally published April 2015)

What’s the main reason for your three-way deal?

"It’s a tripartite agreement to show the potential of true engineering cooperation. You can’t build a truly efficient car without pushing boundaries of light weighting, combustion, aerodynamics and low friction, which is what the three of us are doing."