John Horsman, who developed the Porsche 917 into a Le Mans-winning machine, has died at the age of 85.

The engineer and former RAF officer worked alongside team manager John Wyer for decades, and played a key role in the success of the Ford GT40, Porsche 917 and Mirage GR8 at Le Mans.

Horsman’s Gulf-liveried cars won three world sports car championships and three Le Mans 24 Hour races. Derek Bell, Jacky Ickx, Pedro Rodriguez, Jackie Oliver, Richard Attwood and Jo Siffert are among the drivers who won in a Horsman car.

After months of being a monster, the 917 was tamed

His greatest moment came in 1969. After two successive Le Mans victories with the Ford GT40, Wyer and Horsman were switching their efforts to the new Porsche 917, with backing from the factory.

But the flat-12-powered Porsche had proved fearsome in its first races that year. Rear lift at high speed was so alarming that some works drivers refused to race it. Vic Elford wrote that the Mulsanne Straight wasn’t wide enough to get the car to run straight.

Enter Horsman and a mid-autumn test at Zeltweg where the air was heavy with flying insects, making their mark on the front of the cars.

“I noted there were hardly any dead gnats on the rear spoilers,” Horsman wrote in his biography, Racing in the Rain. “Since they are very small and light, I knew the gnats would flow over the bodywork exactly as the air flowed, and similar to the smoke from wands used in wind tunnels.

“I knew immediately that we had to raise the rear deck and then attach small adjustable spoilers to the trailing edge. It was obvious to me that if the whole rear body surface was in the airstream, it would be able to exert some downforce.”

With limited equipment and testing time, modifications were necessarily crude: sheet aluminium cut with tin snips and hammered against Armco barriers, which Horsman described as “very ugly”.

The trackside tweaks had a transformational effect on the car, however, with Brian Redman the first to realise the benefits. “Brian stayed out, lapping a little faster each time around,” wrote Horsman. “At the end of [seven] laps he came in and said, ‘That’s it — now it’s a racing car!’

“After months of being a monster, the 917 was tamed.”