BMW's secret McLaren F1-engined BMW M5 Touring

For many, the 6.1-litre V12 nestled in the middle of the McLaren F1 is the finest production engine ever built.

What might not be common knowledge is that the test bed for the mighty S70/2 was a BMW E34 M5 Touring, this prototype surely ranking as one of the coolest cars ever created.

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The information came to light on the Collecting Cars podcast, hosted by Top Gear presenter Chris Harris, during an interview with classic car dealer and racer David Clark, who acted as the Director of McLaren road and race cars from 1994-1998.

“When they tested the engine it was in an M5 estate car,” explains Clark. “I’ve driven, it’s an outrageous thing.” This is unsurprising, as shoehorning the McLaren’s V12 into the E34 M5 essentially doubled its performance potential.

Developed by BMW’s engine guru Paul Rosche, the S70/2 developed 461kW at 7400rpm and 650Nm at 5600rpm, a far cry from the M5’s 232kW/360Nm, which itself was extremely impressive at the time for a four-door sedan. Or five-door wagon.

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According to Clark BMW still has the car, one of many secret prototypes it has stashed away including the E31 M8 supercar and rear-engined V16 7 Series. The E34 M5 Touring is itself a special piece of machinery, being the last hand-built M car with just 891 produced.

“The engines are so amazing,” says Clark, who remains one of the world’s foremost authorities on the McLaren F1 and has a huge collection of spare parts. “I remember going to see Paul Rosche, I flew back with Gordon [Murray] and said ‘Gordon this is never going to happen, it has to go before the [BMW] board, this is a big, big thing.

“Anyway, it happened quite quickly with [then BMW Motorsport chief Karl-Heinz] Kalbfell and Rosche and the engine just evolved – it could never happen today in the way that it did.”

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Nevertheless, as amazing as it was, the program was not a financial success. With the F1 launched at the tail of a major recession, Clark reveals one of his first moves was to wriggle McLaren out of the proposed 350-engine contract with BMW. It was a shrewd move, as just 71 road cars were produced with 106 in total.