Hear the four-valve per cylinder, 493bhp (365kW), four-litre motor rev to 9000rpm

Earlier in the year, Californian tuning company Singer Vehicle Design announced that it would collaborate with Williams Advanced Engineering to develop a new engine upgrade for its Porsche 911 reimagined by Singer. After releasing renderings of the air-cooled, flat-six in August, an actual engine has found its way into a mule vehicle and testing has began.

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Singer has released a video of a silver 964 with, what looks like, hastily applied wide arches putting the new motor through its paces. The majority of the video is from within the car and you can hear the engine being revved to its red-line before going up through the gears. After seeing the car then decelerate from inside, the footage then changes to an external camera where you can hear that typically gravelly flat-six overrun.

Improving the engine that’s found in Singer’s current cars was a tall order considering that Cosworth had a hand in transforming the base Porsche engine into a 4-litre. The new unit was engineered around a brief to improve outright performance while also reducing weight in the engine bay but Williams has taken this to another level.

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Starting with a 1990-spec 3.6-litre flat-six, this latest upgrade increases capacity to a full 4-litres like previous Singer engines, but is then given four-valve per cylinder heads, titanium con-rods, aluminium throttle bodies and dual oil circuits among other modifications to liberate 365kW and a new, higher 9000rpm rev ceiling.

If you think these numbers seem remarkably similar to the ones of the latest Porsche 911 GT3 you would be right, but Singer didn’t stop there, enlisting the iconic Porsche Motorsport engine designer Hans Mezger as a mechanical consultant on the project.

Rob Dickinson, Founder of Singer Vehicle Design, explains: “Helping our clients realise their unique vision for a reimagined Porsche 911 with the help of automotive royalty is very much a privilege. Singer is delighted to be working with Williams Advanced Engineering and Hans Mezger to offer our clients a “next level” of restoration and modification services for their Porsche 911s.  With careful and dedicated development, this iconic air-cooled engine has much to give both its existing devotees and a generation of new enthusiasts.”