Amongst the cool projects I’ve been party to this year is the latest reproduction from EB Motorsport: a flat-fan kit for air-cooled Porsche engines. Under development for the last two years, engineering for a flat fan kit started in the same way as most of the EB Motorsport product range: there was nothing else out there that did the job properly.

Porsche 911 RSR Turbo Replica

I’m not quite sure when EB’s Mark Bates decided he had to have a Porsche 911 RSR Turbo, but we definitely had a conversation about building a 2.1-litre Turbo replica soon after we started working together more than five years ago and the bodywork for the project is well under way (pic below). Since our first conversation, the EB Motorsport product range has expanded to include a lot of products that cross over from RSR to RSR Turbo, but the flat fan is all on its own when it comes to cool Porsche kit.

“If I could have bought a flat fan kit that looked correct and worked well at a sensible price, I wouldn’t have gone down the road of making it myself,” says Mark. “We did buy one kit but it was not what I was looking for, so we ended up doing it the long way.

Mark’s ‘long way’ would be most impossible for most of us, but nothing phases EB Motorsport. When your company has more than sixty years of experience manufacturing food-grade handling plant, including 30-metre-high composite silos that can hold tons upon tons of raw material, the minor details of re-manufacturing unobtainable throttle bodies, complex fuel pressure regulators and flat fan drives are not a big deal.

Flat Fan Components and Testing

That said, all high-end manufacturing takes time to do properly, and this has been done properly. The first step was to find a period composite fan, as making the tooling to replicate an air-cooled flat fan blade is not the work of a moment. That search came up empty handed, so a high-quality carbon fan was obtained that would hold up for testing. “Our own fan is in development, but it involves the most complex tooling we have ever designed,” says Mark. “It will take a while to get this bit right.”

The next step was the fan drive. The obvious way to recreate one of these was to buy an original 935 drive and reverse engineer it, so this is what happened. The process took six months, and the first test device was fitted to a static long block test rig earlier this year, connected to electric motors and tested for hours on end. EB measured details like noise, durability, horsepower consumption, backlash, shim dimensions and airflow with different internal diverters fitted to the custom EB fan shroud.

Flat Fan Horsepower Consumption

Testing revealed lots of interesting data, particularly in the areas of air flow and horsepower. “It’s long been rumoured that the flat fan costs a lot of horsepower due to the convoluted drivetrain, but a vertical fan will also cost horsepower,” says Mark. “Our testing proved that flat fan horsepower consumption was not linear but instead it increased exponentially. At 4k fan rpm, just 1.5 horsepower was lost, but at 12k rpm fan speed which is roughly 8k rpm engine speed, 32 horsepower was lost, mainly due to the volume of air being moved by the fan. Given the increased thermal protection to cylinders 1 and 4 offered by the flat fan installation, we’re comfortable with the test data.”

Tuthill Porsche Flat Fan 911

The video below shows the flat fan fitted to EB’s 2.5-litre ST engine on carbs, in a 911 supplied for road testing by Richard Tuthill. Tuthill Porsche will build the engine for the RSR Turbo replica and there’s even some discussion on building a short run of four RSR Turbo replicas, including EB Motorsport’s own car, all running flat fans and fun-horsepower big turbo engines. Now that would really be cool.

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