What It Takes To Hit 12,000-RPM With An Air-Cooled Porsche 911 Engine

If you haven't watched the video of Chris Harris driving the Tuthill Porsche 911k, do so immediately after reading this. The sound of its astonishing 11,000-rpm, air-cooled flat-six will haunt your dreams. That's mostly because only the uber-rich can afford one, which makes them out of reach for most mortals. But Tuthill's Porsche isn't expensive so wealthy tech bros can roll up to the office in something unique — it's expensive because, among other things, it isn't easy to make an air-cooled engine reliably rev like a superbike. And the company behind that literal fire-spitting Porsche, Swindon Powertrain in the UK, wants to make that possible for the masses. 

Swindon Powertrain makes a 24-valve cylinder head for Porsche's classic M64 engine (from either a 964 or 993-generation Porsche 911) that can make it rev to a claimed 12,000 rpm. The best part about it, though, is that it fits onto and works with a stock bottom end, so you don't need anything more than an old 911 for this kit to work. While Tuthill's specific engine is bespoke, Swindon's tech is what made its stratospheric redline possible. So, with its cylinder head kit, it's entirely possible that you can make your own ultra-high-revving 911 with the fan-favorite air-cooled Porsche engine.

Swindon set out to develop a cylinder head with four valves per cylinder (something Porsche never did with air-cooled engines), which allows the old Porsche engines to breathe significantly better at higher revs. Such improved aspiration gives the engine more power, but, more importantly, the extra valves help it rev higher. Having four valves in the same space that used to hold two means the new ones have to be smaller, and that means lighter. Lighter valves also means lighter springs. And that systemic weight reduction carries through the entire valve train weight, allowing the engine to rev even faster. 

Swindon will also provide CNC inlet porting to increase airflow efficiency, and you can even get special pistons and cylinder barrels designed for this cylinder head. Inlet airflow is said to be improved by 40% over a stock 993-generation 911's, and exhaust flow is up 66%. There's a power assisted steering drive adapter that allows you to use the engine's original power steering pump and other ancillaries. 

With its new lighter-weight valve train, the entire cylinder head weighs 7.7 pounds less than the original head, so it reduces a bit of mass at the back end of the car. That isn't anything monumental, but when you're trying to build the lightest-weight 911 possible (Tuthill's 911k weighs just 1,865 pounds!), those few pounds matter. And with the lighter-weight valve train, improved airflow, and all of the additional goodies Swindon can provide, you get an M64 engine that can rev to the moon. How fast you want it rev is up to you, as Swindon will make custom cam profiles to match your needs but claims up to 12,000 rpm is possible.

You don't need much else either. Okay, so you should probably make sure your M64 engine's bottom end is rebuilt, or at least in excellent condition, to ensure that it can handle the increased revs and power. However, Swindon claims that this cylinder head works with the engine's original crank case, chain drives, lubrication system, and exhaust system.

There's no official power output figures for M64 engines with this Swindon cylinder head, but that's because it can vary greatly depending on the application. That said, Swindon boss Raphaël Caillé reportedly claimed that a Swindon-equipped M64 can make around 125 brake-horsepower per liter. Depending on the engine, that could be between 400 and 450 bhp. 

Few cars on sale can reach engine speeds anywhere near 12,000 rpm. Gordon Murray's T.50 can (actually, it can reach 12,100 rpm), but that costs over $3 million. So, when you see the Swindon cylinder head's $50,234 price tag (at the current exchange rate from British Pounds to U.S. Dollars), it becomes more palatable with context. Yes, that's an enormous amount of money for a single cylinder head, as you can buy an entire 997-generation Porsche 911 for less. But there isn't a stock 911 on earth that can rev to 12,000 rpm.