The 718 series of Porsche (Boxster, Cayman) has long been the 'baby' of their sports car range, but that doesn't mean they're not potent. Even with their turbocharged four-cylinder engines, they're still packing quite a lot of heat. But for some, a Porsche sports car must come with a six cylinder engine.

Built for purists: Porsche 718 Cayman GT4, Spyder are manual only image

Porsche has responded by shoehorning a massive 4.0-liter engine just behind the seats of the Boxster (in Spyder body style) and Cayman. The result is the 718 Cayman GT4 and the 718 Spyder GT4, the most powerful versions of the two cars yet.

How much power do they make, you ask? These cars each produce 420 PS and 420 Nm of torque from the flat-six engine. It doesn't sound like a lot, especially in an era of 600 PS sedans; but the Boxster and Cayman GT4s are light. Making its power output even more impressive is the fact that it's not turbocharged. Yes, the 4.0-liter engine in these cars are all motor, and rev up to 8,000 rpm.

Built for purists: Porsche 718 Cayman GT4, Spyder are manual only image

That gives both cars the ability to break the 300 km/h mark with the 718 Spyder topping out at 301 km/h, while the 718 Cayman GT4 can do 304 km/h. Both can do the 0 to 100 km/h sprint in 4.4 seconds. Purists should be delighted with the transmission too, as the GT4 models can only be had with a six-speed manual gearbox. No dual-clutches here.

Built for purists: Porsche 718 Cayman GT4, Spyder are manual only image

There are also visual cues that separate the GT4 models from the standard ones. Both get unique front and rear bumpers, along with a different set of alloy wheels exclusive to this particular model. In the case of the 718 Cayman GT4, it gets a fixed rear wing while the 718 Spyder has large pop-up spoiler. Porsche also gave both cars flat underfloors for enhanced aerodynamics. Of course, suspension upgrades and bigger brakes are part of the package.