Words: Calvin Chan
Photography: Calvin Chan / Porsche
Published: June 14, 2021
The writing's on the wall for naturally aspirated (NA) engines. What used to be the most common type of engine has now transitioned into one of the rarest. Motors without any kind of plumbing are becoming scarcer by the minute, as automakers route their R&D spending into cleaner forms of mobility. Gone are the high-strung VTECs from Honda and exotic flat-plane crank V8s from Shelby. Small displacement motors married with turbochargers and lithium-ion batteries are the new norm. Just ask Mercedes-Benz who just announced that their next-generation C 63 AMG will replace the V8 with a diminutive four-cylinder.
That being said, there are still a few gems fanning the dying flame, like the Lexus 5.0-litre V8 nestled under the hood of the LC 500, the 6.4-litre HEMI V8 motivating the Dodge Charger SRT, and the small-block LT2 V8 mounted in the middle of the new Chevrolet C8 Corvette Stingray. Lamborghini has been holding off longer than most with its stratospheric V10, but even storied brands like Ferrari have begun to make the inevitable shift.
But why is that a bad thing? Turbochargers add a significant amount of horsepower and low-end torque, but they clog up the mechanical acoustics, and many of the distinctive notes characterized by the engine’s shape and form are lost in transition. Power delivery becomes nonlinear, high RPMs are capped off, and you no longer have to work hard to extract performance. Turbos hand you torque on a silver platter, whereas NA engines need to be wrung out, subsequently adding to driver engagement. And like manual transmissions, none have been a bigger proponent of keeping NA motors alive than Porsche.
Back in 2019 when most sports car manufacturers were hopping on the bandwagon of smaller turbo engines, Porsche went ahead and announced their brand new, 4.0-litre flat six-cylinder engine, which was, you guessed it, naturally aspirated. Set to underpin the 718 Boxster and Cayman GTS 4.0 models, that meant Porsche not only found a way to make it fuel efficient, but also dynamically relevant in today’s market filled with high outputs and meaningless Nürburgring claims. Marc Ouayoun, President and CEO of Porsche Canada, tells us that “the GTS 4.0 models will appeal to those who wish to have much of the experience of a 718 Spyder or 718 Cayman GT4 with perhaps less emphasis on track performance.”
Put your engineering caps on, because we’re going to take a deep dive into Porsche’s 4.0-litre flat-six engine, see what makes it so efficient, why it doesn’t need turbos, and how it behaves when we rev it up to the stratosphere in the new 2021 Porsche 718 Boxster GTS 4.0.
Forget natural aspiration for a second and take a look at the shape of this engine. Notice anything different from a V6 or inline-six? The cylinders are firing from side to side, rather than up and down or in a V shape. That is what gives Porsche’s army of flat-six engines their distinctive look, noise, and power delivery - it’s also why their flat four-cylinder sounds like a Subaru WRX, which also uses the same “Boxer” layout. That arrangement comes with its own advantages such as being inherently balanced with fewer mechanical vibrations, compact enough to be suitable for mid-engine applications, and having a low center of gravity.
But where did this engine come from? Did Porsche develop a whole new engine from scratch for their two weakest selling sports cars? Not quite. We first saw this engine inside the 2018 718 Cayman GT4 and 718 Spyder (982), and it has been detuned for the 718 GTS 4.0 application. In truth, it’s actually a bored and stroked version of the 3.0L 9A2 twin-turbo flat-six we piloted in the 911 Carrera (992), sans the two turbochargers. No, it has nothing to do with the outgoing 911 GT3’s 4.0-litre engine, as it doesn’t fit in the mid-engined Boxster.
This 24-valve, DOHC, flat-six engine uses an aluminum block and heads, direct fuel injection, forged pistons, and plasma-coated cylinders. There are 4 valves per cylinder, integrated dry sump lubrication, and is water-cooled as well. To ensure some semblance of efficiency, Porsche has even integrated cylinder deactivation, the first flat-six to do so. That means under light power loads, it will shut off three of its cylinders to save fuel and boost emissions. There is start stop technology as well. We ourselves averaged 12.5 L/100km with a mix of both city and highway driving, not bad for a lightweight sports car begging to be driven hard.
So what kind of power is it packing? Without forced induction, the output may seem low on paper. The 4.0L delivers 394 hp and 317 lb-ft of torque, and just 309 lb-ft when equipped with the manual transmission. In comparison, the 2.5-litre turbo-four in the Boxster S produces a comparative 350 hp and 309 lb-ft. Horsepower in the 4.0L peaks at 7,000 rpm, while maximum torque is reached at 5,500 rpm, much higher in the powerband than the 2.5L. As a result, the 4.0 needs to be wrung out and worked hard to reap the rewards. Rev it high, kiss the 7,800 rpm limiter, and just remember that the faster you go, the more alive it feels.
The numbers may not sound competitive versus the Jaguar F-Type R and BMW M2 CS, both of which harbour in excess of 400 horsepower, but the Boxster GTS is significantly lighter, with a proven dual-clutch transmission that fires it from 0-100 km/h in a scant 4.0 seconds. No, it’s not as scintillatingly quick as a Nissan GT-R, and it doesn’t reach the same stratospheric 9,000 rpm redline as the 911 GT3, but the accessibility and exploitability of its output means that it never feels penalized by the lack of forced induction. You can use every horse in its stable, and be met by traction and surefootedness that only a mid-engined setup could provide.
The linearity in power delivery shouldn’t go unnoticed either, as it’s something that most drivers can appreciate but are rarely offered. To add to driver engagement, buyers have the choice between a manual transmission and a 7-speed dual-clutch PDK gearbox, the latter of which was on our test vehicle. While we prefer to row the gears ourselves, we can’t deny the sharp wits of the PDK and its lightning quick shifts, helping us to fully exploit the seven available gears.
The acoustics are rewarding, especially when you lower the Boxster’s electrically-operated roof, giving you front row seats to one of the best automotive orchestras in town. Whereas more and more automakers are turning to turbochargers that sedate the exhaust noise, this GTS 4.0 is a breath of fresh air, both literally and figuratively. With a voice that breathes atmospheric pressure unencumbered by messy internal plumbing, it’s able to produce orchestral, sonically pleasing notes that stimulate the ears, mind, and soul. This soundtrack is central to the engine’s beauty and while not as iconic as the V10 from the Porsche Carrera GT or the flat-12 from the Porsche 917K, it hits melodic frequencies that we rarely hear in today’s sports cars.
There are three stages of noise, as the engine uses a variable intake manifold with two switchable resonance valves that are slightly open between 3,000-5,000 rpm, and fully open past that. Unsurprisingly then, the best sounds are found at 5,000 rpm and when cresting the 7,800 rpm limiter. It’s 200 rpm shy of the Spyder’s 8,000 rpm redline, but we hardly notice the difference. We adore the rich noise of any flat-six, as they remind us of free breathing 911s from the past, cars that sounded as good as they handled.
Granted, there seems to be more intake noise radiating through the bulkhead than actual exhaust noise, and it’s rather quiet and subdued when cruising in the left half of the tachometer. The evocative noise is further correlated with how deep the throttle is pressed. Explore the latter half of the pedal and the volume grows exponentially, delivering a mildly scaled-down form of the 911 GT3’s spine-tingling orchestra. The one issue however is the tall gearing, meaning by the time you hit the limiter in second gear, you’re already reaching 120 km/h. So you’re either speeding, or you’re speeding.
Comparing this 4.0L screamer to the prosaic 2.5L was never going to be a fair fight, as the addition of two extra cylinders brings a much needed personality to the 718 family. It trades easy low-end torque for rewarding high-end theatrics, and we prefer the latter. There really is no replacement for displacement. But that’s not the case with every 4.0L. You see, European-spec GTS models are equipped with particulate filters on each cylinder bank, meaning its exhaust fumes and funneled through filters that result in cleaner emissions. Canadian-spec models on the other hand are under less stringent regulations, and use a more conventional filter that chokes up less of the exhaust noise.
Just when we thought emission regulations, small displacement engines, and electric vehicles were beginning to sweep automotive personalities away, along comes Porsche with a naturally aspirated 4.0-litre engine that sweetens the honey pot with spellbinding acoustics and linear power delivery. After spending a week with the 718 Boxster GTS 4.0, we can report that it’s an engineering masterpiece that fires with all the richness and high-timbred tonality that you would expect from a race bred engine. Cleverly blending both mechanical and electrical brilliance into a melting pot of fuel and oxygen, this motor not only delivers a sense of nostalgia, but it brings us back to a time when free breathing engines reigned supreme. Do we see a bright future for this 4.0L? Unfortunately not. We expect the next-generation 718 to be either hybrid or fully electric. Sad, but inevitable. Here’s to the good times.
Model: 2021 Porsche 718 Boxster GTS 4.0
Paint Type: GT Silver Metallic
Base Price: $96,900
Price as Tested: $117,800
Length/Width/Height (mm): 4,391 / 1,801 / 1,262
Engine: 4.0-litre flat six-cylinder
Horsepower: 394 hp @ 7,000 rpm
Torque: 317 lb-ft @ 5,500 rpm
Transmission: 7-speed dual-clutch automatic (PDK)
Engine & Drive Configuration: Mid-engine, RWD
Observed Fuel Consumption (L/100km): 12.5
Tires: Michelin Pilot Sport 4S