Most would agree that the Porsche 911 GT3’s 4.0-liter flat-six naturally-aspirated unit is one of the best driver’s engines available today, letting the tachometer needle touch the 9,000 mark and providing incredibly responsive and linear power delivery.
And then there is the sound, starting from a low-frequency roar and developing into a high-pitched angry ring that’s music to anyone’s ears. Blip the throttle on a downshift, and the quick rev jump will literally tickle your senses. It’s a symphony that never gets old and one that you can enjoy gear after gear.
But the 4.0-liter also boasts turbo-rivaling horsepower numbers (520 hp in the latest 991.2 GT3 RS) and excellent torque figures. Never before has a naturally-aspirated engine been so capable at low revs while also providing a 9,000 rpm redline.
It’s a pure driving joy, this engine.
Other manufacturers tried and failed to perfect the naturally-aspirated formula (even Ferrari went full turbo) for the 2020s. However, Porsche is famous for its engineering prowess and the ability to succeed where others fail. And, without any exaggeration, the 4.0-liter flat-six is an automotive masterpiece, lifting the already fantastic 911 GT3 and 718 Cayman GT4 to an almost mythical level.
But how did Porsche extract that much power from a naturally-aspirated unit and make it work with current pollution regulations? Let’s have a closer look at this engineering jewel and see what makes it that special.
Read more: Porsche 996 911 GT3 — The Dawn of the Perfect Driver’s Car
Which Porsche Cars Use the 4.0-Liter Flat-Six?
To better understand what makes these engines so unique, we first need to examine the cars that use them. Porsche is part of the much larger Volkswagen Group, famous for its part-sharing habit, which effectively means that cars from different brands may have identical mechanical assemblies under their skin. For example, some Porsche Macans use the same engine as a Golf GTI, while the larger Cayenne shares its drivetrain with the Audi Q7. Such a manufacturing approach allows them to utilize existing resources more efficiently and lower production costs.
Fortunately, Porsches’ flat-six engine is not concerned here, as its application is only limited to their track-focused sports cars. And the actual engine in question here is only available in particular 911 and 718 Cayman models. And, by “particular,” we mean the GT3 and GT4, their angrier RS versions, and the one-off 911 R (a detuned version of the engine is also used in the GTS versions of the 911 and 718 Cayman/Spyder models).
No need to mention that these are no standard Porsche sports cars — every other model in the brand’s lineup now employs turbocharged flat-four engines. Moreover, the GT3 and GT4 also feature track-ready suspension upgrades, ultra-stiff, and lightweight bodies, upgraded brakes, better aero, etc… Basically, everything they need to be super-quick around any track while putting a big grin on the driver’s face.
Advantages of Flat or “Boxer” Engines
The drivetrain layout is just one of the things that make the 911 so unique, as its engine is quite different as well. Despite their differences, almost all modern engines use one of the two most common configurations: in-line or in a “V” configuration. Most smaller and mid-sized engines use an in-line shape, with all cylinders lined up in a single row, while most larger engines are divided into two cylinder banks and positioned at an angle (hence the “V” nomenclature).
Flat-six (boxer) engines also have two separate cylinder banks of three pistons each. But unlike in a V-engine, the banks here are opposed to each other. Such a configuration offers several benefits, including exceptional rotational balance and a lower center of gravity, helping to reduce body roll while cornering and significantly improving handling. With an experienced driver behind the wheel, the Porsche 911 becomes a sharp tool, precisely cutting through any corner.
Interestingly, while these engines received many upgrades and modifications through the years, including going from air to water cooling, their basic layout remained the same, becoming one of the 911, 718 Cayman/Spyder, and Boxster’s signature marks.
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What Makes the Porsche 4.0-liter Flat-Six an Engineering Marvel
Porsche’s first 4.0-liter flat-six was introduced in 2011 in the then-current 911 GT3 RS as the most powerful naturally-aspirated engine in the lineup. It was, however, much more than just a slightly bigger unit than its predecessors. During the development phase, engineers used many internal components from their racing engines, such as crankshafts or conrods. Once paired with several other mechanical trickeries, the changes allowed the new engine to rev up to 9,000 rpm safely in some versions. Moreover, intake manifolds and the fuel injection system went through a thorough redesign, ensuring they could keep up the pace.
But let’s get into more nerdy details!
All about that intake
Naturally-aspirated engines have the downside of sucking up air at atmospheric pressure, as opposed to turbocharged engines, which can compress the air and send a higher volume of oxygen into the combustion chambers, allowing them to burn more fuel and ultimately create more power.
Still, thanks to proper engineering, some modern naturally-aspirated engines can actually increase the air pressure inside the cylinder; for engines like the Porsche 4.0-liter flat-six, the air pressure inside the cylinder would be 15-20% higher than the current atmospheric value —not turbo-level, but impressive nonetheless.
And the intake is crucial to give that boost in pressure (using some turbo jargon, eh!). Thus, Porsche equipped its most advanced engine with a variable intake manifold with two resonance valves/butterflies connecting the two cylinder banks. These valves can redirect the low-pressure waves from one cylinder (created when the intake valve opens) back into the combustion chamber of another one, along with the atmospheric air, increasing pressure above the “standard” N/A threshold.
There is a problem here, though — the system requires clever use of the resonant waves, as they can also be detrimental to creating more pressure at some engine speeds. Thus, the ECU controls the intake valves (via Variable Valve Timing) and resonance valves to create the highest amount of power at every rpm; for instance, at lower rpm, both resonance valves would be closed, then at mid-rpm, one would open, and at high rpm, both would open. It’s like using musical waves to create more pressure — no wonder the 4.0-liter sounds that good!
But there is another piece to this puzzle, and it’s directly borrowed from racing engines — an individual throttle body for each cylinder. Yup, that’s six individual throttle bodies right there!
As a result of all these advancements, Porsche engineers have complete control of the intake process.
Maximum responsiveness and high-rpm zing
The Porsche 4.0-liter flat-six engine has an extremely short stroke (81.5 mm) and a very wide bore (102 mm). As such, the pistons can achieve very high speeds with relative ease, but crucially, the intake valves are also much larger than in a narrow-bore engine. And as discussed above, the intake airflow is vital in naturally-aspirated engines, as they need as much air as they can get.
Furthermore, the pistons are forged for lower weight and better durability, while the cylinders are plasma-coated to reduce friction. Consequently, the pistons can move more freely inside the cylinder, ensuring maximum responsiveness and providing an exhilarating 9,000 rpm redline!
Valvetrain with old-school shims
Modern engines use hydraulic valve lifters, eliminating the need for periodic valve adjustments. However, hydraulic lifters are also slower and can limit the maximum rpm an engine can attain. Hence, Porsche went with old-school shims instead, sitting between the cam and the rocker arms, ensuring revolutions of up to 9,500 per minute in racing versions of the engine.
But does that means Porsche GT3 and GT4 owners will then need to readjust the valves occasionally? Wrong (duh) — Porsche used carbon coating on the rocker arms, creating a surface as hard as a diamond. Hence, the valve clearance will stay the same for the engine’s lifetime!
Dry-sump lubrication system
Dry-sump lubrication isn’t a revolutionary idea, but it’s crucial for an engine that will spend most of its lifetime experiencing high G’s on a racetrack. What makes Porsche’s oil distribution system innovative is the use of seven scavenge pumps to redistribute oil across the engine, ensuring that every part is properly lubricated at all times. The system is so powerful that it circulates 6.4 liters of oil inside the engine without a problem. However, Porsche never satisfied with just “good enough,” went a step further and used a race-derived centrifuge to separate the air from the oil, improving the lubrication film left on the components.
Forged crankshaft
Porsche’s 4.0-liter flat-six is so furious that it creates quite a load on the crankshaft. Luckily, as money was clearly no object here, Porsche went with a forged crankshaft made from high-strength steel alloy, accompanied by larger journal bearings. Moreover, the company used lightweight and stiff titanium connecting rods, ensuring the whole setup could withstand that 9,000 rpm figure.
Impressive Numbers for a Naturally-Aspirated Engine
All those advanced materials and clever engineering result in 520 hp @ 8,250 rpm and 346 lb-ft of torque @ 6,000 rpm (in the 991.2 GT3 RS). Remember, the engine has a 3,996 cm3 displacement, equating to 130 hp per liter — quite exceptional for a naturally-aspirated engine.
Still, these numbers only tell half of the story since how all that power is actually delivered is another of its upsides. Indeed, thanks to the atmospheric configuration, there is absolutely no turbo-lag, so the throttle response is sharper, making for smoother and more predictable accelerations in dynamic driving conditions. With this engine, barely touching the gas pedal produces an immediate reaction — crucial when you want to precision-attack every corner.
Read more: Porsche 718 Cayman GT4 RS – Gifted with the Perfect Heart Transplant
The Cars Also Help the 4.0-liter Flat-Six Deliver Astonishing Performances
Porsche’s power unit engineers spent so much R&D effort to create the lightest components, so it was only fitting that their chassis/body counterparts did the same. After all, naturally-aspirated engines aren’t very good at lugging a lot of weight around — that’s an area where turbocharged units excel.
Therefore, the GT3 and GT4, and particularly their RS variants, are the lightest models in the 911 and 718 Cayman ranges. Obviously, achieving something like that is only possible with some serious weight reduction programs. For instance, the door handles and roof are made from lightweight magnesium, the door windows are thinner, and the backglass is made of plastic. Porsche went to such lengths to shave off the extra weight that it even used vinyl stickers for the hood badge.
Thanks to such a rather drastic diet, the GT3 RS and GT4 RS provide an immediate steering response, turning ferociously into a corner with even the slightest steering input. They are also super-fast; the 911 GT3 RS needs only 3 seconds to touch the 60 mph mark, while the 718 Cayman-based GT4 RS makes the same ubiquitous sprint in just 3.4 seconds, both reaching their top speed of around 195 mph.
Of course, chassis and suspension upgrades also help to improve high-speed handling. The RS models’ shock absorbers are adjustable in ride height and dumping rate, ensuring the right balance for every road and surface. In addition, four-wheel steering improves maneuvering through high-speed corners (GT3 RS) and helps keep the rear end tightly locked. Lastly, a roll cage, fitted instead of the rear seats, helps stiffen up the chassis. These upgrades provide the GT3 RS and GT4 RS with superior grip and make them incredibly stable when pushing the limit.
Last Words
It’s safe to say that if you reached this point of the article, you were already in love with Porsche’s 4.0-liter flat-six. And I hear you; heck, I’ve never even tried a Porsche GT model, but the sheer prowess of the engine in terms of engineering, performance, and sound was already more than enough to make me dream about it.
Besides, with all those EVs on the horizon, masterpieces like this naturally-aspirated marvel won’t see showrooms again soon (well, maybe if we were to somehow discover that burning dinosaur juice was in any way good for the environment? But it’s not). So, being sympathetic to such a powertrain is almost a prerequisite, right?
But let’s hope for the best! Porsche recently launched the GT4 RS, a mid-engined sports car using the 4.0-liter flat-six, and didn’t mention anything about it being the last model. Regardless, for those lucky “f$w” that already ordered it, the GT4 RS will give them the ride of a lifetime, just like every other Porsche GT car before.
Oh, and as a bonus for us, ordinary people who will probably never have the chance to sit in one, let alone drive one around a track, here’s a pretty cool video!
Just. Listen. To. That. Sound.
Pure poetry — here, soundwaves prove a point that words can only dream of describing.
