The Most Powerful Naturally Aspirated Six-Cylinder Ever Produced

Whether you are a tuner or a manufacturer, there comes a time when that turbocharger sitting on the shelf becomes too hard to resist. Ultimately, it becomes more and more difficult to squeeze extra power out of an engine before resorting to forced induction, courtesy of a supercharger or turbocharger. Then the gains become plentiful and allow engines such as this 1.6-liter three-cylinder to produce 304 horsepower. Sticking with atmospheric pressure for an engine means going for a large displacement, screaming rev limits, or both.

While supercars and hypercars can rely on large, naturally aspirated V12s to create formidable performance, there is one manufacturer that is still creating an ultra-high-performance model that makes do with just six cylinders. This iconic model may be devoid of turbos or superchargers, but its horsepower rating is higher than in many boosted production sixes. In fact, it makes almost 8 hp more per liter of displacement than the incredible LT6 V8 in the Corvette C8 Z06, which is the most powerful naturally aspirated V8 engine ever made. This is a sports car that has evolved over many years into this current state of automotive genius.

Honda S2000 Engine

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The Porsche 911 GT3 RS Has The Most Powerful Naturally Aspirated Six-Cylinder Engine

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Porsche 911 GT3 RS Highlights

• Its 4.0-liter naturally-aspirated flat-six produces 518 horsepower and 342 lb-ft of torque
• The Porsche 911 GT3 RS will hit 60 mph in 3.0 seconds and a top speed of 184 mph
• It revs up to a stratospheric 9,000 rpm

Let's get one thing straight, the 2025 Porsche 911 GT3 RS is not the kind of car you use if being low-key is high on the agenda. The GT3 RS may be road-legal, but it looks like it has just pulled in from a hot lap at the Circuit de La Sarthe. The giant wing, the vents, the strange aero protrusions, all help to make the GT3 RS look like a legit race car. No wonder then, that the clever lightweight construction and the cooling and aerodynamic systems of the 911 GT3 RS have their roots in the road car's motorsport sibling, the 911 GT3 R.

The 911 GT3 Rs's Engine Has Racing DNA

Another component with racing DNA is the engine. The high-revving 4.0-liter naturally-aspirated mill now has 518 horsepower and 342 lb-ft of torque – making it the most powerful of its kind in the world. This flat-six will rev all the way to 9,000 rpm and is mated to a seven-speed Porsche Doppelkupplung (PDK gearbox) that has a shorter overall gear ratio than the 911 GT3.

This gearbox also benefits from some trick aero, with air intakes on the underbody that help it perform under extreme loads during a particularly committed track day. The Porsche 911 GT3's flat-six takes the car to 60mph in 3.0 seconds (0.2 seconds quicker than the standard GT3) and the top speed is 184 mph in seventh gear.

V6

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A Closer Look At The Porsche 911 GT3 RS's Spectacular Engine

Porsche

2025 Porsche 911 GT3 RS Specs

Source: Porsche

The 4.0-liter naturally aspirated six-cylinder engine is an evolution of the 911 GT3's powerplant but has been seriously reworked. When it comes to an already optimized unit, that increase of just 16 horsepower takes a lot of work. Porsche's engineers have added new camshafts with modified cam profiles, as well as a single-throttle intake system and a rigid valvetrain, both developed from the company's motorsport program. The same as in the 911 GT3, the engine has six individual throttle bodies, meaning one for each cylinder. This DOHC 24-valve flat-6 also features aluminum block and heads, and direct fuel injection.

The Radiator Set-Up Comes Straight From The Race Track

The Le Mans class-winning 911 RSR and the 911 GT3 R have a very special detail in common: a central radiator. It might sound a bit humdrum, but the large, angled central radiator in the GT3 RS's nose, where the bags would normally go, is a game-changer. Earlier cars had three radiators, which make it difficult to integrate active aerodynamic elements on the sides.

The 911 GT3 RS features continuously adjustable wing elements in the front and on the two-part rear wing, helping to provide more than 900 lbs of downforce at approximately 124 mph - three times as much as a current 911 GT3. Hitting 177 mph creates a total downforce that is 1,895 lbs, or roughly the same as a Mk1 Volkswagen Golf.

There Was A British Manufacturer That Wasn't Far Off The Porsche...20 Years Ago

Collecting Cars

2005 TVR Sagaris Specs

Source: TVR

While the GT3 RS's naturally aspirated flat-six is impressive, it's worth looking back a couple of decades to a company that was also creating big power without turbochargers. TVR was a British company that essentially hand-built monster sports cars out of a few sheds near a seaside resort. But don't let that fool you – TVRs were some of the meanest cars in the business. While TVRs were famous for using V8s in the past, it is arguably the company's Speed Six engine that really put it on the map.

The Speed Six is a torquey, naturally aspirated powerhouse with an incredible 400 horsepower and 349 lb-ft in models such as the Sagaris. This aluminum straight-six engine is extremely light and set so far back in the car that it earned a front/ mid-engined designation. The rear-drive Sagaris can hit 60mph in 3.8 seconds, and a frankly terrifying top speed of 195 mph.

Getting The Keys To A GT3 RS

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Porsche 911 GT3 RS Prices

• New price: From $241,300
• 2023 Used Price: $400,959
• 2024 Used Price: $407,804

Source: Classic.com/ Porsche

A Porsche 911 GT3 RS isn't cheap - but you probably already guessed that. Buying one new will cost at least $241,300, and that's before you add on things like the Weissach package, which includes a visible carbon fiber hood, roof, and parts of the rear wing, as well as clicky PDK shift paddles with motorsport-derived magnet technology. The used market isn't exactly filled with bargain GT3 RSs, either.

Classic.com says the average price of the 2023 Porsche 911 GT3 RS is an astonishing $400,959, whereas the 2024 model year goes up to $407,804. It's not surprising the average price even of used models is so high, with many Weissach package-equipped cars commanding almost $400,000 on the used market. We found this wild-looking 2024 Porsche 911 GT3 RS Weissach that sold for $378,000 in 2025. If that's a little out of your price range, try shopping for one of Porsche's most underrated models instead.