When it comes to the pure mechanical symphony of an engine, nothing can ever replace the purity of a naturally aspirated engine. Especially when it comes to a well-balanced, smooth, and high-revving one. This is the reason people have loved the Porsche flat six for a very long time. This has been the engine that has powered the legendary 911 since 1964 and has undergone various updates and changes since then, but still powers this iconic sports car without giving up its iconic engine note. But the quest for more power, better fuel economy, and emissions is forcing this pure masterpiece to take a different path.Turbos used to be reserved for the most special 911s, but these days every 911 has a turbo, and a more mechanical engine is reserved for the very special cars. So, before the iconic Porsche flat-six will be phased out like many other great engines, we would like to celebrate the best applications of the various engines before they're gone for good. Porsche 964 Carrera - 247 HP 3.6-liter Flat-Six Bring a TrailerThe 964 has become one of the most valuable 911 models in history and one of the most important. It featured the M64 3.6-liter flat-six engine that originally made 247 horsepower and 228 lb-ft of torque. This was the first road-going Porsche engine to feature twin-spark ignition and a resonant intake system, which worked together to make power efficient across a broader power band. But it also made the car sound perfect all the way to its 6,700 rpm redline. It was also the first 911 to get a four-wheel drive variant known as the Carrera 4; this setup was derived from the Porsche 959.Bring a TrailerWhile these cars have long stopped production, they have found new life in the resto mod scene as companies like Singer Vehicle Design have made it a mission to make the best version of these cars. But that also means these cars are in demand and are pretty expensive. An average 964 Carrera 2 now costs $102,000, which means the special variants cost a lot more. But to those who can afford the stock cars or the absurdly expensive but enhanced and perfected restomods, the price is worth it since they get to enjoy an experience that turbo cars can never replicate. Porsche 993 Carrera RS - 300 HP 3.8-liter Flat-Six Bring A TrailerThe US never officially got the RS version of the 964, but the demand was there, so for the 993, we got one. This was another important 911 as it was the last generation to get the air-cooled flat-six engine. The Carrera RS was the lightweight version of the 993 Carrera, which had a larger and more powerful 3.8-liter flat-six that made 300 horsepower and 262 pound-feet of torque. It also featured Porsche's innovative VarioRam intake system that delivered an intoxicating mechanical wail as it chased its 6,500 rpm redline.Bring A TrailerAs the final, most hardcore evolution of the air-cooled 911, the 993 RS sits firmly in the seven-figure blue-chip collector territory. If you want one, the average price is $344,000. To the enthusiasts, this car is the holy grail of 911s. This was a car that promised weight savings above all else, which allowed the raw, mechanical sound to fill the cabin completely unmuted. Porsche Boxster Spyder (981) - 375 HP 3.8-Liter Flat-Six NetCarShowThe Porsche Boxster was always second choice to the 911 but the 981 Boxster Spyder broke traditional hierarchy by borrowing the 3.8-liter naturally aspirated flat-six from the 911 Carrera S. But instead of being in the back of a 911, it was dropped into a lightweight, mid-engine convertible with 375 horsepower and 310 pound-feet of torque and a six-speed manual gearbox only, for complete engagement with the car. This was basically the convertible version of the original Cayman GT4, and with a 7,800 rpm redline, the Boxster was just as enjoyable as any 911.Porsche The 981 Spyder has managed to carve out a permanent niche as a modern classic already, holding its value far better than its standard production cars. The recipe of a balanced mid-engine setup, a large 911 engine, and a manual convertible gave drivers a unique experience almost no 911 had offered. Porsche 996 GT3 - 381 HP Early 3.6-liter Mezger Flat-Six Bring A TrailerPurists panicked when they heard the new 911 would be water-cooled but the 996 GT3 proved it was worth it. This was the start of the beloved Mezger flat-six, which was a 3.6-liter motorsport-derived engine originally making 360 horsepower and 273 pound-feet of torque. The later 996.2 made 381 horsepower and 284 pound-feet of torque, sending all power to the rear wheels via a six-speed manual. While this car drove and sounded great, it had a very obvious problem.PorscheThe styling was controversial, but as people have looked past that, the values have shot up. It offers a very analog experience as it has no traction control, a cable-driven throttle, and demands total concentration. This car proved water-cooled engines could still deliver an exhilarating experience, setting the template for every modern GT car that followed. Porsche 718 Cayman GT4 RS - 493 HP 4.0-liter Flat-Six Bring A TrailerThe 718 GT4 RS followed the path of the Cayman GT4 but instead of getting the Carrera engine, it got the full-fledged 4.0-liter, 9,000 rpm engine straight out of the 911 GT3. Porsche finally allowed the mid-engine Cayman to use the big-boy engine, but in this application it made 493 horsepower and 331 pound-feet of torque. But Porsche didn't just give it the GT3's engine; it focused on creating a sensory experience no 911 has offered.Porsche This masterpiece of engineering had a carbon fiber airbox placed directly inside the cabin where the rear quarter windows used to be. The resulting induction sound behind your ears is a ferocious, metallic assault on the senses that turbo spools can never achieve. These features instantly gave the GT4 RS collector status as the first RS model in the Cayman lineup and commanded premiums in the new and used collector market. Porsche 997 GT3 RS - 500 HP 4.0-liter Mezger Flat-Six Bring A TrailerThe 997 GT3 RS 4.0 is widely regarded as the absolute zenith of the manual, water-cooled Mezger era. This engine used the crankshaft from the 911 RSR race car, and Porsche bored the original GT3 from 3.8 liters to 4.0 liters. This car was now making 500 horsepower and 339 pound-feet of torque, sending power to the rear wheels via a six-speed manual transmission. Only 600 units were built worldwide, turning this car into an instant legend with values climbing steadily towards the half-million-dollar mark.Porsche This car is widely considered the best 911 of all time by all Porsche enthusiasts, especially from a driving and engagement standpoint. It was the absolute limit of what a road-legal, motorsport-derived, naturally aspirated Mezger engine could achieve before the brand moved away from this engine and also transitioned to electronic steering and dual-clutch-only platforms. Porsche 911 R - 500 HP 4.0-liter Flat-Six Bring A TrailerThe 911 R was Porsche's love letter to its beloved 911. When the 991 GT3 and GT3 RS first came along, no manual option was offered and in 2016 this was born. The limited-run 911 R used the 4.0-liter flat-six engine from the GT3 RS but with lighter parts and faster revs. It produced 500 horsepower and 338 pound-feet of torque. It was also paired exclusively with a bespoke six-speed manual transmission. This was the ultimate drivers' 911 with no intention of chasing lap times at all but prioritizing ultimate driver engagement.The 911 R reached instant collector status at launch because everyone thought this was the final manual 911 Porsche would ever make. So values spiked above a million dollars on the used market before settling in the $300,000 to $500,000 range, which is still well above its $185,000 MSRP. The 911 R is historically significant because it forced Porsche to listen to its core audience and give them exactly what they wanted. It proved that driver engagement, mechanical feedback, and the simple joy of a manual gearbox mattered far more to enthusiasts than raw lap times, and Porsche has repeated that formula ever since. Porsche 911 GT3 Manual (991.2) - 500 HP 4.0-liter Flat-Six Bring A TrailerThe 991.2 GT3 finally got the same 4.0-liter flat-six engine used in the 991.1 GT3 RS. The 4.0-liter, 9,000 rpm masterpiece still made 500 horsepower and 339 pound-feet of torque but made improvements by utilizing a rigid valve train derived directly from Porsche's Mobil 1 Supercup race cars.Porsche After seeing the huge demand for a manual transmission, Porsche made it available for this updated GT3. Values have also remained quite strong, as Porsche seems to be the only manufacturer that still listens to its audience and offers engaging manual cars like these. You can run impressive laps if you get the PDK option, but even with a manual, you can still set very close times and enjoy yourself doing it. Tuthill 911K - 350 HP 3.1-liter Flat-Six TuthillThe Tuthill 911K is not just another restmod 911, but it may well be the ultimate expression of the naturally aspirated flat-six. It features a bespoke 3.1-liter short-stroke engine that revs to an astonishing motorcycle-like 11,000 rpm, producing around 350 horsepower in a car that weighs a mere 1,874 pounds. Tuthill's background is in rally racing, so the car has been set up to reward driving at high rpm with the magnesium six-speed manual transmission.Tuthill Only 33 of these cars were built for the world's most discerning enthusiasts, the 911K exists in a stratosphere beyond normal market trends. It is a celebration of mechanical art and highlights the fact that the passion for the naturally aspirated flat-six isn't just surviving but is thriving in a world that is being taken over by turbos and electrics, and is actively being reinvented by brilliant engineers who refuse to let the pure mechanical connection die.Sources: Porsche, Tuthill, Hagerty, Classic.com.