The Greatest Straight/Inline 6 Engines Ever Produced. Internally combustion engines have existed in a variety of configurations since the early nineteenth century. Internal combustion engines have come in many forms and sizes, from Carl Benz’s 0.75 horsepower, one-cylinder engine that drove the world’s first automobile to the 860 horsepower Ferrari V12s at the back of Formula One cars in the 1980s.
One engine type stands out due to its unusual placement in a wide range of iconic sportscars. The inline 6 engine was presented to the world in 1903, a few years before the V6 engine was used in a vehicle. Because of the design issues that come with such a long engine, the inline 6 engine arrangement is possibly less popular in modern automobiles. Yet, inline 6 engines offer several unique benefits to V6 engines. As a result, despite its declining popularity, certain manufacturers, such as BMW, have chosen to stay with the inline 6 design.
With the internal combustion engine nearing the end of its useful life, it’s interesting to consider that the best inline 6 engines have already been built. In this article, we will discuss the inline 6 engines that have had a significant impact on the automobile market and define the category as a whole.
What Exactly Is An Inline 6 Engine?
Internal combustion engines are generally classified into two types. Inline engines and V engines are examples of these two categories. There are other types of engines, such as flat, boxer, and W engines, but they are less popular than the two stated above. While both inline and V engines produce power in virtually identical ways, their designs are vastly different.
Inline (or straight) engines are far less sophisticated than V engines. As the name implies, all of the engine’s cylinders are lined up in a single row along the crankshaft. It suggests there is only one cylinder bank. A straight 6-cylinder engine has a single-cylinder head, head gasket, and valvetrain. As a result, straight 6 engines are not only simpler, but also easier to work on.
Because there is only one bank of cylinders, the straight 6 design has a variety of distinct properties. Inline six engines, for example, are much slimmer and longer than V6 engines. Straight 6 engines require larger camshafts to operate the single valvetrain due to their higher length.
In comparison to other engine configurations that require counterweights and other procedures to achieve good engine balance, such as inline 4 cylinders and V6 engines, inline 6s with the proper firing order are among the most balanced engines available. This results in incredibly smooth engine operation and power delivery.
The Advantages and Disadvantages of Inline 6 Engines
The inline 6 engine design, like every other engine type, has advantages and disadvantages. Many of the advantages of the inline 6 design stem from the fact that there is only one bank of cylinders. Because an inline 6 engine has fewer components to work, there is less that may potentially go wrong. That also means they are easy to service because everything is accessible from one side of the engine room.
While we briefly said that inline 6 engines are more balanced than many other engine layouts, it is critical to understand why. It all comes down to firing sequence. Pistons move in unison with their counterparts on the opposite side of the engine in a typical inline 6 firing order. This design extends into the center two cylinders.
To elaborate, pistons 1 and 6 finish their cycles simultaneously, followed by pistons 2 and 5, and finally pistons 3 and 4. Because the pistons at opposing ends of the engine are moving at the same time, their forces cancel each other out. This results in a very smooth engine with no vibration.
While inline 6 engines have several significant advantages, they also have certain disadvantages. The majority of the disadvantages are related to the engine’s overall length. Straight 6s are difficult to fit in smaller vehicles because they stretch so far back towards the firewall. Furthermore, the increased length of several internal components, such as the extra long camshafts, causes higher flex, making them more susceptible to breaking under stress.
The Nissan RB25DET
For many automotive fans, the first entry on this list is self-explanatory. It is not just one of the best inline six engines, but it is also arguably one of the best engines ever built. It is also seen in one of the most famous Japanese automobiles of all time. To say the least, the Nissan RB25DET has a lot going for it.
The RB engine series became well-known due to its use in the Nissan Skyline. The 2.0L RB20DET was the factory engine in many of Nissan’s flagship sportscars prior to the RB25DET. The RB25DET added 0.5L of displacement as well as other significant breakthroughs in engine technology. In 1993, the RB25DET was first spotted in the engine bay of the Nissan R33 GTST. Its most prominent applications include the R33 GTST, R34 GTST, Nissan Stagea, and Nissan Laurel, to name a few.
Aside from being used to power some of Japan’s most iconic vehicles, the RB25DET is also a tremendously powerful engine with a lot of power potential left untapped by the factory. The inline 6 RB25DET produces between 245 and 280 horsepower in stock condition, depending on the type. In actuality, its power figures are likely to be higher than those stated by Nissan.
Nissan RB25DET Engine Specifications
Because of its cast iron/aluminum head composition, the RB25DET is a very strong engine right out of the box. When combined with larger injectors, stronger injectors and connecting rods, and a larger turbocharger than the previous RB20DET, the RB25DET is a true force to be reckoned with.
Between 1993 and 2001, the RB25DET saw several upgrades. The Series 2 RB25DET was the first modification, with minor adjustments to the electrical system and the switch to a ceramic wheel turbocharger. Another, more substantial upgrade arrived in 1998 with the release of the RB25DET NEO, which saw a significant performance gain over the Series 2. The RB25DET NEO received a new head with solid lifters, updated camshafts, and variable valve timing, resulting in an additional 30 horsepower and torque.
Toyota 2JZ-GTE engine
The Toyota 2JZ-GTE engine has the same legendary reputation as the RB25DET engine that we previously discussed. The Toyota 2J, as it is generally known, is the engine that established the MKIV Supra as one of the best sports cars ever built. In the mid-1990s, while the Nissan Skyline and Toyota Supra competed for street supremacy, the straight-6 engines that powered them were also put to the test.
The Toyota 2JZ-GTE engine is a 3.0L twin-turbo DOHC engine that was introduced in 1991. While producing 320 horsepower from the factory, like the RB25DET, the 2JZ is noted for its incredible tuning capability. There are 2JZ-GTE engines out there that can produce 1,000 horsepower with minimal to no internal changes. That is the true strength of the cast iron block, forged rods, and forged camshaft. The 3.0L 2JZ-GTE was also one of the first modern mass-produced engines to include sequential turbochargers, which spooled at varying intervals throughout the rpm range. This means that lower-end boost from one turbo flows into higher-end boost from the secondary turbo, resulting in less visible latency.
The 2JZ-GTE genuinely flourishes in the aftermarket world, where nearly anything that can be done to a 2JZ-GTE has been done. With so much part availability and modding information available, you may achieve any power target with the 2JZ platform. Straightforward 2JZ-GTE bolt-ons can push the engine to 400 horsepower. Even more intensive modifications, like as improved turbos, can push a 2JZ-GTE into the 600-800 horsepower range.
The 2JZ-GTE will undoubtedly be remembered as one of, if not the, best inline 6 engines ever built. The 2J’s strength, aftermarket support, and cult fandom combine to make it a difficult engine to surpass.
Toyota 2JZ-GTE Engine Specifications
The 2JZ-GTE is a bulldog when it comes to managing power, as it is a closed deck engine with a cast iron block and several forged internals. This is exacerbated by its comparatively low 8.5:1 compression ratio, which means it can tolerate significant boost. The 2JZ-GTE has a square engine due to its similar stroke and bore. Square engines are well balanced in terms of torque and high-end power. When combined with the smoothness of a straight 6 layout, the power delivery of the 2JZ-GTE is silky smooth.
While the pistons on the 2JZ-GTE are not forged, the critical components surrounding the pistons are. To a degree, the 3.0L Toyota straight 6 has forged connecting rods and a forged crankshaft, which ensure safe modding. Because of these characteristics, the 2JZ-GTE is one of the most sought-after engine swap prospects ever. 2JZ-GTEs have been switched into practically anything under the sun, from Miatas to BMW M5. The adaptability, smooth power delivery, and insane power potential of the 2JZ-GTE win it an indisputable spot on this list.
The BMW B58 engine
Thus far, we’ve looked at two engines, both Japanese and from the 1990s. The engine we chose for this submission is neither of them. BMW has been producing inline 6-cylinder engines since 1933. Whereas many manufacturers have shifted away from inline engines in favor of V configurations, BMW has remained committed to inline engines and has proven rather adept at making them. In fact, they are so proficient at making straight 6 engines that they have won the overall International Engine of the Year Award with inline 6 engines eight times. It is quite an accomplishment. One of these engines was the BMW B58 straight six.
The BMW B58 engine, launched in 2016, is a 3.0L turbocharged inline 6 with direct injection. The B58 was created to replace the popular but aging N55 engine found in top-tier, regular-production BMW vehicles. The B58 engine has a few design elements with the BMW N55 engine, but it also differs in some significant ways. The 3.0L B58 engine is closed-deck, but the N55 engine is open-deck. The B58 is also charged with water-air, whereas the N55 is charged with air.
The strength of the inline 6 engines we’ve picked so far is a recurring trend. The BMW B58 engine is no different. The BMW B58, like the Toyota 2JZ-GTE, has forged connecting rods and a forged crankshaft. Furthermore, the B58, like the 2JZ, can manage far more power than it outputs in stock condition. Because of its twin-power turbo technology, the BMW B58 delivers power more smoothly than nearly any other engine available. In overall, the B58 has very few flaws and is quickly becoming a cult classic as a result.
BMW B58 Inline 6 Engine Specifications
The 3.0L BMW B58 shares several similarities with the Toyota 2JZ-GTE that we discussed earlier. Because of its similarities, many people refer to the B58 as the BMW 2J. Their incredible strength and insane power potential are their two most notable similarities. The B58’s strength stems mostly from its closed deck design, which includes forged connecting rods and a forged crankshaft. The B58’s forged crankshaft is the outstanding component, with 36% greater fatigue resistance, resulting in a longer service life with stock power.
The BMW B58 features a rather high compression ratio when compared to other high-performance turbocharged engines. In general, combining forced induction with a low compression ratio is a preferable idea, but modern technology allows the B58 to retain an 11.0:1 compression ratio without placing too much strain on the internal components. Increased compression is proven to increase baseline horsepower, thus the B58 has the best of both worlds.
With standard internals, the B58 can produce 600-650 horsepower and a similar level of torque. As a result, the B58 is widely used in the aftermarket. There are numerous aftermarket accessories for the BMW B58 that can significantly improve performance, such as new turbos, a better tune, an enhanced downpipe, and many others.
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4.0L Inline 6 AMC
The AMC 4.0L I6 engine is an outlier when compared to the other engines on this list. The Nissan RB25DET, Toyota 2JZ-GTE, and BMW B58 are all high-performance engines found in iconic sports vehicles. The AMC I6 is far from a high-performance engine. That being said, it exemplifies everything a great inline 6 should be. The AMC I6 is not just one of Jeep’s longest-running engines, having been launched in 1964, but it is also one of the most identifiable American engines ever produced.
While there are several engines in the AMC I6 lineup, the 242 AMC I6 is the standout. The AMC 4.0L inline 6 balances all of the attributes that make the inline 6 design so appealing. For example, the AMC 4.0L straight 6 is noted for its high torque, smooth power delivery, and long lifespan. The AMC 242 I6 was first used in the Jeep Cherokee XJ and Cherokee MJ, as well as the Wagoneer and Commanche, in 1987. The AMC 4.0L I6 engine helped all four of those cars become renowned as some of the best Jeeps ever produced.
Finally, Jeeps powered by the 4.0L AMC straight 6 have retained their worth very well throughout the years, thanks in large part to the 4.0L straight 6. Maintenance is usually very cheap because they are simple engines that are easy to work on. Components are also plentiful, as there are millions of AMC straight 6s on the road.
AMC 4.0L Straight 6 Engine Specifications
The AMC 242 I6 engine is the epitome of an American inline 6 engine. The 242 is a powerful, though heavy, engine with a cast iron block and head. While producing only 185 horsepower, the AMC I6 has a 7-bolt main engine, which ensures less stress over time. The inline 6 engine replaced the previous AMC carbureted 258 CID engines seen in older Jeeps. Because the 4.0L is fuel injected, it is the better option for offroading, as carbureted engines struggle when not on level terrain.
Throughout its lifespan, the AMC 4.0L had numerous major upgrades. The first 4.0L I6 engines used a revolutionary Renix engine management system, which was too complex for most shops to get codes from at the time. This technology was eventually replaced by a more standardized Chrysler multi-point fuel injection system, which simplified problem diagnostics. In 1996, the 4.0L received another update. With additional webbing and a stud girdle for the main bearings, this redesign reinforced the block even further. These latter reinforced engines were labeled “PowerTech.” Despite their bottom-end strengthening, early PowerTech engines were known to have cracked heads.
Barra Straight-6 Ford
This is an engine that most people outside of Australia have never heard of. The Ford Barra inline-6 engine was only available in Australian-spec Ford Falcons. Ford Australia had a long history of developing straight-6 engines prior to the debut of the 4.0L Ford Barra in 2002. The Barra evolved from Ford Australia’s previous “Intech” straight 6 engines produced between 1998 and 2002. In many ways, the Barra marked a farewell to their earlier experiments.
No one expected the Ford Barra engine to be very exciting or creative when it first appeared on the scene. In actuality, with a massive cast iron block and a rather simple design, it appeared fairly rudimentary. Nonetheless, this would turn out to be the Barra’s greatest asset. Moreover, the Ford 4.0L Barra is reported to be capable of producing close to 1,000 horsepower on stock internals. This certainly appealed to the tuning crowd, giving the Barra I6 a cult-like following. There are Barras out there with 2,000 horsepower or more thanks to internal modifications.
Because the Barra was only available in Australia, finding one in the United States can be challenging. Because the Ford Barra I6 was manufactured until 2016, there are still quite a number in decent condition. The Barra is still available as a crate engine from Ford and other aftermarket retailers. While it can endure comparable power figures to the Toyota 2JZ-GTE, the Barra does not receive the same aftermarket support due to its regional exclusivity.
Specifications for the Ford Barra Straight 6 Engine
While the base Ford Barra was originally marketed as a normally aspirated inline 6, turbo grade was also available in the Falcon XR6 Turbo. Both engines are DOHC, 24-valve engines with Ford’s VCT variable valve timing system. The Barra was available in both naturally aspirated and turbocharged versions, as well as petrol and liquid petroleum gas. There are 11 varieties of the inline 6 Barra in total, with even more if you include the V8 Barra variants.
The engine specs vary greatly due to the large range of versions in the Barra engine family. The compression ratio of naturally aspirated and turbocharged Barra engines, for example, ranges between 8.47:1 to 12.0:1. The turbocharged Ford Barra engine received stronger pistons, increased fuel pressure, and a big Garrett GT35/82r turbo. Power improved significantly over the years as Ford perfected the Barra formula. The N/A Ford Barra inline 6 initially produced 244 horsepower, with the most powerful variation producing 436 horsepower towards the end of the engine’s lifespan.
While the Barra is not the most well-known straight six engine on this list, it is one of the most capable. There’s no doubt that the Ford Barra belongs on a list of the best inline six engines ever built.
Conclusion: The Greatest Straight/Inline 6 Engines Ever Built
Inline engines are frequently left behind in favor of more current layouts when it comes to engines. V6 engines have left inline 6 engines in the dust, at least in terms of popularity. Straight 6 engines are simply too lengthy to be functional in today’s front-wheel-drive vehicles. Having said that, there are still manufacturers who respect the straight 6 layout and continue to construct them to this day.
The majority of the inline 6 engines on this list have been chosen for their durability, smooth power delivery, and power potential. If you ask us, those are some of the most desired characteristics that an engine might have. Toyota’s 2JZ-GTE, RB25DET, and BMW B58 are all shining examples. They all arguably outperform the inline 6 class, with some claiming them to be among the best engines ever created. While other engines may be stronger and more powerful, inline 6 engines will always be overlooked underdogs.