5 Inline

While inline-six engines are among the most reliable and powerful engines ever produced, some turned out to be real duds.

Over the years, the inline-six or straight-six engine configuration has proved to be one of the most successful engine designs. Its low-end torque and smooth power delivery made it the go-to design during the 20th century. Inline-six engines powered iconic '60s classic cars like the Jaguar E-Type and Toyota 2000GT and several legendary '90s Japanese sports cars like the Supra MK4 and the Skyline GT-Rs.

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However, not every automaker got it right with inline-six engines, as some were downright unreliable while others delivered mediocre performance. Today, the inline-six engine is a dying breed, with only a few top automakers like BMW and Mercedes-Benz still stuck with inline-six engines.

Due to their reliability and tuning potential, inline-six engines are some of the most popular engine swaps for tuners and speed freaks. Still, there are a few others that are absolute junk. Here are the five best inline-six engines we want under our hood and five others we'd rather avoid.

Although TVR doesn't have many engines under its name, the Speed Six ranks among the best inline-six engines ever produced. Built from 1999-2007, the TVR Speed Six powered several TVR cars, including the Tamora, Typhon, Sagaris, T350, and Cerbera.

Producing between 350-406 hp, the TVR Speed Six punched way above its weight for a naturally aspirated engine. A monster performer, only a few engines can beat the TVR Speed Six when it comes to speed and performance, not forgetting its brutal exhaust note. The engine propelled the Tuscan Speed Six from 0-60 mph in just 3.68 seconds.

Although a highly tunable engine, the N54 is one of the worst BMW engines when it comes to inline-six engine reliability. Introduced in 2007 in the E90/E92 335i, the N54 soon made its way into a handful of other BMW cars before the Bavarian automaker discontinued it in 2016.

Today, the N54 gets slandered for being a money pit. A deeply flawed engine, the N54 will bankrupt you with all sorts of repairs, from oil leaks and cooling system failure to turbocharger problems and other miscellaneous repairs, but the most notorious problem is the failing High Pressure Fuel Pump (HPFP). Owners reported that HPFP problems occurred as early as 60,000 miles, a prevalent issue that forced BMW to recall over half a million units following a class action suit filed in 2009.

The 325T is the final and the most powerful variant of the iconic Ford Barra engine. Boasting incredible power out of the box (436 hp and 425 lb-ft of torque), the Barra 325T's internals can also withstand huge amounts of strain. On top of that, the engine has a very stout block, known to go over 250,000 miles without major repairs. Its reliability is up there with the likes of the RB26DETT and the 2JZ-GTE.

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Following its discontinuation in 2016, the Barra 325T gained incredible popularity among tuners who could coax over 800 hp from the inline-six motor while on stock block, pistons, and rods. Today, the Barra 325T is a common engine swap in Falcons, Mustangs, and even Shelby GTs.

The Triumph six-cylinder engine was basically an evolution of the Standard Motor Company's inline-four Standard Eight, albeit featuring two additional cylinders and bigger displacement. It powered a wide range of Triumph cars, including the TR250, TR5, and the iconic TR6.

Despite the Triumph TR6's popularity, the engine was somewhat disappointing as it suffered from reliability and mechanical issues like overheating and fuel vaporization that stalled the car. While the TR6 was an important car in the British automaker's history, we reckon the unreliable engine was not, and it's an inline-six engine we'd rather forget ever existed.

BMW has produced many iconic engines, from four-, eight-, ten- to twelve-cylinder engines, but its history remains intertwined with the inline-six motor. That said, few BMW inline-six engines resonate with tuners and enthusiasts as vibrantly as the S54. Introduced in 2000 in the third-generation E46 M3, the S54 quickly became the most beloved BMW engine.

Thanks to the cast iron block build, the S54 was very reliable. But the S54's real party piece was its smooth power delivery and the goosebump-inducing exhaust note. Producing over 300 hp in stock form, it's no surprise the S54 won the Best New Engine and the International Engine of the Year awards in 2001. On top of that, it was the world's best engine each year until 2006 in the 3.0 to 4.0 liters category.

The N57D is a turbocharged diesel block that powered several BMWs between 2011 and 2015. Replacing the B57 engine, the N57D had a short production life, as it was one of the worst inline-six engines to avoid for reliability issues. BMW ultimately replaced it with the B57 after just five years.

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The N57D was prone to engine fires, a problem that forced U.K. police forces to either retire, withdraw or limit the speed of all cars powered by the N57 engine. As if that weren't enough, the N57D suffered from a myriad of other problems, including crankshaft pulley failure, swirl flap failure, and glow plug relay failure, among others.

In production from 1991 through to 2002, the 2JZ-GTE needs no introduction. It is arguably the best inline-six engine ever produced. If anything, the MK4 Supra owes its legendary status to this iconic Toyota engine. Boasting bulletproof reliability, the 2JZ-GTE has a cult-like following among JDM enthusiasts and tuners.

Producing 320 hp and 315 lb-ft of torque from the factory, power junkies soon realized 500 hp from the 2JZ-GTE wasn't an overstretch. Today, the 2JZ-GTE is among the best tuner engines, capable of producing over 1,000 hp with added boost and other performance mods.

Powering the MK3 Supra, the 7M-GTE doesn't attract the same reputation as the JZ-series engines that succeeded it, and for a good reason. While the 232 hp and 240 lb-ft of torque was decent for its time, it was downright unreliable due to a factory defect.

Shortly before its launch, a strict ban on asbestos products forced Toyota to use other materials in making the 7M-GTE's head gasket. The result was a failing head gasket in many engines that resulted in oil and coolant leaks, as well as bearing issues.

The Nissan RB26DETT is another iconic Japanese engine and one of the best inline-six engines for speed and performance. It powered three generations of the legendary Skyline GT-R from the R32 to the R34, boasting unmatched performance that deservedly earned the R32 GT-R the 'Godzilla' nickname.

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Although Nissan advertised the RB26DETT to produce 276 hp and 260 lb-ft of torque in adherence to the Japanese Gentleman's Agreement, real world outputs were over 300 hp. Like the 2JZ-GTE, 1,000+ hp from the RB26DETT is no big deal. One of the most reliable inline-six engines, we would easily swap the RB26DETT into our cars without hesitation.

Introduced in 1959, the Nissan P40 is a 4.0-liter gasoline-powered inline six-cylinder that powered the Patrol up to the early 2000s. Although a reliable engine, we would steer clear of the P40 due to its lackluster power and performance.

The P40 put down a miserable 123 hp at its introduction, and subsequent updates over the years saw the engine gain just 20 hp in 1965. It's, therefore, no surprise that many Nissan Patrol owners swapped the P40 for something more powerful.

Sources: Hagerty, Performance Drive, Tuning Pro, and Ultimate Specs

Dennis Kariuki is a tech enthusiast who writes for Hotcars.com. Previously, he wrote for the.car .He likes covering the marriage between technology and cars. Besides that, he is big f1 fan. After working tirelessly through the week, you can be sure that on Sundays he is most likely enjoying and following motorsports events.