In-line 6: elegant and timeless
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In-line 6: elegant and timeless
There are certain mechanical architectures in the automotive world that stand out for their perfect balance, unique sound and polished performance, and the in-line 6-cylinder (L6) engine, whether in diesel or petrol form, is near the top of the list!
Renowned for its harmonious design and dynamic qualities, this engine continues to appeal to driving enthusiasts and engineers alike, even in this age of electrification and downsizing.
The six cylinders, as the name suggests, are arranged in a straight line along the crankshaft, the major advantage of this configuration being the natural balance that it creates. The symmetrical arrangement of the pistons and the firing order (1-5-3-6-2-4) means that the L6 cancels out almost all vibration, unlike a V6 engine, which is out of balance (1-4-3-6-2-5). As a result, the engine runs remarkably smoothly, making it a popular choice for luxury saloons, sports coupes and premium SUVs.
Then, of course, there is the enhanced durability that this balance promotes. With fewer internal components than a V-engine (just the 1 cylinder head instead of 2, 1 or 2 camshafts rather than 2 or 4, and 1 timing chain instead of 3, etc.) but still running smoothly, this engine can offer exceptional longevity when properly maintained.
The sound of the L6 is something else that appeals to enthusiasts. Less raucous than the V6 and more musical than a 4-cylinder engine, the melody of an L6 is a real acoustic signature. From the subtle purr at low revs to the exhilarating howl at the other end of the scale, this engine has won over generations of motorists, from BMW enthusiasts to Jaguar, Mercedes, Toyota Supra and Nissan Skyline owners.
A versatile engine
This engine first emerged in the early-20th century and quickly established itself in a variety of fields. As well as being fitted to a wide range of land vehicles, it also made a name for itself in aviation, particularly during World War I, thanks to Mercedes and BMW. By the mid-20th century, the L6 was powering both American and European cars thanks to its robustness and versatility, since it offered the perfect combination of power and torque at very low revs without the need for a turbocharger, unlike V6 engines, which had to climb up the revs to achieve the same amount of torque.
Iconic models such as the Nissan Skyline GT-R (RB26) and the Toyota Supra Mk4 (2JZ) have marked the history of sports cars with their legendary L6 blocks, renowned for their ability to cope with very high levels of power. While manufacturers such as Alfa Romeo, Mercedes, Opel and Volvo have all fitted their models with an L6, BMW has gone as far as making it a tradition. The Bavarian brand has been using it since the 1930s and it continues to be a key component of its models, notably in the 3 and 5 Series, the X5 and X6 SUVs and the M-series sports cars, with both petrol and diesel engines.
Challenges in the face of modernity
The popularity of the in-line 6-cylinder engine declined in the late-20th century due to its size, weight and weight distribution, with manufacturers preferring the more compact and economical V6s, which were also better suited to modern platforms. Nevertheless, the L6 has stood the test of time. Advances in engineering have made it possible to reduce its weight and incorporate technologies such as turbocharging, variable valve lift, camshaft shifting and hybridisation. Mazda, for example, has swapped its 4-cylinder diesel for a 6-cylinder turbo diesel with lightweight 3.3L hybridisation on its top-of-the-range models, consuming just 5.4L/100km (WLTP) and emitting 140g CO2/km – a significant difference compared with their 2.2L 4-cylinder diesel engine, which consumes 6.6L/100km and emits 173g of CO2/km.
Electrification could gradually make the in-line 6-cylinder engine a thing of the past over the coming years, although some manufacturers do still believe in its potential and continue to develop modern, less polluting L6s. Furthermore, the potential that e-fuels represent could help the L6 to maintain its prestigious place in the automotive industry.
By Loïc Schiocchet for Autotouring