Your Complete Guide To The Inline Engine

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Everything you need to know about inline engine configurations

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The internal combustion engine has been around for well over 150 years, and in that time has been honed into an incredible piece of technology. While the majority still don't understand how car engines work, others have a strong preference for certain types of car engines. From V8s all the way to flat-fours, there are many ways in which one can arrange a set of pistons. In this article, we'll be discussing the famed inline engine or straight engine as some call it, including the pros and cons of an inline engine, different engine cylinder configurations, and some of the more frequently asked questions relating to the inline family. So strap in, and get ready for a smooth journey.

What is an Inline Engine?

The inline engine has been with us in one form or another since the early 20th century, and one of the first examples of an inline-six was produced by Spyker in 1903. Most cars on the road today use an inline-type engine, and this engine configuration continues to outsell all others, including the V6 and V8.

The term "inline" refers to the configuration of the cylinders in the engine block. In an inline engine, the cylinders are positioned in a straight line and can be configured as an inline 2, 3, 4, 5, 6, or 8 cylinder engine. Manufacturers prefer to call four-cylinder variants "inline-four engines," while engines featuring six or eight cylinders get called "straight" engines. Inline engines are used in several applications, including aeronautics, and are cheaper to produce than the more complicated, but ever-popular, V-engines, or the compact horizontally opposed engines.

The inline engine is not only cheap to construct, but requires no balancing components, which reduces cost and complexity, and offers smooth power delivery and good torque due to a longer cylinder stroke.

Inline Engine Configurations freepik.com

Inline Engine Advantages and Disadvantages

Every engine configuration has its upsides and downsides. Reliability, capacity, weight, and more can all play a role in an engine's overall performance. Here is a breakdown of the advantages and disadvantages of the inline engine:

Best Tuned Jaguars Ever Made
Best Tuned Jaguars Ever Made
Honda Ridgeline Vs. Hyundai Santa Cruz: Baby Truck Battle
Honda Ridgeline Vs. Hyundai Santa Cruz: Baby Truck Battle

Pros and Cons

  • It's cheap to produce - Due to its simplistic design, manufacturers can keep the production cost of inline engines to a minimum. That would explain why the majority of engines found in cars today are inline units.
  • Lots of torque - Due to the pistons' longer stroke, inline engines tend to produce good torque and have to rely less on high compression ratios and turbochargers to make decent power.
  • Less complex/more reliable - Due to the simplicity of inline engines, they tend to be easier to work on and have proven to be very reliable when taken care of properly. This is another reason why inline engines tend to save money in the long run.
  • Smooth six - Inline-6 motors are naturally balanced and offer a trademark smoothness that few other engine types can match.
  • They tend to be big - Inline motors are usually larger than their horizontally-opposed V-series and rotary counterparts, due to the cylinders' layout. On cars with larger inline motors such as a straight-six engine mounted longitudinally, passenger legroom might be shortened due to the engine's sheer size.
  • Inline-four engines can become unbalanced - Inline four engines are limited in size due to balancing issues; that's why you won't regularly see inline engines exceeding 3.0 liters. Larger four-pot engines can require balancing shafts.
  • Rigidity and center of gravity - Inline engines tend to sit higher in the vehicle, which can affect the center of gravity, and in turn, the car's handling. Due to its layout, it is also not as structurally rigid as something like the V6 engine.

Famous Inline Engine Examples

A few of the most legendary examples of the inline motor to date include:

  • Nissan RB - Nissan's range of RB engines has been used across a wide variety of applications, but is most famous for its use in the Nissan Skyline GT-R engine bay, where the motors were dubbed the RB26DETT. This engine features a cast-iron block with an aluminum head and six individual throttle bodies. Power was rated at around 316 horsepower at 6,800 rpm and 289 lb-ft of torque at 4,400 pm, although independent testing has shown that these engines can produce up to 400 hp from the factory n the R34 Skyline GT-R.
  • Toyota 2JZ-GTE - The Toyota 2JZ engine is legendary amongst tuners and gearheads alike for its massive power capabilities, and one regularly sees these engines make over 1,000 hp, reliably. On the internet, anyway. The stock engine found in the turbocharged A80 Supra develops 320 horsepower and 315 lb-ft of torque, but the engine's cast-iron block can handle much more, and it's not uncommon to see cars with stock blocks push out well over 700 hp.
  • AMG M139 - This is the newest engine on our list and one of the most impressive. Currently doing battle in the hyper hatch segment abroad in the A 45 S, Mercedes-AMG's M139 inline-four cylinder engine packs a massive 416 hp at 6,750 rpm and 369 lb-ft between 5,000 rpm and 5,250 rpm. These power outputs make it the most potent roadgoing 2.0-liter engine in the world.
  • Honda F20C - Honda's F20C engine shot to stardom when it featured in the S2000, an RWD two-door sports car, and can rev up to 9,000 rpm. This naturally aspirated engine (the only of its kind on our list, although many Honda motors are brilliant) offered 123.5 hp per liter, which is still one of the highest figures to date, and made up to 246 hp in total in JDM spec. Its N/A specific output was only bested by the 4.5-liter V8 in the Ferrari 458 Italia in 2010, years after the Honda sportscar had gone out of production.

Notable mentions:

Audi DNWA TFSI 2.5-liter turbo (TT RS, RS 3)

BMW N54 3.0-liter twin-turbo straight-six (135i, 1 Series M Coupe)

BMW M50/S50 series 2.5-3.2-liter straight-six N/A (E36 328i, M3)

RB26 unsplash.com
Honda Engine unsplash.com

FAQs

What is the best inline layout?

The inline 4-cylinder engine is the most popular in the motoring world and is the best from a cost and reliability point of view, but if you're more performance-minded, then the answer is without a doubt the straight-six motor. Not only does it offer lots of torque and smooth operation, but in certain guises, it can make lots of power. The Toyota Corolla, both sedan and hatchback variants, feature an inline-four configuration, as does the Kia Sorento. While the BMW 4-series has an inline-4 in standard configurations, too, the M440i variant upgrades to a six-cylinder for more power.

Are five-cylinder inline engines any good?

The short answer is yes. The most well-known modern inline 5-cylinder engine has to be the 2.5-liter TFSI engine used in the Audi TT RS. This 394 hp engine offers brutal torque and a soundtrack unlike any other gas-powered engine on the road. Other famous cars with five-cylinder engines include the Audi Quattro, Volvo 850R, and Ford Focus ST225.

Are inline engines suitable for modifying?

Inline four (I4) and straight-six engines have been the darlings of the tuning world for decades and continue to be the go-to engine configurations for leading tuners. Examples of modern inline tuner engines include the Toyota 2JZ engine and the BMW B58B30, which coincidentally is also used in the fifth-generation Toyota Supra. However, even Volkswagen's TFSI range of 2.0-liter turbo-fours is a great platform for tuning.

Which cars have three-cylinder engines?

Although the inline-3 engine is not a popular engine configuration in the USA, there are still several vehicles on sale that make use of three-cylinder motors. Examples include:

  • Mini Cooper Convertible, Hardtop, and Countryman
  • Mitsubishi Mirage
  • Buick Encore GX
  • Ford Escape
  • Ford Bronco Sport
  • BMW i8
  • The Koenigsegg Gemera will have an unusually large inline-3, too
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