For many vehicle owners, the various numbers and terms used when referring to different vehicles and the engines in them can become overwhelming. To mechanics and enthusiasts, these terms tell you loads of important information on the mechanical makeup of a vehicle.
One of the most telling descriptors of a car is the engine configuration, which you have most likely heard or seen before. Configurations like the I4, V6, and V8 dominate the consumer automotive market, each with its unique characteristics and strengths.
We’ll cover what these terms mean, the benefits of each, and why some of these configurations are more common than others.
How to Read An Engine Configuration
The Letter
The system in which we refer to engine layouts is fairly simple, most often consisting of a single letter and a single number.
The letters are used to indicate how the pistons are laid out within the engine. For instance, the “V” that comes before V6, V8, etc. actually signifies that the pistons are arranged in two rows angeled away from each other creating a V-like shape.
On the other hand, “I” refers to an inline engine, where the pistons are instead arranged in a single straight line and facing directly upwards. These inline engines are also commonly referred to as “straight” engines, so you may hear “straight-six” rather than inline-six or I6 for example.
The exception to this naming convention would be “flat” engines, which are essentially V-shaped engines except the pistons lie flat horizontally rather than at the 60-degree angle of a V. These are less common, but still widely available in vehicles from brands like Subaru and Porsche. This layout is occasionally referred to as “H” engines.
Other piston layouts exist, such as “W” engines which resemble two V-shaped engines side-by-side (similar to the letters themselves). However, these unorthodox engine layouts are rarely used due to manufacturing and maintenance costs as well as their large size and low efficiency.
The Number
While the letter gives you information on the shape in which the pistons are laid out, the number instead tells you the number of pistons in the engine.
So in an I4 engine, one of the most common out there, there are a total of four cylinders sitting in an inline formation. Compare this to a V8 engine, where a total of eight cylinders are split into two rows (or banks) of four and angled away from each other; creating the V-shape that it derives its name from.
Most Common Engine Configurations
While manufacturers have experimented since the early 1900s with various unique engine configurations, there are a select few that have stuck around over the years for good reason.
Due to the size of engines and limited space in engine bays, some piston layout and cylinder count combinations are simply impractical for consumer vehicles.
For example, an extremely long engine configuration such as an inline-eight (I8) would be nearly impossible to fit in most vehicle engine bays. Instead, a V8 configuration has a more compact footprint with the same amount of cylinders.
Due to the unique size constraints and use-case of each vehicle, manufacturers must choose the engine configuration that best fits the specific needs of that model. For this reason, the vast majority of modern cars come equipped with one of the following engine layouts.
Inline-four
The inline-four (I4, straight-four, four-banger) engine is the most common configuration among modern consumer vehicles. As of 2021, over 59% of new light-duty vehicles sold are equipped with a four-cylinder configuration. The compact design and low number of engine components make it one of the most practical for commuter cars and compacts.
Inline-fours are well known for their reliability, as the inline configuration only requires a single cylinder head; reducing complexity and repair costs.
Their small size also contributes to the other major benefit of an I4, fuel economy. The smaller displacement of a four-cylinder, which typically falls between 1.3-2.5 liters in modern cars, allows the engine to use a relatively low amount of fuel compared to larger-displacement motors.
Four-cylinders are perfect for most general applications but fall short in more specialized and performance-focused vehicles. While the small displacement means less fuel usage, it usually means less power and torque. Vehicles that require power outputs or towing capability will often opt for a beefier engine, such as a V6 or V8.
Four-cylinders also suffer from pulsations in power delivery, as having only four cylinders means the next combustion stroke cannot begin until the previous cylinder has completed its combustion cycle. These pulsations cause noticeable vibrations through the chassis. This is a non-issue in an engine with five or more cylinders since there will always be another cylinder’s combustion overlapping as one cylinder completes its power stroke.
Even with these drawbacks, the I4 configuration has cemented its spot as the perfect choice for the majority of cars on the road. Modern developments in engines have also mitigated some of the power concerns, as the advent of turbocharging in commuter vehicles allows for both increased horsepower and efficiency.
As larger engines continue to be phased out due to environmental concerns, expect the four-cylinder to stick around and find its way into more performance vehicles as manufacturers squeeze even more power from these small motors.
Inline-six
The inline-six (straight-six, I6) has long been a preferred choice of manufacturers looking for a powerful and balanced engine. Straight-sixes have lost some of their market share over time with the improvements of V6 and I4 designs, however, the simple single-head design and superior balancing have allowed it to stay a common choice in some commuter vehicles as well as performance and luxury options.
The largest benefit of a straight-six is its perfect engine balance. Other engine configurations like the I4 and V6 lack this feature and have significant imbalances, leading to vibrations through the chassis.
The straight-six’s smooth feel and balance is a result of its configuration and firing order, as with six cylinders the front and rear trios of pistons will move in pairs. Since each side is experiencing a cylinder combusting, the rocking effects of both are canceled out.
Compare this to a less common configuration like an inline-three, which is not able to cancel out its rocking motion due to the uneven firing order. This issue holds in V6 motors as well, since they essentially act as two inline-threes connected.
While they have become a less common choice over the last few decades, some brands still value the refined feel and sound of an I6. BMW, Mercedes-Benz, Stellantis (GM, Alfa Romeo), and Jaguar/Land Rover all have new vehicles equipped with inline-six engines.
V6
The other common configuration for six-cylinder engines is the V6, which consists of two banks of three cylinders. V6 engines bring a few improvements over their inline counterparts, such as the double bank design that shortens the length and allows it to fit in vehicles that otherwise could not fit an I6.
While their lower size footprint is a large benefit over the inline layout, the double-banked design also comes with a major tradeoff; balance. As stated earlier, the V6 configuration is essentially two I3 engines conjoined, meaning they suffer from the same balance issue as the three-cylinder due to an odd number of cylinders in each bank.
This imbalance issue stunted the adoption of V6 engines in the early days, but with the development of harmonic balancers and changes to the firing order, the balance of V6 motors has drastically improved and made them a practical choice in many types of vehicles.
Due to their size and fuel consumption, six-cylinders (both inline and V) have begun to lose market share to the improved four-cylinder options of modern cars. However, these engines still fill an important role in the automotive market and remain commonly used by various brands with the addition of forced induction.
V8
The V8 has long been one of the most recognizable types of engines, largely due to its constant presence in the American muscle scene. Since the introduction of the original “pony car”, the 1964½ series Ford Mustang, the V8 has been a defining feature of American performance vehicles.
That isn’t to say the V8 isn’t used elsewhere, as European brands like Audi, BMW, Mercedes, and Porsche have all produced or still actively offer V8 options in their vehicles.
V8 motors are renowned for their power, as the larger displacement of the extra cylinders allows for increased combustion and increased horsepower and torque outputs. This makes the V8 a prime choice for larger luxury or performance vehicles that need a little more punch to their motors.
Despite it being one of the V8’s primary benefits, the larger displacement and extra cylinders are also the cause of one of its largest shortfalls. V8 motors are notoriously bad on fuel, as they sacrifice efficiency for power. Improvements have been made over time, aided by the use of efficient forced induction and hybrid systems, however, the industry trends point towards the V8 falling out of favor with manufacturers due to increased environmental regulations.
Even American vehicles whose identity was largely related to their V8 power and grunty sound have begun to transition to more fuel-friendly options. Dodge, known for their large and powerful V8s, has announced the end of their V8 muscle car production and will instead use straight-sixes and electrified powertrains for future performance vehicles.
Flat Engines (Flat-four, Boxer-four, Flat-six)
A less common, yet still very notable engine configuration is the flat design. Flat engines are essentially V engines that sit horizontally rather than at an angle.
The most common type of flat engine is the four-cylinder boxer, which derives its name from the two pairs of pistons mounted at 180 degrees that create an outward “punching” motion. Subaru is famous for its boxer-four, which has found its way into nearly every Subaru platform at some point. The WRX, WRX STi, Legacy, Forester, Outback, and BRZ have all shipped with a boxer option at one point or another. Subaru isn’t alone in the boxer world though, as Porsche’s 718 platform comes standard with a flat-four rather than their traditional flat-six.
The flat-six is a mainstay in Porsche’s lineup, coming as the only engine choice for their flagship 911 since its introduction in 1964. As of this article being written, the Porsche flat-six is the only engine of its kind available in a new vehicle.
Flat engines provide some considerable improvements over V-shaped engines, as the 180-degree angle mitigates the balance issue of other options that use two banks of cylinders. Flat engines also sit slightly lower and contribute a lower center of gravity, improving the handling of the vehicle.
Having two cylinder heads means that flat engines experience the same increase in production and maintenance costs as a regular V-shaped engine. The lack of angeled pistons also means that these cylinder banks take up more width, and may not fit well in some smaller engine bays.
Engine Diagnostics & Repair in Riverton
No matter what type of engine you have, trust the experienced technicians at Matson Point S in Riverton, Utah for any engine diagnostics or repairs! Our team has extensive training and the proper equipment to service any make and model. Give us a call today to speak with our friendly service advisors or schedule online!