Have you ever been curious as to why certain manufacturers favour certain engine architectures over others. Subaru is well-known for using ‘horizontally opposed’ engines. Many Porsche engines utilised the ‘inline’ six-cylinder architecture. Other manufacturers opt to go for the V6 configuration. And so, it goes.

One could also ask why some manufacturers build 4.0-lite V6’s while others build 4-litre V8’s. The Nissan Pathfinder and Toyota Fortuner both employed 4.0 V6 engines. Land Rover, on the other hand, used a 4.0 V8 in the Discovery.

Which is better? In terms of power, the answer is not so straight-forward. When considering the various engines, the layout is not the biggest contributing factor to how much power is produced.

I would go so far as to propose that, with a small dose of ingenuity (and a bigger dose of cash), a four-cylinder engine can produce the same power as a V12.

Comparing the Mercedes Benz M139 engine and the V12 Aston Martin Vanquish engine, one can see that kilowatt values are within 10% of each other. Not at all shabby considering the Mercedes engine has third of the cylinders and a third of the capacity. 

So, if it is not power what makes manufacturers choose different engine layouts?

Here are the advantages and disadvantages of each layout.

1. Inline 4- Cylinder (I-4)

Let’s start with one of the most commonly used engines, the inline four cylinder. There’s a reason it’s common, largely because it’s so simple: one-cylinder bank, one-cylinder head and one valve train. Here’s all you need to know:

Advantages:

-The four-cylinder, inline four is small and compact, meaning it easily fits in nearly any engine bay.

-It’s also lightweight, and with only one exhaust manifold, weight is further reduced.

-With only one-cylinder head, there are fewer moving parts than engines with multiple cylinder banks. This means less energy is lost which reduces the probability of malfunctions.

-Primary forces are balanced because the outside two pistons move in the opposite direction of the inside two pistons (see picture above).

-Four-cylinder engines are easy to work on; the cylinder head is the highest point which makes spark plug jobs and valve train access very easy.

-Four-cylinder engines require lower manufacturing costs.

Disadvantages:

-Secondary forces are not balanced, which ultimately limits the size of the engine.

-Inline fours will rarely exceed 2.5 litres to 3.0 litres.

-Larger four-cylinder engines will often require balancing shafts to cancel the vibration caused by the secondary imbalance.

-High centre of gravity compared to some layouts (H4). -Not as rigid as some layouts (V6, V8).

2. Horizontally opposed (H4 or H6)

From a performance standpoint, there aren’t many options as attractive as an engine with horizontally opposed cylinders. The boxer four isn’t nearly as common as the other engines on this list, but from an engineering standpoint it’s a logical choice for your race car. Subaru produce both 4-cylinder (H-4) and 6-cylinder (H-6) versions of this engine.

Advantages:

-Primary and secondary forces are well balanced. This is a smooth engine.

-This allows for less weight on the crankshaft, resulting in less power lost to rotational inertia.

-Low centre of gravity allows for better handling.

Disadvantages:

-Packaging size: these are very wide engines.

-Flat engines were once used in Formula 1 for their performance advantages, but due to their width they obstructed airflow and are no longer used.

-Complexity - two-cylinder heads/valve trains.

-Rocking couple (plane imbalances) due to offset pistons to allow for the connecting rods to connect with the crankshaft.

-Maintenance can be challenging if packaging is tight.

3. Straight-six (I-6)

An engineer’s object of affection, the straight-six is the result of tacking on two more cylinders to an inline four engine. BMW loves them. Porsche loves them.  And it’s the layout of one of the most well-known boost-ready engines, the Toyota 2JZ. So, what’s so special about the straight-six?

Advantages:

-The straight-six is Inherently balanced.

-The layout combined with its firing order leads to essentially the smoothest engine out there.

-V12s and Flat-12s are the next step in further reducing vibration, as they are two I6s matched together.

-Lower manufacturing cost - single cylinder block with all the cylinders in one orientation.

-Simple design, easy to work on much like the I4.

Disadvantages:

-Packaging can be difficult due to the length.

-Not ideal for FWD vehicles. -High center of gravity (vs flat engines).

-Lower rigidity than V engines as it’s long and narrow.

4. V6

If we were to cut a straight-six in half and match the two-cylinder banks to a common crank, we would result in a V6. The V6 is a common layout when there are six spark plugs involved. Sometimes the angle differs. The V6 shown above is a narrow 60 degree angle. Other manufacturers use a 90 degree angle. Why use it?

Advantages:

-They’re compact and can easily be used for both FWD and RWD vehicles.

-Allows for greater displacement than four-cylinder engines, typically meaning more power.

-Rigid design.

Disadvantages:

-Two-cylinder heads means added cost, complexity, and weight.

-Additional rotational inertia and friction (more moving parts).

-High centre of gravity vs flat engines.

-Cost is often greater than inline.

-Secondary imbalance requires additional weight on the crankshaft.

-Two exhaust manifolds mean additional weight.

5. V8

When you add a cylinder to each bank of the V6, you get an icon in both American muscle and European exotics - the V8. It can produce a refined whine, or a shuddering burble. So, what makes this layout such a popular choice?

Advantages:

-Packaging size (short in length).

-Good balance, depending on the crankshaft type and firing order (flat plane vs cross plane).

-Rigid design.

-Allows for high displacement.

Disadvantages:

-Like a V6, the V8 engine’s weight can be high.

-Additional rotational inertia and friction (more moving parts).

-Cost and complexity will be higher.

-Higher centre of gravity vs flat engines.

-Engine weight is usually increased.

-Packaging is large, typically restricted to RWD/AWD vehicles.