The immediate differences between a straight-six and a V6 engine are easy to spot: One is composed of six cylinders in a straight line, while the other has two arrays of cylinders aligned in a V formation. That’s easy enough to wrap your head around, but what’s the reason for such a difference?
What Is a V6 Engine?
Here’s how a V6 validates its more complicated shape. Since there are two half-length rows of cylinders, the V6 engine is naturally half the length of a straight-six. This is the premier benefit of this style of engine. In order to maximize the space both under the hood and in the rest of the vehicle, the more compact engine style is an excellent tool for car designers. Since the V6 does have six cylinders, it is a good option for making powerful yet small cars. In terms of power, the shape of a V6 engine opens up a convenient space for turbos as well.
There are several different angles of V engine that can exist. For example, the Ford EcoBoost V6 engine has 60 degrees of separation between the two banks of cylinders. There are other V6 engines that can be 90 degrees apart, and 120 degrees, as well. Of course, there are other angle options for this engine, but those are the most common.
What Is a Straight-Six Engine?
Straight-six, or, as they are also called, inline-six engines, are composed of six cylinders linearly aligned. This alignment is the de facto way of making an engine, as it is rather simple. For that reason, straight-six engines are more straightforward to repair and manage than their V6 counterparts. Since the cylinders are more spread out, each can be clearly seen and managed. Additionally, since straight-six engines are composed of an even amount of cylinders, they can be fired off in a way where the vibrations of one piston counteract the other, making them run smoothly.
Some automotive audiophiles claim that the sound of the straight-six sounds much nicer than the V6, but this claim is as controversial as it is subjective. There are some sound differences between the two engines, but they are hard to parse, as the exhaust, muffler, and the specific make of the engine all impact the exhaust note as well.
Pros and Cons of Straight-Six and V6 Engines
There are, of course, problems with both types of engine. As previously mentioned, the V6 is comparatively harder to work on given its compact design. While that doesn’t mean that it’s impossible to repair on your own, it may be easier to find your way around the engine block if it was an inline-six. Also, V6 engines are made additionally complicated because of their issues with vibration. Unlike the straight-six engine, which has a single row with an even number of cylinders, the V6 is essentially made of two 3-cylinder rows. Because of it being an odd number, it cannot compensate for the excess vibrations. This is remediated by placing weights on the end of a balancing shaft.
The issues with an inline-six are mostly about space. Inline-six engines are long, and developing a car that can fit it along with all of the other car parts can be a difficult process. For this reason, these engines end up costing car designers quite a lot more money in research and development. A V6, on the other hand, can be plopped down into most cars with little fuss. Even though V6 engines are more expensive and complicated to produce than straight-six engines, the process of designing a car to accommodate such a bulky engine, along with all of the modern safety tech and assorted creature comforts that are standard on any new vehicle, is an arduous process. For this reason, inline-six engines aren’t the default choice for 6-cylinder engines currently.
The Future of the Straight-Six
The preference away from the straight-six may change, however. Mercedes has developed a new inline-six engine that, if successful, could reintroduce the straight-six engine into today's mainstream vehicles. To avoid having to run a series of timing belts around the engine and having every necessary component of the engine being attached directly to it, a powerful alternator will instead be installed, allowing for more creative allocation of space around the engine. The many advances made with electric automobiles have paved the way for more easily designed gas-based vehicles as well, as this innovation may very well save the inline six-engine design from its otherwise seemingly inevitable extinction.