I-4, I-6, V-6, & V-8 Engines - The Differences Explained

by Jeff Youngs

Automobile manufacturers offer a wide variety of engine types to meet customer demand, preferences, and utilization. Some of the most complex and powerful types are 10 and 12 cylinder engines found in ultra-luxury sedans and supercars. More commonplace, a wide range of popular auto manufacturers utilize the economical and rather simplistic I-4 and I-6 engines as well as the better balanced and powerful six and eight cylinder V configuration engines.

While a 10 or 12 cylinder engine will certainly leave any automobile enthusiast’s heart pounding, for the purposes of this article we are going to take a look at the most popular engine configurations in order to better understand each one and what some of the main differences are. The four most popular automobile engine configurations in today’s marketplace are the I-4, I-6, V-6, & V-8 with the I-4 being the most common.

I-4 Engine

An inline-four cylinder (also known as an I-4 or straight-four) engine is a very popular choice for today’s economy vehicles as the simple design allows for both efficiency and perfect primary balance. In an I-4 engine, all 4 cylinders are mounted in a straight line along a single crankshaft and oriented in an inclined or vertical plane.

Today, nearly all four cylinder engines use the inline-four layout, however, both Porsche and Subaru are exceptions. These manufacturers use a flat-four or horizontally opposed layout where the pistons lay in two sets of opposing groups along the crankshaft. In a four cylinder engine, this configuration can be referred to as H-4. This orientation allows for a lower center of gravity in a more compact design. The lower center of gravity provides better handling for a sport-like driving experience.

While the efficiency and simplicity of the inline four engine is an understandably popular choice for small engines, the design results in a secondary imbalance that becomes more pronounced as engine power and size increases. This causes a natural limitation on what type of vehicle and inline-four engine can be used in and the type of driving experience one can expect. As a result, larger automobiles and/or those that require more powerful engines normally use additional cylinders.

I-6 Engine

The straight-six or inline-six engine is like an inline-four in the fact that the cylinders are mounted in a straight row and together drive the crankshaft, however, instead of four cylinders, the inline-six utilizes six cylinders. While not as economically efficient as an inline-four engine, the inline-six is a larger engine that can provide more power and has both primary and secondary mechanical engine balance which results in much less vibration.

Dating back to 1903, the inline-six engine offers a simple mechanical design, but at the cost of a physically longer engine. By comparison a V-6 takes up roughly half the length as a similar inline-six. This was not an issue decades ago when cars were, on average, much larger but as automobiles have become more compact and engine compartment real estate becomes more scarce, the inline-six engine faces a distinct disadvantage. This has led most manufacturers to utilize a V-6 engine where they feel a six cylinder engine is appropriate or preferred.

As with an inline-four, a few manufacturers use a flat-six or horizontally opposed configuration (H-6).

V-6 Engine

A V-6 engine has six cylinders (two sets of three cylinders) arranged in a V pattern and mounted to drive a single crankshaft. The cylinder sets are normally mounted at a 60 or 90 degree angle to one another. The 60 degree angle allows a V-6 engine to fit comfortably into the same space as an inline-four. This configuration provides improved power and less vibration at no additional size when compared to its I-4 counterpart. The 90 degree angle V-6 occupies about the same space as a V-8. While not as powerful, this configuration provides a more economical option in both price and fuel efficiency for those interested in a luxury vehicle that is built around a V-8 but more attractively priced with a V-6 engine option.

When compared to an inline engine, the V-6 engine is both shorter and narrower. It also has a superior center of gravity and far less vibration. These benefits make it an excellent choice for modern front-wheel drive automobiles and those seeking a more comfortable and smoother ride.

V-8 Engine

As the name suggests, a V-8 engine is comprised of eight cylinders arranged in a V configuration that has two opposing sets of four cylinders. The most common mounting angles are 90, 45, 60, and 72 degrees. Imagine two parallel inline-four engines mounted along a single crankshaft and you have the V-8 engine in its simplest form.

Just like an inline-four, the V-8 configuration results in significant secondary imbalance leading to excess vibration. This imbalance and vibration causes a less comfortable driving experience and can lead to engine complications. Most manufactures solve this drawback by utilizing a crossplane crankshaft with counterweights. This solution eliminates vibration and leads to a much smoother feel. It is superior in comfort to both a V-8 with a single plane crankshaft and a standard V-6 engine.

While it reduces secondary imbalance and excess vibration, the crossplane crankshaft also reduces acceleration rates when compared to the single plane crankshaft configuration. This fact makes the single plane crankshaft the preferred choice for racing V-8’s despite the less than ideal vibration and secondary imbalance.