Back in the 2004 before the internet was a staple in everyone’s home and before you could look up your favorite (or least favorite) commercials on YouTube (which started in 2005), a series of commercials was released. The first started with two men at a stoplight in an old muscle car. They pull up and ask the guy in the Dodge Ram next to them at the stoplight if “That thing got a hemi?” After being thoroughly trounced by the Ram which was also hauling a muscle car, a series of commercials was born with each one featuring the iconic, inescapable line “That thing got a hemi?” Though its been well over a decade since these commercials debuted, the question still remains, “What is a hemi anyway?”
Hemi is Short for Hemisphere, and What a Difference a Hemisphere Can Make
To understand the difference between a normal engine and a hemi, we first have to look at the structure and function of a normal internal combustion engine. A typical gas engine (diesel functions differently) runs by first taking in a mixture of gas and air, which is then compressed by the piston and ignited using the spark from a spark plug. The combustion of this fuel forces the piston out again, turning the crankshaft and running the engine. The engines in modern cars have several of these pistons—a basic 4 cylinder vehicle has 4 pistons.
In a simple—non hemi—engine, the chamber that the fuel is injected into has a flat top. This flat top is a much simpler manufacturing choice, but isn’t the most efficient when it comes to burning the fuel. The fuel that is in the corners of the chamber will be cooler than the fuel elsewhere and will not burn as efficiently. This is where the hemi engine comes into play.
A hemi engine does not have the typical flat top as other internal combustion engines. As the name implies, a hemi—or hemisphere—engine has a rounded top, like the rounded hemisphere of a globe or half of a ball. This rounded head chamber takes away the corners, reducing the surface area and making sure that the fuel mixture is as warm as possible for an efficient use of the fuel during combustion. Efficient use of fuel will give you more power when driving at higher rpms.
The Hemi in History: Hemi’s Beginnings in the Racing World
Though the commercial has only been around for a few years, the idea of a hemi engine has been around from almost the beginning, with the first example from 1901, originally designed for use in a boat. It was quickly adapted from there, being used by carmakers as varied as Fiat, Peugeot, and Alpha Romeo in their Grand Prix cars in the early 1900s. It was a straightforward change to get more power out of engines that needed high levels of performance at higher speeds.
Chrysler is known for taking the hemi design and perfecting it over the years, even going so far as to trademark the hemi name in the 90s. Chrysler’s interest and development in Hemi engines has continued for decades. Their first overhead valve V8 with a hemi engine—then known as FirePower—was released in 1950. The engines were refined over the years under various names from the FirePower in Chrysler and Imperial cars, to the Fire Dome in DeSotos, and the PowerDome in early Rams. It wasn’t until the 60s that these types of engines began to be referred to as hemis. The original Chrysler design was improved upon over the years, and its distant hemi relations are still found in the modern Dodge Chargers and Rams of today.
Outside of the Chrysler family, a version of hemi design was used in production cars from carmakers all over the world. Hemisphere type engines have been used in Jaguar XK engines, Lancia V4 and V6 engines, Mercedes M102s introduced in 1980, and Porsche’s flat-6 911 engine from 1963-99.
Why Isn’t It Hemi Time All of the Time? Drawbacks of the Hemisphere Engine
Though it is still common for vehicles such as the aforementioned Ram to have hemi engines, they have been losing popularity, with several car makers discontinuing their more common use around the in the past 20 years. This has to do with some of the more unfortunate drawbacks of the hemisphere engine design.
Though it may be more efficient at burning fuel at higher rpms, this isn’t true at all speeds. Modern non-hemi engines have multi-valve cylinders which allow for better air flow and more efficient combustion in general, with numbers of valves increasing to up to 6 per cylinder. Due to the construction of a hemi engine, there can only be two valves. This decreases air flow to the engine, and decreases fuel efficiency, leaving more emissions than many modern engines with multi-valve designs can achieve with similar power outputs.
In addition to drawbacks connected to power and emissions, hemi engine are physically larger and more difficult to engineer. The angles needed to create seals from the valves in hemisphere engines require more space in the engine and more space underneath the hood.
The Hemisphere Engine: A Tale of Car History and Motorsport’s Past
Though the hemi engine is still used in some circles, when it comes to modern cars, there are many engines who can produce the same power as a hemi engine with a smaller physical footprint, less emissions and more fuel efficiency. While definitely not relegated to a thing of the past—in motorsports racing when cylinders are limited to 2 valves, a hemisphere engine is likely the way to go—it is not necessarily the best choice for new cars for the modern driver.
Does that thing have a hemi? No, but it does have 4-valve cylinder heads, which though they certainly don’t sound as cool, they still make my car pretty darn fast.
