If you love cars, then you must have heard of the HEMI engine. If you were born in the 1960s or before, you remember the phenomenon created by Chrysler HEMI engines in the 1950s, 60s and 70s.
If you love muscle cars or drag racing, you know that the 426 HEMI engine is a popular engine for its power and efficiency. You’ve probably also heard of the HEMI engines that Chrysler started using in 2003 Dodge trucks.
But even if you know little or nothing about cars and engines, the word “HEMI” can still mean something to you. The word has become synonymous with large, bulky, powerful engines. In this article, you will learn about the HEMI engine and find out why engines using the HEMI design are so cool.
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Creation of the HEMI engine
The HEMI engine for automobiles was born in 1948 – Harry Westlake and several others developed the 6-cylinder Hemi engine for Jaguar. A few years later, in 1951, Chrysler introduced the 180 hp HEMI V-8 engine on several models. The Chrysler HEMI engine has a displacement of 5.4 liters and is therefore known as the “331 HEMI” (331 cubic inches).
180 horsepower sounds like nothing these days. But in 1951, 180 horsepower was unheard of. It was an amazing amount of power put out by the engine.
Chrysler continued to refine the HEMI design, with a 5.8-liter (354 cubic-inch) design in 1956, a 6.4-liter (392 cubic-inch) design in 1957, and eventually a 7-liter (426 cubic-inch) version in 1964. year. The HEMI 426 became a legend when it placed first, second and third in the 1964 Daytona 500 NASCAR. 426 HEMI produced 425 horsepower in 1965. The block and head of the 426 are still in production and available to this day.
Comparison of HEMI with other engine designs
What allowed the 1951 Chrysler HEMI to produce so much more power than other engines of the time was the efficient design of the combustion chamber.
In a HEMI engine, the top of the combustion chamber is hemispherical, as seen in the image above. The combustion area in the head has the shape of half a sphere. In a HEMI head, the spark plug is located at the top, center of the combustion chamber, and the valves open on opposite sides of the combustion chamber.
Most engines prior to the 1950s used the so-called bottom-valve flathead because it is easier and cheaper to make. In a flat head engine, the valves are in the block instead of the head, and they open in a chamber next to the piston.
This design is extremely simple – it is a solid metal casting with a drilled hole for installing a spark plug. The camshaft in the block acts directly on the valve stems to open them, eliminating the need for tappets and rocker arms. The problem with such designs lies in its thermal efficiency, which we will discuss next.
Advantages of HEMI Engine
Heat is one of the factors that creates pressure in a cylinder, so heat loss means lower peak pressure. This is one of the key advantages of a HEMI head over a flat head engine. Large surface area causes heat loss. Fuel that is near the walls of the head can be so cold that it will not burn efficiently.
With a lower valve scheme, the value of the surface area relative to the volume of the combustion chamber is large. In a HEMI engine, the surface area is much smaller than in a flat head, so there is less heat generation and peak pressure can be higher. Also, one of the advantages of the engine is that it is extremely reliable and the only thing it needs is to buy good quality engine oils.
Another factor is valve size. Because the valves are on opposite sides of the combustion chamber, there is more room for them. The pre-HEMI engine design was a wedge-shaped combustion chamber with valves in line, and this limited valve size. In a HEMI engine, the valves can be large, which gives an advantage in filling the cylinders with an air-fuel mixture.
Disadvantages of HEMI Engine
If HEMI engine have all these advantages, why don’t all engine use hemispherical heads? This is because there are even better configurations available today.
One thing a hemispherical head will never have is four valves per cylinder. The valve angles would be so crazy that it would be almost impossible to create a head. Having only two valves per cylinder is not a problem in race cars or NASCAR because they are restricted by the racing regulations in those categories. But outdoors, four smaller valves allow the engine to breathe easier than two large valves.
Another reason most high performance engines no longer use the HEMI design is the desire for a smaller combustion chamber. Small chambers further reduce combustion heat loss and also reduce the distance the flame front must travel during combustion.
What cars with a hemi engine?
The Dodge HEMI engine builds on the tradition of the 5.7-liter HEMI V-8. The engine produces 345 horsepower and compares very favorably with other gasoline engines in its class. For example :
- Ford 5.4-liter V-8 – 260 hp at 4500 rpm
- GMC 6.0 liter V-8 – 300 hp at 4400 rpm
- GMC 8.1-liter V-8 – 340 hp at 4200 rpm
- Dodge 8.0 liter V-10 – 305 hp at 4000 rpm
- Ford 6.8 liter V-10 – 310 hp at 4250 rpm
The Magnum HEMI engine has two valves per cylinder as well as two spark plugs per cylinder. Two spark plugs help solve the emissions problems that plagued earlier Chrysler HEMI engines. Two candles initiate two flame fronts and ensure complete combustion.
