If you have heard of cars, you have probably heard of an HEMI engine. Aside from DOHC and VTEC engines, HEMI engines are the ones that are on the top three of most prized engines.
HEMI started with Chrysler creating the first one back in the 1950s. Muscle cars and drag racers are especially fond of HEMIs because the 426 HEMI is the most popular engine in these cars. HEMI is also now increasingly popular with Dodge who first introduced
them in trucks and then in smaller vehicles such as the Magnum and Charger.
Most people associate a HEMI with power, but not everyone knows exactly what these amazing machines are.
Back in 1951, Chrysler produced the first HEMI engine, which was a V8 with 180 horsepower. Although 180 HP is nothing these days, it was an astounding amount of power in 1951. The engine had a displacement of 331 cubic inches, giving it the name 331 HEMI.
Likewise, the 426 HEMI in drag racers has a displacement of 426 cubic inches, or for those on the metric system, 6980 cubic centimetres (6980 cc). The incredible 180 HP sparked the fire that turned into the “HEMI legend.”
Most people must now be wondering about the difference between an HEMI and a normal engine.
The main difference, and the reason why an HEMI can produce so much power, is the shape of the combustion chamber. The top of the combustion chamber is hemispherical instead of flat. An engine like this is said to have hemispherical heads, resulting in the
name HEMI. The spark plug is located in the top of the combustion chamber, between the valves.
Before the HEMI shape engine, most cars had what was known as a flat head. A flat head engine is cheaper to produce. The valves in the flat head are on the side of the piston, in the block, rather than on top in the head.
Anyways, back to the current HEMI engine. Now what’s so great about the HEMI engine? The idea behind the HEMI shape comes from many theories about getting the most power out of each engine cycle.
First of all, you want to burn all of the gas in the cylinder. And unburned gas is wasted energy. Besides that, you want to waste the least amount of energy as possible by making the engine work as easy as possible and at the right moments. You also want
to lose the least amount of heat as possible, since heat creates pressure, and lost heat equals lost pressure.
Now a HEMI engine solves all of these issues. But if a HEMI has a bunch of advantages, why don’t all engines use them?
Truth be told, there are better engines available.
That’s because the top of the chamber is round. Why does that matter? Well, you can only fit two valves. Even though this is fine for NASCAR and drag racing, where they are allowed only two valves per cylinder, this would increase gas consumption and decrease
performance.
So what do the new HEMI engines use? They use a pentroof design. Instead of having the top of the combustion chamber as a sphere or straight, the pentroof HEMI uses a slightly triangular, or roof shape. At the top of the triangle is the spark plug and, on
either side, valves. This allows up to four valves to be placed on the head instead of just two in a normal HEMI.
Also, most high performance engines wish to create the smallest combustion chamber possible. Small chambers reduce heat loss and shorten the distance that the flame must travel during the combustion cycle.
Now that DOHC, VTEC, and HEMI has been discussed, it is time to take a look at other features that should be considered when looking to buy a new car for auto racing.
Next up is visibility and most importantly, high intensity discharge (HID) headlights.
To be continued…
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