How Does A HEMI Engine Work?

What is a HEMI Engine?

Even if you’re not familiar with engine types, by now you’ve more than likely heard of a HEMI. Remember the old commercials where someone would ask, “Hey does that thing have a HEMI?”, or at the very least you may have noticed the silver letters on the side of a vehicle you were next to at a red light that read HEMI.

Lately there has been a lot of talk about the HEMI engine primarily because of the Dodge Challenger and Charger Hellcats, but you may be wondering what a HEMI engine is, and we are here to explain what it is, and how it works.

HEMIs have a reputation of being big, strong, powerful engines which are the primary characteristics of trucks and muscle cars. Looking back to 1948, the HEMI was created, and in 1951 it was able to produce 180-horsepower which was shockingly powerful for this time period. As the years went on, Chrysler tweaked, modified, and increased the size of their almighty engine.

It wasn’t until 1964 that its popularity spread like wildfire when the 7L 426-cu.in. version took first, second, and third place in the Daytona 500 NASCAR race. At this point, the street version could crank out 425-horsepower, but what made this amount of power possible?

What’s unique about a HEMI engine, and what gave it its name, is the combustion chamber on top of the engine that is hemispherically shaped. Going back in time again to the 50’s when most of the cars used a “flat head,” it was entirely different to see Chrysler create an engine with “hemispherical heads.”

A flat head engine is cheaper, and easier to manufacture (used in most lawnmowers actually) because the valves are on the engine block, and open in a chamber next to the piston compared to the HEMI head where the spark plug is on top of the combustion chamber so the valves open up on separate sides of the chamber.

Without becoming overly complicated, this is one of the primary differences, that and the smaller surface area helps the HEMI keep fuel warm which in turn creates more pressure in the cylinder. The bigger the valves, the greater the airflow which is crucial for horsepower.

Fast forward back to present time to where Dodge now has the legendary 6.2L HEMI V8 that is the creator of the 2015 Challenger Hellcat’s roar.