Auto Questions: How Hemi Engines Work

Even the part-time automobile enthusiast has heard the word Hemi. The throaty sound of the new Hemi engines sound like the supped upped muscle cars of the 1960's. How do they work?

If you're even a part time automobile enthusiast, you have heard the word Hemi. The throaty sounds of the Hemi engines make the new trucks and cars sound like the supped upped muscle cars of the 1960's. From the 1964 Daytona 500 winner to the 1966 Dodge Charger 426 to the 2003 Dodge Ram, the Hemi has made a comeback. The powerful 426 cubic inch engine is still available from Dodge, and is used today for drag racing, funny cars and muscle cars.

Hemi is a registered trademark of Chrysler Corporation, and comes from the word hemispherical. The concept of the Hemi engine is a fairly simple one. Instead of having a flat head or a wedge-shaped combustion chamber, the chambers in the Hemi engine's heads are hemispherically shaped. This design allows for a more efficient engine through better thermal cooling, combustion and compression.

The shape allows one to put the intake and exhaust valves in-line, instead of side-by-side, allowing a better air flow through the chamber. It allows for additional smaller valves in some engine designs or larger valves in other designs, greatly enhancing porting.



Additionally, the spark plug is typically located in the center of the chamber in a Hemi engine, creating a better fuel/air mixture. Unburned fuel is wasted energy. This design allows for a more efficient burning of the fuel/air mixture, burning more of the fuel in the chamber on each stroke of the engine.

The hemispherical design does however have limitations. The same design that gives us advantages in placing valves, also limits us to the number of valves that can be installed. If more than four valves are placed on the cylinder, the angle of each valve in relation to the other becomes too complex to effectively manage.

New engine designs allow for smaller combustion chambers, cloverleaf shaped chambers, and pent roof (peaked like the roof of a house) chambers. The goal with all of these designs, including the Hemi, is combustion chambers that allow for an additional number of valves, additional spark plugs, better thermal cooling, all of which produces a more efficient and powerful engine.

The history of the design is clouded, yet it is clear that Chrysler did not create the first hemispherical engine. However, in 1951 Chrysler produced their first engines with the hemispherically shaped combustion chambers. These first vehicles and engines have nothing in common with the modern 426 engine or the Dodge Truck engine design except for the chamber shape, spark plug location and valve location.

In 1964 the 426 was introduced to the world. It was designed and produced for auto racing. That same year, Hemi powered cars swept the Daytona 500, taking first through fourth place. This not only changed the racing world forever, initiating NASCAR to impose limitations, it changed the way world thought about racing engines as well as production vehicles. The consumer's demand for the Hemi was met by Chrysler in 1966 in both Dodge and Plymouth model cars.

Because of its flavorful history, the word "Hemi" still conjures exciting images and emotions of fast muscle cars, and now powerful, affordable trucks. Chrysler has evidently met the consumers' desires again, resurrecting a successful design and implementing it into a modern market, creating once again a very successful product of Chrysler Corporation.

© High Speed Ventures 2011