All about the famous HEMI engines

The HEMI motor is an internal combustion engine with hemispherical combustion chambers. The name of this power unit comes from the English "hemispherical" - "hemispherical".


Initially, this technology was used by Chrysler, and the manufacturer himself positioned it as focused on motorsport: most often, HEMI V8 engines can be found on powerful sports cars. These motors are considered sporty due to the peculiarities of their design. Thus, the angular arrangement of the valves, rather than in the same plane, makes it possible to increase the size of the valves themselves, thereby improving ventilation of the combustion chamber and significantly increasing the power output. In addition, the suction capacity of the motor increases: due to the special design, the channels of the fuel-air mixture are less curved, due to which the resistance of the mixture flow decreases.

HEMI motor construction

The HEMI power unit differs from a conventional V8 engine primarily in its design: the upper dome of the combustion chamber of the cylinder is made in the form of a hemispherical dome, on which a spark plug and two valves are located. In this case, the lower surface of the combustion chamber is formed by a piston with a flat surface. This is a fundamental difference from other engines in which the combustion chamber has a cylindrical shape, with a flat surface of the upper arch and piston.

It is worth noting that HEMI engines have a number of features that can be ranked as disadvantages. Among them - a more complex cylinder head design due to a complex valve drive mechanism, and some difficulties in achieving high compression ratios due to the increased height of the combustion chamber. And also the fact that power units are more demanding on fuel and the cost of their production is much higher. In addition, they are almost a quarter heavier than other motors, more toxic and gluttonous. But there are also advantages, in addition to those listed above - the HEMI engines work quieter, and the vibration level is noticeably lower. Although it is worth noting that HEMI engines, due to their shortcomings, have not received mass distribution.


It is worth noting that initially the Chrysler company used the HEMI power unit for the P-47 Thunderbolt military fighters: those engines had 16 cylinders, a V-shaped layout and a capacity of 2, 5 thousand horsepower. Later, in the early 50s, 8-cylinder engines with hemispherical chambers appeared on the sports cars of the Chrysler brand, and then on the Plymouth. Cars with HEMI have won numerous victories, including in the Daytona 500, INDY 500 and NASCAR races. In the latter, by the way, such motors even had to be banned in 1965.

HEMIs were actively used in drag racing: the engine was slightly modified, for example, an aluminum two-plane four-chamber intake-coffered intake manifold was used. Later, this manifold was made of magnesium, and in order to reduce the weight of the engine, the cylinder heads were made of aluminum. An interesting fact: all HEMI power units were covered by a 1 year warranty, while conventional engines were covered by a 5 year warranty. Moreover, if the car took part in drag races ("was subjected to extreme loads"), then the warranty was canceled.

But HEMI engines were also installed on ordinary city cars - this "road" version of the engine was called "Street HEMI". The Street HEMI cylinder heads were made of cast iron, and the engine itself had a lower compression ratio compared to racing versions. The HEMI installation was a rather expensive option at that time - its price was one thousand dollars. But such a motor could work with both a manual transmission and an automatic transmission.

Throughout its existence, the HEMI engine has been modified and changed. So, at the end of the 60s, the power unit was equipped / vktuning with a camshaft with a slightly increased stroke, and due to some modification it was possible to reduce oil consumption.

HEMI engines have been installed in cars such as the Dodge Charger, Dodge Super Bee, Plymouth GTX, Plymouth Barracuda, Plymouth Roadrunner, as well as the relatively modern Chrysler 300c HEMI V8, Jeep Grand Cherokee 5.7, Grand Cherokee SRT8 6, 4 and Dodge Challenger.

Interesting facts from the "biography" of HEMI:

The first engines with hemispherical cylinder heads appeared over 100 years ago.

The cost of a HEMI engine in the middle of the 20th century was one third of the cost of a car.

In 1991, a car with HEMI set an absolute speed record in the Supercharged class, accelerating to 659 km / h.