The Hemi or HEMI V8, trademarked by Chrysler,We have known about the motorcycle for a long time, but where does this motorcycle come from? 

The Hemi gets its name from the hemispherical shape of the cylinder head. Chrysler has been using Hemi's since 1949, but this type of combustion chamber engine appeared much earlier, in the early 1900s. In Europe, Fiat, Peugeot and Alfa Romeo It first debuted in F1 cars. In America, it was introduced in the 1904 4-L model of the Welch Motor Car Co. and was intended to replace side-valve engines. The advantages of hemispherical cylinder head engines in a nutshell: The air does not have to change direction in the combustion chamber, which improves airflow. This makes the engine more efficient, and due to better flushing of the combustion chamber, fewer hotspots develop, thus increasing the life of the engines. Due to its design, higher compression can be achieved, which results in more power. A Hemi has two large valves that are opened by a pushrod..

But nothing in life comes for free. So let's look at the disadvantages:
Due to the hemispherical design, it can only have two valves, otherwise the valves will open together, which would lead to the immediate death of the engine. It is structurally more complex than the flathead types. This means higher production costs and more difficult maintenance. It can only be tuned to one speed range, in contrast to today's VVTI engines. So it is optimized for either low or high speeds. In the case of a sports car, it has a particularly big disadvantage, thaty is approximately 25% heavier than an engine with a wedge-shaped combustion chamberNow close your eyes and imagine the full-throated roar of a Hemi engine at full throttle. That unmistakable sound—a symphony of power and aggression—has become synonymous with American muscle cars.

Many people associate Hemi only with big American cars, and the more educated (or not?) with Chrysler, but in reality many more European brands used the hemispherical cylinder head than Americans. Without claiming to be complete, here are a few examples:

Alfa Romeo: Busso V6 – No, not the 24-valve one, but the original one!

Aston Martin: DOHC V8 – Yes, 5.3L, 4 camshafts, late 60s to late 80s

BMW: M10 – 2002 sports sedan: 2l, 4 cylinder, HEMI

Jaguar: XK – 1949-1992, from the Le Mans-winning D-Type, through the E-Type to the XJ6, sound familiar?

Lamborghini: V12 – Since 1963, for over 50 years, every Lambo V12

Lancia: V4/V6 – Low-angle (10°-20°) V engines, Fulvia coupe? First DOHC? HEMI!

Lotus: Lotus – Ford Twin Cam – 1962 Lotus Elan 

Mercedes: M102 – 1.8L-2.5L almost all! There is an exception: 2.3 16V Cossie, aka DTM 190E

MG: MGA Twin-Cam – Only for 2 years, not the most reliable, but Hemi!

Mitsubishi: 4G1,4G5/4D5, 4G3 – Early 70s, 3 motorcycle families from the Land of the Rising Sun

Nissan: Z, VG – Million+1 in a car

Porsche: 911 – 1964 to 1999, i.e. ALL air-cooled 911 HEMI

Toyota: V6/V8 – From the 1960s to the 90s, most of their longitudinally mounted V engines were hemi