Hemispherical combustion chambers date to the early years of internal combustion engines, and provide excellent thermal efficiency and power production, especially in a relatively long-stroke, low-revving engine. The first two generations of Chrysler engines, called the HEMI are legendary for their raw horsepower and hot rodding capabilities. They are also very receptive to supercharging. The combustion chamber is the area between the piston and the cylinder head in which compression and combustion takes place. Most early racing engines were, by today’s standards, long-stroke and low-revving, and many were supercharged. Hemispherical combustion chambers were commonly used in racing engines built up to the mid-1960s, when the success of the Ford-Cosworth DFV Formula
Chrysler first built an engine with hemispherical combustion chambers in the World War II era, for fighter aircraft. In 1951, Chrysler joined the postwar horsepower race with its first series hemi” V8 engine, and the design became associated with to the company, at least in the public eye. The Chrysler Hemis were expensive to build, and to buy, and low sales led to discontinuation after 1959. (Note here that “HEMI” all uppercase is a Chrysler trademark and applies to the current engine).
But performance made a comeback in the 1960s, and Chrysler needed an extra edge on the competition in Nascar (stock car racing). And so the now-legendary second generation 426 cubic-inch Hemi was born. It won its first race, the 1964 Daytona 500, by a big margin, Richard Petty lapped the entire field. But it wasn’t quite a ‘stock’ production engine, and so was banned – until 1966, when it became available in street form to anyone with the extra cash to buy one. And it took plenty – the Hemi was a $600 to $800 option in cars that cost $2,500 to $4,000. In the late 1960s,
Hemis were nearly invincible in stock car and drag racing during that period. But after 1971, the 2nd generation Hemi was discontinued, at least as a street engine, a casualty of emissions requirements that were far beyond its design specification. It lived on in drag racing, where it and its derivatives dominated the top classes to the present day. As mentioned, hemispherical combustion chambers are friendly to supercharging – and Top Fuel drag-race engines are supercharged to enormous pressure, enough to make something like 5,000 horsepower from 500 cubic inches. (Note that last very very long)!
The next generation of HEMI’s came to life in 1993. Although not the same engine that captured the attention of thousands of kids and racers, but a new, computerized hi efficiency engine. It is not even close to the raw unadulterated power the original HEMI made , but it brings lots of people back to their youth. The original HEMI engines are still available, trust me, they are hard to find. GotEngines.com is an engine specialty supply company, in order to service all engine replacement needs, they have access to used HEMI engines and rebuilt HEMI engines of all configurations.
It all boils down to one thing. Find someone with an original HEMI and go for a ride. That is the proof, and if you are like me, you will never get over it.