There’s a famous advertising catch-cry in North America: `Yeah, it’s got a Hemi’. And that five-word phrase was enough to gain the attention of performance-car lovers in no uncertain terms.
But what is a Chrysler Hemi engine and why is it so special?
Actually, that’s not exactly a simple question to answer, because there have been, in effect, four engine series from the Chrysler family that have carried the Hemi marketing tag. And one of those was an Australia-only family of powerplants.
Meantime, what is a (lower case `h’) hemi engine? It all comes down to the shape of the combustion chamber; the space in the engine where the air and fuel actually burns to create torque which is the force that turns the crankshaft and, ultimately, the car’s wheels.
And what does Hemi mean? Basically, that this combustion chamber is shaped like half a tennis ball, or roughly hemispherical, hence Hemi. That places the spark plug roughly in the centre of the combustion chamber for good flame propagation and allows for a large intake and exhaust valve (bigger valves mean more air and fuel in and out).
The cross-flow design where the air and fuel enters on one side of the combustion chamber and exits on the other side) also helps with overall efficiency.
Chrysler is by no means the only carmaker to have used a hemispherical combustion chamber, but thanks to the magic of marketing, it’s the brand that has become most closely associated with the layout.
As early as 1907, Fiat had realised the potential of the hemi design and had taken it to race tracks with its Grand Prix car.
Interestingly, the advent of multi-valve cylinder heads has slowed the production of engines with the hemispherical design as it lends itself better to two large valves rather than four smaller ones.
But lots of manufacturers over the years have used a hemi design, even if they’ve not referred to it as such for fear of giving Chrysler a free kick.
In Chrysler’s case, the first engines to use a Hemi layout were a pair of engines designed for military use in a tank and a fighter plane.
The end of the war and acceleration of the jet age killed off both projects, but Chrysler engineers could see the benefits of the tech and used it for a family of car engines that went on sale just a handful of years after World War 2.
That first-gen Hemi V8 was built from 1951 to 1958 and represented Chrysler’s first production overhead valve V8s. The line-up started with the 331 cubic inch (5.4 litre) ‘FirePower’ and ‘FireDome’ engines which eventually grew to the 392 Hemi (6.4 litres).
But better was to come. That arrived in 1964 with …….