The engine design is still being used today in Top Fuel dragster and funnycar class drag racing today.
Sorry about stealing this thread Polo612
The hemispherical head design was revived in 1964. These were the first engines officially designated
Hemi, a name Chrysler trademarked. All Chrysler Hemi engines of this generation displaced 426 cu in (7 L). Although just 11,000 Hemi engines were produced for consumer sale due to their relatively high cost and poor street-use reputation, the engine became legendary, with "Hemi" becoming one of the most familiar automobile-related words in the United States. The 426 Hemi was nicknamed the "elephant engine" at the time, a reference to its large dimensions. Its 10.72 in (272.3 mm) deck height and 4.80 in (121.9 mm) bore spacing made it the biggest engine racing in NASCAR at the time.
The first 426 Hemi of the 1960s was the
NASCAR stock car race engine, introduced in a
Plymouth Belvedere in 1964. Chevrolet had been highly successful in NASCAR after introducing their 409 cu in (6.7 L) V8 in 1961, and other manufacturers were willing to build larger engines to remain competitive. In 1963 NASCAR limited engine displacement to 427 cu in (7 L), and the 1963 Chevrolet 427 "Mystery Motor" was very successful. Chrysler had to do something radical to regain their racing prominence.
There is an old racing expression: "Win on Sunday, sell on Monday", which alludes to when a particular make of car wins a popular race, the manufacturer will sell more of that car to the public. Although all manufacturers were familiar with multi-valve engines and hemispherical combustion chambers, adding more valves per cylinder, or designing the complex valve train needed for a hemispherical chamber, were expensive ways of improving the high-RPM breathing of production vehicles. By canting the angle of the NASCAR-mandated two valves per cylinder, significantly larger valves could be used. With an
oversquare 4.25 in (108.0 mm) bore and 3.75 in (95.3 mm) stroke like the
big-block Chrysler RB, this new generation Hemi was an immediate success, earning recognition when it placed first, second, and third in the 1964 Daytona 500 race. This engine's dominance in a field artificially limited by the sanctioning body led the series organizers to double the number of homologation engines required to be offered to the general public to qualify as a "stock" part, from 500 to 1,000. This eliminated the 426 Hemi's availability for the 1965 season, but Chrysler managed to sell enough Hemi engines to the public to regain use of the Hemi for NASCAR in 1966 in their new
Dodge Charger. David Pearson, driving the #6 Dodge Charger, won the NASCAR Grand National championship in 1966 with 14 first-place finishes.
The 426 Hemi also proved to be an immediate success in
NHRA drag racing. Its large casting allowed the engine to be overbored and stroked to displacements unattainable in the other engines of the day. Top-fuel racing organizers still limit the bore spacing and other dimensions to the 1960s hemi size, making it the de facto engine template. Engines with larger dimensions, such as
Ford's 385-series, are banned under these dimensional restrictions. In NHRA top fuel racing, the Hemi was usually equipped with a large
Rootes type supercharger and short individual exhaust pipes, and fuelled with
nitromethane.
The 426 Hemi, in "street Hemi" form, was produced for consumer automobiles from 1965 through 1971, and new
crate engines and parts are available today from Chrysler. There were many differences between the Hemi and the Wedge-head big-block, including cross-bolted main bearing caps and a different head bolt pattern. There were also many differences between the racing hemis and the street hemi, including but not limited to compression ratio, camshaft, intake manifold, exhaust manifold and carburetion.
The street Hemi version was rated at 425 bhp (316.9 kW)(Gross) with two Carter AFB
carburetors. In actual
dynomometer testing, it produced 315 rear-wheel HP in purely stock form
[1]. Interestingly, Chrysler's sales literature
[2] published both Gross and Net HP ratings for 1971 (425 Gross HP and 350 Net HP.) Assuming a 15% driveline loss, the 350 Net HP figure (at the flywheel) equates quite well with the aforementioned 315 rear wheel HP figure. These power figures are further supported by plugging vintage 426 Hemi road test trap speed data into Hale's Trap Speed formula, which is: Peak Flywheel HP = (Trap Speed/234)^3] * Race Weight. While urban legend might have us believe otherwise, there is no objective evidence to support the notion that the 426 Hemi's advertised output was "under-rated" by Chrysler Corporation.
The engine could produce much higher HP figures with relatively few modifications, but those modifications drastically affected the engine's drivability on the street as they usually were made to take advantage of the free-breathing nature of the cylinder heads at high engine speeds.
To avoid confusion with earlier (1951-'58) and current Hemi engines, the 426-based Hemi is sometimes called the "2G" or "Gen 2" Hemi.
[3] The easiest way to identify a 2G Hemi: A distributor at the front.
The street version of the 2G Hemi engine was used (optionally, in all but the last case) in the following vehicles:
