After a five year hiatus from passenger cars the hemispherical engine is revived-in the second generation (G2) by Chrysler in 1964 and is sold as “The Hemi” which is now a trademark of the corporation. This newly released 426 cu in engine is large and heavy as well. It comes by the moniker of the “elephant’ honestly. The engine has a tall deck-at 10.72 inches (272.3 mm) with bore spacing of 4.80 inches (121.9 mm) and formidable width as well, a large engine compartment is needed to accommodate the size. This power plant is also pricey by comparison for the day so there were only 11,000 of them manufactured. The Plymouth Belvedere raced with this engine under the hood on NASCAR circuits in 1964. I n 1965 the engine was not allowed on NASCAR circuits because there were too few units available in showrooms. The engine became more widely available to the public for the 1966 model year when the street version is introduced which allowed the power plant to again be seen on NASCAR tracks.
The complexity of the valve train makes this hemispherical engine expensive to produce but it does improve the power plants high RPM respiration in any production automobile. NASCAR mandates only two valves are allowed in each cylinder but by increasing the angle of the valves in relation to the piston the valve size can be increased significantly. The configuration also allows room for additional valves to be added.
The 426 hemi is oversquare; the bore is 4.25 inches with a 3.75 inch (95.3 mm) stroke which immediatly made it a desirable power plant for the NHRA drag racing tracks. It is also an easy engine easy to bore to sizes unattainable with other blocks of this time period, Stroked and blueprinted this is the engine to best in all segments of funny car and top fuel racing. The track version often has a roots supercharger mounted on the intake, duel exhaust pipes, and can be powered by nitromethane.
The street hemi 426 engine was widely available for most high performance and high end Dodge or Plymouth models from 1965 until 1971. The engine was also available as a power option for the Dart in the 1968 model year if you could afford it although this car was not street legal. There was a prototype also made called the Monteverdi Hai 450 SS with the 426 hemi under the hood. The car was built to be in direct competition with Lamborgihini, Ferrari, and Maserati. The original production called for 49 units to be built when unveiled at the Geneva Motor Show in 1970 but production was halted after only two units were produced. The street hemi is much different than the conventional wedge headed big block version including the main bearing caps and the bolt pattern of the heads. The racing 426 hemi and the street edition sported different compression ratio, camshaft, both intake and exhaust manifolds as well as many lesser parts are also not the same. Some of the racing units in the ‘60’s integrated magnesium cross-ram air intakes and magnesium oil pans for the dry sump oiling system in an attempt to cut down the overall weight. Most aftermarket parts today-including pistons, con rods, heads and blocks are often made of aluminum.
Out of the showroom the 426 would produce 425 bhp (316.9 kw) gross and develop 472 lb-ft (640 Nm) of torque although real world testing rate the engine as producing 433.5 hp. The sales brochures in 1971 give the gross 425 hp (317 kw) with the net figures of 350 hp (261 kw) shown as well.