“When we got the green light to go ahead and adapt the hemi head to the big B engine, we realized that one day it would be something revered, that it would be something that everyone would look back on as something very special indeed.” — Tom Hoover Chrysler made their first engines with hemispherically-shaped combustion chambers in the 1951 (following their aircraft engines), but these early motors ranged from 301 to 392 cubic inches).
Steve Boelhouwer wrote that there were 741 “race Hemis” in B-bodies in 1964-67, and 155 in 1968 ’Cudas and Darts.The cost effective way to make a real impression at Daytona was to take advantage of the A311 Indy program background, and adapt it to the race ‘B’ engine.” When the 426 Hemi was introduced in 1964, it was strictly a racing engine.On February 23 of that year, four Hemi-powered Mopars swept the Daytona 500, finishing 1-2-3-4.Chrysler didn’t throw in the towel on the hemi after this (although they did sit out the 1965 season), and the Street Hemi soon showed up in 1966 B-body Dodges and Plymouths.(There was still a race version; a December 16, 1964 service bulletin, showed the 1965 Plymouth Belvedere with the “Super Commando 426,” rated at 425 hp @ 6,000 rpm and 480 lb-ft at 4,600 rpm with 12.5:1 compression.) The hemispherical chamber, as the name implies, is a portion of the sphere. With this we can bring the spark plug into the center of the chamber, which is an excellent position for the spark plug [and allows] excellent breathing of the air past the valve seat.