Since number 3 said the largest engine ever in an A body and didn't specify street production, I went with the 426 Hemi.
Also in 1968, Chrysler made approximately 50 fastback Barracudas equipped with the 426 cu in (7.0 L) Hemi for Super Stock drag racing.[2] These cars were assembled by Hurst Performance and featured lightweight items such as lightweight Chemcor side glass, fiberglass front fenders, and hood with scoop, lightweight seats, and sound deadener and other street equipment such as rear seats omitted. An included sticker indicated that the car was not for use on public roads; it could run the quarter-mile in the mid-10s in 1968.[2]
