An engine produced by the Chrysler Corp. in the late '60s and early '70s. Chrysler took their 440 cubic inch motor and swapped the 1 four-barrel Carter carburetor with 3 two-barrel Holley carbs which became collectively known as the "six pack". Other upgrades were also made to the motor. The engine was officially rated at 390 bhp/490 lb-ft. but, like many other big block engines of the time, it was underrated. It was featured in the Road Runner, GTX, Superbird, Super Bee, Coronet, Charger, 'Cuda, and Challenger.
That 440 six pack Road Runner just ate that Hemi 'Cuda up for dinner.