The classic Chrysler small block engine reached its performance peak with the 340 cubic inch version in 1968. This "big bore" variation of the classic 318 V8 significantly increased power output while retaining the fast-revving relatively short stroke of its parent. Along with the displacement increase, 340 engines came with four barrel carburetors, performance-oriented intake and exhaust manifolds, large port heads with bigger intake and exhaust valves, and, in most years, forged crankshafts.

Chrysler 340 engines were found in many of the best muscle and ponycars of the era; from Valiant and Dart compacts and their coupe derivatives, the Duster and Demon (or Dart Sport), Barracuda and Challenger, Charger, and Roadrunner. The delivered excellent performance while their lighter weight (compared to the Chrysler big block engines and Hemis) allowed considerably more nimble handling. This is especially true in the lightweight A-body compacts, where 340 Dusters and Demons became street and strip winners with the excellent balance between engine and chassis.

The zenith of 340 performance was the notorious six barrel engine (Six Pack for the Dodge folks) that came with the Challenger T/A and AAR 'Cuda packages. These engines provided amazing wide-open-throttle performance with excellent streetability, and sometimes surprising fuel economy for the day, since they could run on the relatively small center 2-barrel carb if the driver would keep his or her foot out of it (easier said than done!).