The 340 was introduced in 1968 and immediately began building its reputation as one of the most popular and best performing engines available. Many heavy duty parts were produced for the 340. The heart of the 340 is its big port, high flow cylinder heads and well designed,180 ° 2 level intake manifold. Even though most 340 engines used 4-BBL carburetors, the production 'A' engine reached its highest performance equipped with the 1970, 340 6-BBL T/A package. This engine used a special thick web block, specially machined heads, adjustable rocker arms, and a unique carburetor and intake manifold setup. In 1970 the 340 lost its 10.4:1 compression ratio in favor of an 8.5:1 for emission reasons. It also picked up the 360 head with the smaller intake valve. Production of the 340 ceased at the end of the 1973 model year.