340 CID Small Block Engine
The 340-ci v8 was introduced in 1968 as a high performance replacement for the 273 commando engine. The 340 has a 4.04" bore and 3.31" stroke. It featured high-flow cylinder heads with 2.02" intake/1.60" exhaust valves, dual-plane intake manifold, forged crankshaft and connecting rods with 10.5:1 compression. Cam timing was 268 /276/44 on vehicles equipped with Torqueflight automatic transmissions, and 276/284/52 with manual transmissions.
In 1970 the 340 reached its zenith with the production of the 340 six-pack. This engine was designed for Trans-Am racing was only available on the 1970 Plymouth AAR 'Cuda and the 1970 Dodge Challenger T/A. The 340 six-pack got its name from the three 2-bbl carburetors bolted to an aluminum Edelbrock intake manifold. The engine block was also beefed up with thicker webbing and pan rails to accept new 4-bolt mains. This 340 six-pack motor was rated at 290 horsepower.
1972-1973 340's had compression reduced to 8.5:1 as well as receiving the new 360 cylinder heads with smaller 1.88" intake valves and hardened exhaust valve seats for unleaded gasoline. Performance declined slightly, producing 240 hp at 4800 rpm. In 1974 Chrysler retired the 340 from production and replaced with a high-performance 360-ci v8.