383 CID B Big Block Engine
The 383 B block, or "low block", has a 4.25" bore and 3.38" stroke. The 1966-1967 383 had a 10:1 compression ratio. The standard issue 4-bbl motor had 325 horsepower.
In 1968 and 1969 there were two new high performance versions of the 383 available. The 383 Super Commando was a slight performance upgrade producing 330 hp due to an unsilenced air cleaner and dual exhaust. The best 68-69 383 engine was available on the road runner and coronet superbee. It made, some say underrated, 335 hp thanks to a number of high-performance 440 parts . It received the recontoured 440 heads with larger exhaust valves of 1.74", compared to standard 1.60" exhaust valves. Heavy duty valve springs and rocker arms were also installed and shared the same camshaft as the 440. In addition this engine also boasted a new dual-plane intake manifold with a Carter AVS 4-bbl carburator.
Compression ratios were lowered across the board in 1970. The 2-bbl 383 was now 8.7:1 compression ration to run on regular gas, but was still rated at 290hp. The two high-performance 383s had compression lowered to 9.5:1 but performance ratings remained unchanged. the 335 hp version not sported a Holley 4-bbl carburator.
The 383 big block was further detuned in 1971 to run on regular fuel. There were now two 383s offered a 275 hp two-barrel and a 300 hp four-barrel. Both version had a lower 8.5:1 compression ratio. This was the last year of production for the 383. It was replaced in 72 with the 400 cid v8.