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The big-block engines initially used a forged crankshaft with a stroke of 3.975" for the 1965-1967 425 and 400 CID versions; starting in 1968, both the 400 cu in (6.6 L) and the 455 cu in (7.5 L) big blocks used a stroke of 4.25 in (108 mm), with crankshaft material changed to cast iron except in a few rare cases.
The mechanical supercharger compressor, driven at 5 times the speed of the crankshaft, mainly operates at low engine speeds from idle up to 2,400 revolutions per minute (rpm) to increase low-end torque. At engine speeds just above idle, the belt-driven supercharger provides a boost pressure of 1.75 bar (25.4 psi).