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Old 03-19-2018, 05:41 AM
joe_padavano joe_padavano is offline
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Actually, the 425 was made from 1965-67. Every one of them has a forged crank. Nearly all were high compression. 4.25 bore, 3.98 stroke. Externally they are dimensionally identical to the Olds 455. Beware that most 425s used a 45 degree lifter bank angle instead of the 39 deg version more common on Olds motors. The cam is different as a result, so be sure you know what you have if you ever plan to get a cam. Head castings were different each year. The 1965 "A" castings used 3/8" rocker studs. The 66-67 heads used 5/16" bolts. All 455 eternal parts (intake, headers, distributor) bolt right on. The 1964-67 Olds motors use a different crank flange bolt pattern than do the 1968-up motors, so flywheel needs to match. Factory ratings were 365-385 HP for 4bbl motors.
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