This forged 5140 steel 4.00" stroke crankshaft is the highest quality GM offers for big-block V8s. It is nitride treated to increase its hardness and fatigue strength. The main bearing journals are cross-drilled to provide a constant supply of oil to the rod bearings. For use with Mark IV design engines only. Technical Notes: This crankshaft is externally balanced. It must be used with a counterweighted torsional damper and flywheel (or flexplate) for correct engine balance. Main journal diameter is 2.75", rod journal diameter is 2.20". Crankshaft ID is #3521.