John Dianna(SP?) modified production 1971 duster, which later became a 1973 and 1974 Duster G/G car ran the Moldex (I think that was the brand) 2.96 inch destroked cranks from the road race program. He told me he would let the clutch out around 8600 RPM and shift at 8800 RPM, this was back in 1975 and pre 1975. New technology would probally raise that to or higher than 9000 RPM with the same block and heads, NASCAR motors have been over 11500 RPM