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From what I have heard the reduction in journal size on the 70.4 mm crank and the corresponding reduction in torsional stiffness was what led to the torsional harmonic mentioned above moving into the range of engine speeds which were regularly seen by the racing engines. This caused the flywheels to be shed.
I thought I read that the 917 engine had a bad torsional vibration but that this was below the rev range normally used.
Perhaps smaller counterweights can push the torsional harmonic to a higher rev range?
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1971 911S, 2.7RS spec MFI engine, suspension mods, lightened
Suspension by Rebel Racing, Serviced by TLG Auto, Brakes by PMB Performance
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