I have a 6-71 blower on a small block Chevy and keep having trouble breaking the harmonic balancer. What can I do to keep this from happening again?

When you go to a large blower like a 6-71 or larger it is a MUST to have the crankshaft cut with a double keyway and run a steel SFI double keyed harmonic balancer (not a fluid filled balancer).The stock cast balancer with the combination of the small single key in the crank will not hold up to the torsional load applied to the nose of the crankshaft from the superchager. The engine should be built for a blower this large any way and should already have a steel crankshaft.