[bobcowan]

Most SBF's are externally balanced. Meaning that the extyra weight is added to the blancer AND the flywheel. Early engines add 28oz to balancer and flywheel; later engines use 50oz.

Some custom engines will be internally balanced. And then the harmonic balancer and flywheel do not have weights attached. Internally balanced engines add Mallory metal to the crank throws if needed, or metal is drileld out of the crank throws.

Balancer and flywheel weights need to match the crank.

The crank is balanced dynamically - spinning. Bob weights are usually attached to the crank throws to simulate the weight of the reciprocating assembly.

Clutches and transmissions are generally not balanced, except in extreme rpm applications.

Any time the engine is tressed - regardless of rpm - then balancing becomes more important. It's a time consuming and tedious process, but worth the effort for racing.