55* total timing? WTH?

There's two methods of mapping a dizzy curve, one using ported vacuum and the other using manifold vacuum.
A ported vacuum setup could be mapped 18* initial, 16* mech, 16* vacuum, total 50*
A manifold vacuum setup could be mapped 6* initial mech + 16* vacuum, 28 mech, total 50*
When using the manifold vacuum port an adjustable canister let's you move the curve + or - to fine tune to what the car likes without pulling the dizzy.
Most open chamber heads like higher initial timing settings.