Timing/installing a Surefly magneto on a Piper Cherokee 6, PA32-260.
The Surefly SIM is installed at the 0 degrees or TDC of compression stroke unlike the regular magneto, which is installed at 25 degrees BTDC.
At TDC, if the SIM is set for timing advance, (vs fixed timing which is controlled through some dip switches inside the unit) the SIM controls when the magneto fires based on manifold pressure (with a connection to engine manifold pressure source) and up to 38 degrees spark advance.
