Constant or Ported Vacuum Source for Distributors? ...AGAIN!
EFI systems with electronic advance ignition use manifold pressure (MAP). They also have 3D timing maps, where timing is controlled in a table of RPM, vs MAP. The 3D advance table, typically has low advance values when RPM is low, and MAP is low. That is similar to when ported vacuum is off when throttle closed, with significantly more ability to adjust... how much, and where in the table. With engine temperature related timing control, and 3D advance, an engine can be tuned with precision for all operating dynamics. Getting such a tune with mechanical distributors and lack of ported vacuum ...no way.
EFI systems with electronic advance ignition use manifold pressure (MAP). They also have 3D timing maps, where timing is controlled in a table of RPM, vs MAP. The 3D advance table, typically has low advance values when RPM is low, and MAP is low. That is similar to when ported vacuum is off when throttle closed, with significantly more ability to adjust... how much, and where in the table. With engine temperature related timing control, and 3D advance, an engine can be tuned with precision for all operating dynamics. Getting such a tune with mechanical distributors and lack of ported vacuum ...no way.
