Ford started out as speed density but the problem was thier software could only work off set in stone parameters. For example a 302 could only move a maximum amount of air based of x camshaft, y intake manifold and z head. Mess with any of the above and the ecm could not calculate properly because the inputs were off the preset tables. Mass air changed that. A large portion of the oem's went to mass air as they could move to sequential instead of batch fire for fuel and emisions much easier.