Bill is right on with his comments about the thermo reactors. But I will add what the changes were to make it a 528i. They did away with the thermo reactors, air pump, EGR, retard only distributor and added an oxygen sensor, a catalytic convertor and electronic ignition distributor. Underhood it is clean, the only visible smog equipment is the dual diagraphm distributor. The net result was a faster(even if it had less rated power) car that was cleaner, got better mileage and lasted much longer. Mike W.