Theory and Analysis:S² Engine's Absence in Evangelions
(Rough ideas...got any more?)
Possibilities-
1. Adam and the Angels were already equipped with Super Solenoid engines by the FAR. 2. Angels went through a prolonged gestation period in their eggs, during which time they were capable of generating the engines by themselves, while Evas were built in a shorter timeframe and by a process that did not allow for the engines to be created. 3. Evas do have a limited capacity to generate infinite power, as witnessed by Eva-01 and Eva-02 going berserk, but this power capacity can be used only under extreme duress and is inadequate for creating new life or a Third Impact.