Theory and Analysis:S² Engine's Absence in Evangelions

(Rough ideas...got any more?)

S2 engines having to be manufactured and installed by Nerv itself.

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.