It is probably just a cam difference, and AF map change between the two motors. Anyone have any hard evidence what exactly are the differences? I would guess that if you got Hondata, and a new camshaft, that the vtec-e motor would work just as well as the regular vtec. i-vtec is on both rsx and civic si models. The i-vtec utilises an adjustable cam timing as well as the different cam lobe profiles. The EP3 civic's vtec lobes are activated a different way, and are more mild than the rsx's k20a2, and so don't preform as well.
Back to the vtec-e, does anyone know if the valves are the same size, does the head flow less, etc? Just trying to help this guy out.