old emaxx to new emaxx

i am converting my old black frame emaxx to a gray frame emaxx,are the 14 volt motors the same as the 16 volt motors and what pinion should i use on the 14 volt motors they have 18 on them right now and it seams a little slow i am used to the 2 speed tranny,onyone convert the steering on the new emaxx to 1 servo instead of 2 and what did you do