EVO2 and EVO4 engine are totally different engine...you have different cylinder, rod, bearings...so all the parts are different.
According to me if you are satisfied using an EVO2...you will be really surpriesed when you'll test the new EVO4, standard or STI version, according to me it's one of the best engine made by Sirio, in particular if you use a Sirio or Capricorn clutch system.