aight heres the deal the f23a1 is the vtec and so is the f23a4 although the f23a4 is the ulev(ultra low emissions vehicle) thats also what i got in my car

the f23a1 has 150 hp and the f23a4 has 148 not much a difference thank god

check out this website for more engine codes
http://www.torontoracing.ca/video/tech_hndacodes.html