d15 questions...

Not sure if this is in the right forum but whatever. What is the differences in the d15's? I keep reading about d15a(insert number) and d15y, what is the differences in the a,y and whatnot after the engine code? Is it different heads? Any info would be appreciated, as this is how I am learning...

maybe emissions issues, more power, or from other countries.

yup, and year that the motor was made too. Check out this for a basic guide (there are better ones with more motors listed, just search for it on AF): http://www.integra.orcon.net.nz/engines