what exactly is the diferense between the 83 1.8 outa my is and the 79 2.0 i got?are the blocks or pistons or cam , heads or any of that the same?anybody please post the diferences! thanx

This should answer your questions:

http://www.bmwe21.net/e21/us320i/

what im trying to find out now is what can i put from my 2.0 motor into my 1.8 motor to make more power.like crank rods/pistons,cam,intake minifold???? what do i need to put in it to bump it up a little. and most of all i dont want to have anything on the 1.8 milled or bored. so if anyone knows please get back to me. thanx

Not sure I fully understand your situation. Why don't you use the entire 2.0 engine (with the old cam & distributor if I have read things correctly)?

Why would you go to the extra time and labor of trying to swap crank, rods, pistons, etc. over to the 1.8 (and then wouldn't the head volume be off) when you can use the 2.0? If it needs to be rebuilt, then rebuild the 2.0 and install that when it is done - should reduce down time as well.