Just put a fairly new audi 2ltr bottom end on my 1.8ltr top end for a 87 jetta. now it pings like all hell when it is warm. please help.

Pinging when warm means it's running too lean. I know nothing about Jetta engines, but you can probably adjust your carbs for a richer mixture... a mixtue screw or re-jet them. Maybe post in watercooling section for more detailed answer.

Oh and make sure your timing is correct too...

is this the K jet tronic injection or carby?

more likely your comp ratio is up the shit ,,normally when manufactures increase capacity they increase stroke so by using a 2l stroke on 1.8 heads without relieving the combustion chamber you would have effectivly increased comp ratio about all you can do is run on premium gas and retard it a bit