Thank you to all the people who replied, some good experiances here. I guess I'm just going to have to experiment.

I happened to check my owners manual today and it recomends Bosch W9DC or W9DP. However I cannot find W9DP's anywhere. Boschusa.com recommends:

WR9DP Platinum resistor plug
4479 Platinum +4
4307 Platinum 2
W9DC Super Plug copper
W9DC0 O.E. spark plug
7511 Super part
4220 Platinum Part

Has the W9DP been droped from poduction? It seams to be banished from the face of the earth.
How can I tell if the 4 diget code Bosch plugs are resistor plugs or not? I cant find a decoder for this series of plugs.

John Roncallo