thanks Mike makes a lot of sense.The only 4 plug head I've seen is only the z18. I didn't know they made 4 plug heads for the z20,22,and 24. that's real interesting though. I've never even come across something like that on the net that the came stock with 4 plug head from the factory. but makes sense that they only have it Europe. or do they have it in Australia as well? are all NapZ heads interchangeable to fit z24 block?