ddloyd,

Yes, I am a Santa Fe owner. I have a Sandstone 4WD V6 LX. And no, I haven't removed the surge tank to install plugs; I've still got the stock ones in. It hadn't occured to me that it would be necessary.

If your dealer told you that other plugs will void your warranty, they're either lying or stupid. It's illegal for them to pick and choose manufacturers like that. As long as your preferred plugs meet same specifications (heat range, reach, etc.) as the NGK or Champion plugs

NGK V-Groove plugs may be expensive, but, believe it or not, NGK also makes normal, non-platinum plugs. Just like all other spark plug maker (with the exception of SplitFire, obviously). I don't know how much they cost, but they're probably about the same as a comparable Bosch or Champion non-platinum single electrode plug.

Billbo1970 is exactly right. Platinum doesn't conduct as well as copper, which is why ENTIRELY copper plugs (that is, core AND tip) perform better than platinum (platinum tip and copper core) plugs do. Making a plug with anything but a platinum coated tip would be absurdly expensive, as platinum costs more than gold.

Also, Platinum+4 plugs have the performance decrease due to the flame propagation problem.