ddloyd, it seems like a no-brainer to me. Take your Santa Fe in for service to replace your possibly defective spark plugs with new NGK plugs. Ask to check condition of new plugs before they are installed. You'd be crazy for risking your warranty for a possible (and maybe none) gain in a few horsepower. The possible Bosch gain would depend on the current efficiency of the Santa Fe engine and NGK firing as well as settings such as recommended timing. Actually on the Mazda Miata, you can pick up a about 5 horsepower by setting timing up 5 degrees and changing to a cooler NGK plug. Maybe this is also true of the Santa Fe and you could stay with an NGK plug. In any case, if you really want performance and are going to void your warranty anyway, wait a little for a performance computer chip to hit the market for Santa Fe and change to it. Or add a supercharger and really blow your warranty but add performance. To blow your warranty or possibly risk it for a few possible horsepower gained is simply nuts.