I have been browsing the STR forum and Avos over in Europe has fit a kit to the 4.2, so I messaged him and asked about he possibility for the XF 4.2 and he said it would fit. Just to finalize he would need a car in his possession. Any takers?? There is a whole thread dedicated to his journey with the twin screw. He has already built for the 4.0 guys and now 4.2. The results with the 4.0 is crazy, and have been tested for years with no problems. He has a couple stages he offers. Any where from 100-150 HP with no additional mods. Could possibly get up to 200 Hp with other mods.