If they RX8 has separate low & high beams, it's not using H4. However, you might still be able to use them, you just wouldn't have brights anymore. The HIDs are so bright that you might not need them. I know MP3TLH (Kurt) had only the low beams & he swapped them out for low & high. If you have the $$, I think it would be better to get both, but if your dad has the hookup, I'd try it out.