Was Raditz faster than the speed of light? In one English dub (there are at least 3 IIRC), Piccolo says Raditz it's faster than the speed of light. But in the spanish dub, he doesnt say so. How about the original japanese dialogue and the manga? Does Piccolo say Raditz it's faster than the speed of light? Was Raditz faster than the speed of light?
Raditz being FTL was a dub fabrication, it is not present in the original manga.
However i noticed that this question has been discussed on various forums and each of them concluded that one shouldn't expect any realism from a non-science based show (though they said this in a lot less polite manner).

Source- http://www.killermovies.com/forums/archive/index.php/t-527409-lightspeed-in-the-dbzverse.html

Discussions-


https://www.neoseeker.com/forums/88/t2273700-raditz-moving-at-speed-of-light/
https://comicvine.gamespot.com/forums/dragon-ball-universe-1775304/raditz-vs-speed-of-light-1747635/