F-Zero GX is insanely hard. The game is best enjoyed on the hardest settings, which can be pretty fucking ridiculously unforgiving. Especially if your machine sucks and most them do.
I think some custom machine parts were unlocked that way.
There are also extra machine parts in the game that only have unlock prerequisites in the Japanese version, so you'll have to hack the game to get those.
I see. I guess it's time for me to buy one, then... I usually hate using those, but if there's content that's impossible to get, then I have no choice.