Not really related to any specific Championship, so I thought I'd pop this in a thread of it's own.
Not as much technical detail as I would like, but a close look around the M-Sport built "RX43" rallycross Fiesta, as used by Block in the GRC and for various gymkhana clips:
https://www.youtube.com/watch?v=Z9v3-DMFyIs
Video includes a lot of rev-limiter bashing and some excellent exhaust flames.