Is this Chenghou at Elite difficulty or just against novice/skilled?

If it's against novice/skilled then you need to practice speed laps so you get the track memorized, usually barrel rolls alone should give you 1st place as the AI doesn't perform them.

Elite AI doesn't perform BR's either, but they are 15% faster than you around the course [cheating SOB's], so the best tactic is to stay back for the first 2 laps as the Elite AI race relative to your current speed/placing, then go hell for leather on the last 3 laps if it's Phantom speed, and BR at every opportunity and keep tight lines.

Even then it's a bit of a crap shoot till you get really good at this game.

Here's Hellfire's Tutorial on Chenghou, part of a complete series.
http://www.youtube.com/watch?v=6cXntkL-yDc