I'm not normally keen on one car summits, but I quite enjoyed this one with the Valhalla and some decent tracks.
First tip - for the speed trap, and the race where you have the discrete chunks of nitrous, you want a nitro chemist set with pure and frenetic if you've been playing the game long enough to have an extra set to recalibrate to that. Also make sure you have legend points on cluster, which gives faster times for drag races, as the race with the discrete nitrous chunks is technically a drag race, I think.
Second tip - there are some fairly big cuts, which I think IVT intends the player to take, as I can't see any other reason for the checkpoints to be where they are. 11:25 and 14:10 in Akor's video are two of the biggest ones I'm aware of:
Okay, I have cracked the code of Grand Races. It's a repeating loop of 23 races. I've been recording what every Grand Race was in a spreadsheet, and the first 3 have now exactly repeated, so I assume that will continue. I don't know when the loop changes, I think it will be different for at least one day of the weekend, and might need re-syncing after that. But for now, this is the repeating schedule:
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