I came across this video where someone shows that it's possible to get platinum with only green parts, and without even using any legend points. This was interesting to me as I'd considered getting a 2nd copy of the game next time it's on sale, to be able to try this on an alt account (the game doesn't support Steam family sharing, so you can't do this without getting another copy).
I think one reason why it's possible to do this well with green parts is the nerfing of nitro chemist sets vs TC2 in 4 ways:
1. Nitro chemist sets give 2x nitro in TC2 vs 1.5x in TCM.
2. You start with a full tank in TC2 vs empty in TCM. The full tank with a nitro chemist set gives you a massive boost at the start of events in TC2.
3. The max affix percentages for pure and extra pump have been nerfed from 8/10 to 5/5.
4. There are no boosted sets in TCM.
I've been grinding parts for planes, and now have every type of plane set, but I only have one nitro chemist set, so have a pure+gateway set but not a pure+extra pump set. The pure+gateway set got me 43rd on this leaderboard:
I've no idea how it's possible to go 11 seconds quicker. Akor and ozfh are on 3:28/9, so maybe the 3:21 isn't legit.
Looks like there's a Street Tier 1 event in the next summit, so I might grind that next, and also I need better dragster parts as there always seems to be a speed trap. Most events in the next summit are with loaned vehicles. The one that isn't needs a 300ZX Malu edition which can be obtained via TC2, but I started the story you have to do to get it, and good grief it's so tedious, I'll just buy it in TCM instead.