this sounds suspiciously like the old "380 brake by just using tesco 99 fuel" saga to me

if you read the post a few years back when this was claimed from an M3 they sort of hide the fact that it was a csl, so that made it only 20 brake to find in the first place, then they dind't tell you it'd had an exhaust fitted, or that it had been remapped, just the "it's made 380 brake simply by inserted tesco 99 ron fuel into the tank and wahey!"

so if this has made around 20 brake ontop of what it was supposed to make with the afrementioned mods, i don't see why it's nor plauseab;e or feesable to see those sorts of gains on a good base car