@RPM Bibblefish - I tried to rebuild that Miata but for some reason can't upgrade the supercharger once I've added it (I've definitely installed the supercharger you listed). There seems to be no option to upgrade it to race unless I'm missing something
Also - I couldn't get the springs to the exact values you've listed either, so just went as close as I could. And since I couldn't upgrade the supercharger, I had a lot more points left to spend so added the sport transmission plus a lot of other engine upgrades. The car still felt almost identical to your build/tune although I managed to get under 8:15 on my first lap - however, the car has a lower top speed despite me making it able to get into 5th gear more often. I guess because I'm missing the race supercharger.