As you race through night and gather heat and rep, you'll have access to the high heat races. Once you reach rep level 47, you'll have all of the elite parts unlocked. Once all of the elite parts are unlocked any high heat race you do will yield you with ultimate parts. If you do both High Heat 3 and High Heat 5, you'll unlock Ultimate+ parts.
Once you've unlocked all parts, I bought a Huracan Performante and applied all of the Ultimate+ parts in the Engine section. The rest were Elite. Straight away I had over 400 performance.
I did any race and this popped as soon as I crossed the line.