Moved to ”Racing, Rally & Autocross”...
What type of racing??
Carrera26 has a good suggestion though.
While not all sanctioning bodies or event venues will require a Snell rated helmet,
if you get one, you're pretty much covered everywhere.
BTW, if you do plan on any Road Course type events, they will more than likely require a Snell "SA" (Severe Application) rating.
Autocrossing, I.E. SCCA Solo2 type events require just the Snell "M" (Motorcyle) rating.