You’re going to find it tough since vray might see that as noise - if it’s for moving footage it’s going to be a problem, for stills just turn your quality down and use a tiny noise map!
set flakes eeee size if I’m not wrong to something like 0.0001(I’m using 3ds max btw). And then fixed or adaptive DMC set to like 6/10 min/max/ treshold to like 0.0001 and Enjoyyyyyyyyyyy. Will take quite long time, and u need multiple flake max to reproduce proper car flakes.