If you have a catted exhaust I would say yes, there is harm that can be done.
I shot flames out all the time when I tried the HKS bov for a week, but luckily I am catless. If not, I probably would've been shooting flaming chunks of catalytic converter :lol:
well i believe the shoot flames part lol cause that happens to me all the time lol!, i have a cat back and also intake and hks bov and the sound of the exhaust and bov are great and so with that i have a slight draw back that my car is running rich and that i shoot flames . . . i can live with that . . .