Not necessary, but highly recommended. Without it and 8 discs is safe. But 12 discs and with it is much better. It kind of run flat without it... but you got the noise... Look out Indysuperbike website... they were quite cheap $265.00 or something like that...Get the blockoff plates while you're at it, just another $40.00I thought that they Supertrapp looked awesome. Are you saying that we should get the PCV also? That would add to the cost of the whole thing. But I would be interested in that definitely.