that gauge reads in bar matey same as my blitz one. it will have the inlet manifold take off, but i dunno about the hollow bit at the top.. on my one, theres a threaded bolt, with a nut and grub screw... you wind that in or out and lock the nut on it, and it adjusts the bov volume. im guessing its to tighten the spring up inside.so you get a softer quieter noise or a sharper, louder pitched noise.. check its not got a thread inside mate, as i personally havent ever owned a hks bov.. just an idea mate