Quote Originally Posted by EM1toEVO
Stick with the stock Evo IX metal bov. It is fine up to 25psi. Anything beyond that, you might need to get a stronger one. I like the aftermarket bov's too, but don't get one just for the sound. Waste of money IMHO.
you can do what is call the "Gus" mod to the valve and have it hold better

http://forums.evolutionm.net/showthread.php?t=260029