Last year I changed from an Edelbrock to a Holley and lost a vacuum port. I left the pcv disconnected and remember thinking I will let it breathe on it's own until I could get a breather filter. I was 15 miles down the road when the light bulb in my head went on and I remembered the pcv won't open without vacuum and I'm building pressure. I pulled into the closest parts store, opened the hood, and found my water pump covered in oil and little puddles of oil on top of it. My intake gasket blew out from the pressure. I bought a nice K&N breather which slowed the leak, which I soon fixed, but it never ran the same. I reconnected the pcv a couple weeks later and it ran like it always used to. Therefore, I recommend a pcv valve.