[mr0077]

Tim, you're right, the manifold vacuum (actually air flow) lifts the sliding valve up, but actually it moves up to the seat rather than up off the seat...at lower vacuum (under engine load conditions), the weight of the slider allows it to drop away from the seat and allows more air flow at lower vacuum (sounds backwards), up to the max flow permitted by the orifice in the PCV valve. I had the parts guy look up the application for a high performance 427 Ford (Mustang, I think) and bought that one, figured it would have flow characteristics close to what I needed...but is there any real difference? I dunno...