[diesel_john]

the impeller would be gasoline proof, the bearing material would be what?
lets define the pressure to be 7 psi.
on the ball in a track design, an aluminum ball would be good, but all kinds of glass beads are available now. think glass would be to heavy? know any arts and crafters, a 6mm black glass bead would be good.
let's estimate the flow per min. @60 MPG @60 MPH would 1 gal,/ hr. or about 2 oz./ min.
@30MPG would 4 oz./min.
so 2 to 4 oz/ min would be a range to test over.