pressure to the calipers, but small bore masters won't put out the volume TVolve needed to fill caliper pistons, and vacuum pumps won't keep up. You can also spend a lot of money on great big calipers, but they tend to be more demanding of volume and pressure, so they don't work unless you have a Hydro-Boost. It provides great valve cover clearance, and exhaust pipe clearance when frame mounted. The Hydro-Boost fits any where a vacuum booster does. It can use stainless braided hoses or crimped high pressure rubber type. We have many direct replacements, our own retrofit applications, and can design anything else. http://drozforskolin.org/tvolve-reviews/