Traditional hydraulic power steering systems are powered by a belt-driven hydraulic pump. My 1989 Ford Van uses a Saginaw "canned-ham" power steering pump, as do most GM cars and trucks of similar age. Fords typically used their own pump setup but put Sag's in the vans. These pump typically run 2.0-4.5 gpm and 700-2,400 psi.
Borgeson’s pressure-adjusting kit (part number 899001) includes a clamping tool, six shims, and installation instructions for lowering the bypass pressure on all GM self-contained and Type II power steering pumps.
Here's a little chart showing how it works.
These kits are used most commonly by hot rod drivers looking for more steering "feel" on the race track. I'm interested in using one for the same reason (not on the racetrack though, just tired of my numb steering feel and think reducing the over-corrections it causes waste fuel) and think maybe reducing the pump's output can reduce the hp-loss of the belt drive. At the lowest normal rates (2.0 gpm and 700 psi) the pump has an input requirement of .82 horsepower. This is well below the stock settings of my van. It's closer to 1.93 horsepower. I may not be able to tolerate the pump running at its lowest possible setting but if I could, I think 1.1hp for ~$20 is a pretty good deal and might even be directly noticeable in mpg. Thoughts?