By Archie Bosman–
Using the correct flow valve: Electric steering in mass-produced road cars is now widespread. It is a little like ethanol in our fuel: you’ll be hard pressed to find an enthusiast who favors it yet we are stuck with it.
But actually we aren’t. Hydraulic power steering systems that provide superior feel are still readily available to the racer. However, it is not widely known that steering pumps can be tuned for more feel or alternatively for more assistance.
Optimizing feel to the racer’s steering is a bewildering task for most of us. But KRC Power Steering accomplished it by introducing a range of replaceable flow control valves for their hydraulic steering pumps.
The flow control valves, nine in number, perform a function similar to that of jets in a carburetor. In varying their flow from 4 to 12 liters per minute, approximately one to three gallons, the largest orifice provides maximum steering assistance while the smallest provides maximum steering feel.
Though the standard KRC pump flows 8 liters per minute, by using flow control valves with larger orifices, those marked B, C, D, or E, the flow rate can be increased to 12 liters per minute (3.17gals) in one-liter increments. The higher letter indicates greater hydraulic assistance, although less feel. In contrast, flow valves marked with numbers 4, 5, 6, and 7 provide less assistance; the lower the number, the greater the feel but the less assistance.
Momentary loss of power or “pump catch”
So how do you achieve optimum steering feel? According to KRC’s Ken Roper you reduce the size of flow valve orifice until you experience pump catch. Characterized by a momentary loss of hydraulic assistance, pump catch can be induced by steering the vehicle in one direction then swiftly changing to the other direction—as oval track and road racers do. The quick change of direction increases the pump flow requirements and the momentary deficiency is caused by a sudden lack of flow of hydraulic fluid. When pump catch is encountered you can increase the orifice by one or two sizes, which will eliminate it and cultivate a better feel. As a result, the steering will be accurate, responsive, and without any tight spots. Invariably, it inspires confidence and hopefully rekindles some lost magic to the driver!
“But from an engineering perspective it was such a tricky thing to get right,” says designer, Ken Roper. “The critical orifice is created in the -6 flow control valves and each valve is drilled undersize and then brought to the exact size by reaming. The difference in diameter between each orifice is a mere two-tenths of one millimeter (0.007in) and each orifice is held to a tolerance of 0.0002in.” Without maintaining these strict tolerances the technology won’t work. In fact, it was when KRC first experimented with tighter tolerances throughout the pump’s design that they discovered its fuller potential.
To the best of Roper’s knowledge the KRC pump is the only one that can be tuned for steering feel. “For years, most of our competitors have just modified OEM production power steering pumps.” But OEM pumps, by necessity, have relaxed tolerances to accommodate mass production and cost requirements. In contrast, KRC’s Flow Control Technology uses exacting tolerances that are impractical in the OEM environment. “Although several of our competitors have tried over the past 16 years to duplicate this process,” adds Roper, “it cannot be duplicated in mass-produced OEM pumps—that’s the difference between a $200 production pump and a $600 proper racing unit. Wide tolerances cause excessive internal leakage that makes it impossible to regulate the output flow of the OEM-style pump.”
The orifice of each flow control valve differs by a mere two-tenths of one millimeter (0.007in) yet each one alters the flow rate by one liter per minute!
KRC Power Steering