Our rides are all about science, especially physics of the thermodynamic kind. Almost every aspect of performance involves some form of heat generation and the control of that heat. Survey a hundred people and they would tell you the top producer of automotive BTUs would be the engine, followed by the transmission. After that, people would wander into lesser-contemplated areas like the brakes and differential, while the truly deep thinkers would list the air conditioning system. Somewhere on that list would fall the power steering system. Now for those that cruise around town or even blast down the local drag strip, the heat generated by a car's power-steering system is nearly inconsequential. But to those that gravitate between going left and right in quick fashion, it's of paramount importance.
The job of the power steering pump is to move fluid under pressure. When pressurized, it helps move the parts inside the steering rack, or box, thus lessening the amount of energy the driver has to expend to turn the wheel. But, like all things in life, there's a trade off, namely, heat. The mechanics of pumping creates heat, which can build up in the fluid causing all sorts of nasty happenings, but the net result is a loss of steering.
Our '01 project, Black Betty, has been suffering from power steering woes. Around town it was ok, but once on the race track, the system quickly went to hell. Worse than the boiling fluid was the loss of steering assistance, which is never fun in the middle of a turn. To fix our fluid-based dilemma we went to Jeff Roethlisberger of Turn One. Having spent 16 years as an engineer at Saginaw Gear, GM's steering division, he knows steering. Add in his current gig of supplying steering gears to Nextel Cup and other race cars, and one would have to move him into the expert category. If that's not enough, Jeff's father was the Chief Engineer of steering at Saginaw. Guess it's safe to say they have hydraulic fluid in their blood.
What Turn One specifically does to the pumps is a closely guarded secret. But, according to Jeff, "We lower the amount of volume that the pump puts out per revolution. The factory pump and Turn One's pump are vein-style pumps. The factory pump puts out x cc's per revolution of the drive shaft. Turn One modifies the internal components to reduce that output." Less output equals less heat and happier fluid. LS1-powered fourth-gens are known for eating pumps and offered optional oil-to-water coolers. These worked well for mild track use, but it was really only treating the symptom and not the root cause. The factory tends to over boost (pump too much fluid) because it helps give that easy-to-turn feeling during low-speed maneuvers, like parking at the grocery store.
Back in the day it became almost absurd. Remember that old car with the steering wheel you could spin with your pinky? Sure, granny loved it, but it generated a ton of heat and even cost a few horsepower. Worse was the vague, disconnected, feel these cars had on the highway. Nowadays, car manufacturers pay more attention to steering feedback and effort, but they still err on the side of making sure effort is minimal for low-speed (ie, low rpm) maneuvers. The Turn One pump lowers the volume to more of a happy medium between low-speed effort and performance-driving longevity.
Pumping It Up
•The below graph represents pump flow (y axis) vs. pump rpm (x axis) of a stock production pump and one modified by Turn One.
Analyzing the solid-line graph of the stock pump at approximately 900 rpm, the pump achieves flow control mode, which means the pump will deliver one constant flow to the steering box/rack at any rpm above 900. The 2.6 gpm flow-control value is used here as an example, but the actual flow control may vary, depending on application.
Following the dashed line of the stock pump at 5000 rpm, the pump delivery is 15 gpm. This is the total volume at 5000 rpm, with 2.6 gpm being delivered to the box/rack. The other 12.4 gpm is being re-circulated internal of the pump. This excess flow is what creates high fluid temperatures and robs horsepower.
Analyzing the Turn One pump graph, it achieves 2.6 gpm flow control at 1300 rpm. At 5000 rpm it's pumping a total of 10 gpm, re-circulating only 7.4 gpm. That's 5 gpm less, resulting in lower fluid temperatures and less parasitic horsepower consumption.
You may ask why the production pump is designed this way. The reason is to have more than adequate flow at low engine rpm. So due to production variation, higher than average steering effort wouldn't be experienced during low-speed maneuvers.