Overboosted steering with hydroboost setup

[dontlifttoshift]

Educate us. I am open to hear why bleeding off pressure into the return line is a better solution than fixing the problem at the source by changing the size of the orifice and limiting the volume of fluid that can flow. Especially considering that it is more costly and more complicated to do so with the Heidts valve.

Here is an article from KRC about changing power steering feel, not a single mention of pressure in the whole thing. http://mooregoodink.com/in-all-proba...eering-feel-2/

Use right flow valve get better steering feel
by moore1 | Mar 5, 2014 | Press Releases | 1 comment

By Archie Bosman

KRC-FlowControlValvesKennesaw, GA: 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 it has been accomplished by introducing a range of replaceable flow control valves to the hydraulic steering pump.

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.

How it works

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”

01 (2049)Lrcu
By changing the orifice in this blue fitting you alter the feel and weight of the steering. The larger orifice provides maximum steering assistance while the smaller provides maximum steering feel. If it’s too heavy, increase the orifice diameter; if too light reduce it.

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.

02 (0366)Lr
KRC’s Pro Series hydraulic power steering pump is a magnificent accomplishment. But you’ll only appreciate the true scale of its merits when you realize it can be tuned—more feel or more assistance or some setting in between that suits your driving style.

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.”

ValveSizes
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 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 but greater feel.

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!



Source
KRC Power Steering
Kennesaw, Georgia
(770) 422-5135
www.krcpower.com

Some more light reading from Turn One. I linked the Pressure vs Flow article earlier in the thread. https://www.turnone-steering.com/blo...him-kit-theory

DEBUNKING THE SHIM KIT THEORY
Ever have light steering effort or twitchy steering? At some point or another, you probably have. It seems that somewhere along the line, a rumor started that the fix to this dilemma is to use a shim kit on the pressure relief valve to lower pressure in the power steering pump. Unfortunately, this is a myth.

Many believe that when a steering system feels over assisted the system has too much pressure and the fix is to install a shim kit. Installing a shim kit will reduce the pump's pressure capacity. However, if the pump's pressure capacity is set below the demand of the steering unit control valve, then the system will not operate properly. Installing a shim kit will require you to reduce the pump's pressure capacity so low in order to get the desired feel at high speed. This would result in giving you no assist under low speed maneuvering because the steering unit control valve demands more pressure. Running the pump under these conditions will dramatically shorten the life of the pump.

In actuality, if your system feels over assisted, it has too much flow. The control valve in the steering rack or box is sensitive to flow rate (GPM). When the control valve receives more flow rate than what it is designed for, it gets overly sensitive. This results in a system that responds too quickly and gives a light or over-assisted feel. The control valve in the steering rack or box essentially communicates to the pump how much pressure to provide the system. As outlined in our "Pressure vs. Flow" article, it is adjustments to the flow that improve your steering feel.

The proper way to gain steering feel is to use a properly sized Turn One flow restrictor. Not only is this an easier adjustment, but it will have no adverse side effects to the life of the pump. A properly sized flow restrictor will make the pump compatible with the steering unit control valve requirements. This will give the driver the desired steering feel without compromising the steering system.

[Hydratech®]

For those that may not know, I am the founder / owner / master engineer of Hydratech Braking Systems (high performance high end hydraulic brake assist systems aka hydroboost). I have 35 years of experience in building extreme performance vehicles, including modifying and tuning power steering systems on thousands of different build types and applications. I have been a member here at Pro-Touring.com since Larry started the forum, and used to post extensively years ago. These days I am so busy with Hydratech that I hardly have time to even lurk through forums anymore. The reason why I chimed in on this one was because I spotted a discussion that we deal with everyday professionally - the occasional disparate needs of a hydroboost unit versus the needs of a steering gear. My opinion on this entire thread is that everything being discussed IS accurate, however nobody ever wants to touch upon the "voodoo" of "no load signal pressure" as I refer to it. Sooo… Here we go...

Everybody can wrap their mind around PS system max relief pressure - it occurs in every vehicle when you crank the steering wheel all the way full right / left against a steering lock. You hear the pump hiss and growl while it is under its maximum load scenario. That is max pressure relief, where adding and subtracting shims to the pressure control valve comes into play. Max pressure relief dictates essentially how much horsepower is going to be put up against a power steering system load. I don't have dyno readings to back this up, but for the sake of discussion, my estimates are that a pump set at 800 PSI max pressure relief will take about 6-8 crankshaft horsepower at full load. When you crank your steering wheel all the way against a steering stop, placing your PS pump at max load, you can hear the engine strain against the load, typically dropping the RPM anywhere from 50-100 until you let off of the steering wheel. Once you let go of the steering wheel, the load is removed and the pump then relaxes, the RPM's go back to the usual idle speed, right? Note that an EFI car will drop less RPM's because the idle air control system is performing a load compensation to maintain a target idle speed setting. Ok, now raise the max pressure relief setting to 1200 PSI. My observations are that you are now moving to about 8-10 horsepower at full pump load. This will now typically drop the engine RPM 90-125 under full pump load. Move that max pressure relief setting to 1500 PSI, and I estimate that you are now in the area of 10-12 horsepower of load at full max pressure relief, dropping the engine RPM's up to 150-175 under max PS pump load.

The physics of hydraulic fluid power transmission is literally taking these amounts of crankshaft horsepower in my estimates above and applying that power to a hydraulically driven device, such as a hydroboost unit or a steering gear. In the real time sense of the scenario, this literally equates to how much horsepower / torque is being transmitted to the driven device. So, let's look at the hydroboost unit and steering gear in this discussion. The gentleman states that he likes his braking actions, but doesn't like his over assisted steering actions. To my sense of the scenario, the appropriate amount of "hydraulic horsepower" is being applied to the brake assist unit, resulting in crisp, powerful, responsive braking actions. Now downstream of the hydroboost unit is the steering gear, which is receiving more power than the driver wants. Reducing or detuning the PS pump power output is going to affect ALL of the "driven devices" operations (both braking and steering). The PS pump output fitting was swapped out with one that has a smaller orifice or jet size, resulting in a lower GPM (gallons per minute). This reduction in flow provided positive results for this scenario, as it suited the driver's particular tastes in the reduction of power to the steering gear. While the driver may not have particularly noticed, as he was more focused upon the steering actions, the hydroboost unit was also detuned. The model of hydroboost unit he is running is a powerful unit, so it is comparable to shaving 75 horsepower off of an 800 horse engine - you're not going to notice that very evidently until you make a pass commanding full power. Since the hydroboost unit is such a powerful item, the driver did not particularly sense that some power has been reduced as there is so much available in reserve. As an interesting side note in the discussion, the hydroboost units are also a nonlinear / variable output device. This means that the brake assist unit can compensate for a wide range of pressure available to it without the driver sensing much of a difference.

With all of the above being said, the driver essentially has five basic choices:

1) Detune the PS pump GPM further still with an even smaller jet / orifice size
2) Replace the steering gear with one that has a stiffer torsion bar (the input shaft) to increase steering effort
3) Blow off the volumes / pressures available to only the steering gear (the Heidts PS101 valve)
4) Increase the caster which will require more effort to steer from center
5) Live happy with the improvements already registered

Now, let's get into the PS system "voodoo" that never seems to be mentioned. Look at torque versus horsepower, or voltage versus amperage. You can't have one without the other. The same essentially goes for volume versus pressure. To really get a proper feel for what is going on in a PS system, a gauge needs to be installed into the line coming out of the pump. Increasing the PS pump orifice size increases the GPM, while decreasing the PS pump orifice size reduces the GPM. Most can wrap their head around a carburetor jet change - the larger jet flows more fuel and the smaller jet flows less fuel. Now here is where it gets interesting in a PS system. Everybody is aware of PS pump max pressure relief PSI settings, but most don't know that a PS system sits at a vastly lower pressure when no load is commanded, such as just sitting there idling in park, or just rolling down the road. This varies from vehicle to vehicle, but let's say that most OEM passenger cars will be at about 100-150 PSI of "no load signal pressure" as I call it. Very little actual (crankshaft) power is being hydraulically transmitted through the PS lines / system overall because the driver is not commanding a load (such as steering or braking in this hydroboost equipped vehicle). This results in good fuel economy, and more importantly no particular heat buildup in the PS system besides basic under hood operating temperature. There is just enough pressure to operate the driven device(s) in a standby mode (the hydroboost unit and steering gear in this discussion). Now here is where it starts to get into areas that most never hear of. There are actually two pressures that need to be discussed - max pressure relief and no-load pressures.

Everybody these days is starting to hear more and more about flow – things that weren’t particularly discussed much many years ago. This scenario now has people acknowledging that tuning the PS pump flow is an important move in tailoring steering feel. But just what is flow? And why does it impact steering feel? Well, here it is: FLOW *IS* PRESSURE. If you have a gauge hooked up to your PS pump, you will find that lowering the flow in the PS system lowers the pressure. Increasing the flow increases the pressure. That myth about altering max pressure relief settings by adding and subtracting shims to attempt to change steering feel IS bogus, but it was however close to getting to the real point, which is the general system pressures CONTROLLED BY FLOW. A flow of 2.0 GPM +/- typically results in a gauge reading of 100-150 PSI depending upon the steering gear design. By contrast, a change of flow on the same car to 3.5 GPM +/- can jump that gauge reading up to 275-350 PSI. So now you clearly see that flow is pressure, and pressure is power. Now you can see why too much pressure (as a result of too much flow) results in overly assisted steering in most cases.

Further to this, different steering gear designs have varying throughputs. A typical muscle car steering gear compared to a 1+ ton truck gear will have a different flow throughput. A 3.5 GPM flow rate on a truck steering gear will not result in as high of a “no load pressure” as compared to a 3.5 GPM rate on a passenger car box. Rack and pinion steering gears also vary considerably in their flow throughputs. Many aftermarket rack conversions are using Ford spec gears. GM spec racks are designed for higher operating pressures, while the Ford versions are designed for lower operating pressures. The latest "classic style" integral steering gear designs (such as the highly popular Jeep box) are using rack and pinion style pressure control valving to provide improved steering feel. You can have a high pressure applied to a steering gear yet still have a firm feel if that particular steering gear is equipped with a stiff input shaft (aka torsion bar), but that’s getting off topic into a different discussion.

One more point I'd like to make is that we are seeing everything from soup to nuts on PS pumps these days with our customers. The best results are always actually on a dead stock pump! The aftermarket / replacement pumps we are seeing are being equipped with large orifices, flowing way too much. I suspect that this is in an effort to prevent a customer from experiencing "pump catch" during high action steering maneuvers, or possibly to compensate for a heavily worn steering gear, though it usually brings on noise / aeration / and burnt up pump issues. When you buy a pump, please investigate what the listed flow rate and max pressure relief is said to be at. We coach customers daily that 2.2-2.6 GPM and 1350-1450 PSI max pressure relief is our general target. A day doesn't go by here where we have a customer come back with a drill bit test showing up to 13/64th's ! That's .203" which is insane, considering we look at 9/64th's (.140") as our max acceptable sizing.

The suggestion of using the Heidts PS101 valve between the hydroboost unit and the steering gear is to allow a variable knob adjustment of how much flow can be blown off before it reaches the steering gear. So, since flow is pressure, dumping off some of it into the return line circuit effectively lowers the pressure available at the steering gear inlet port as measured with a gauge at that point. The lower pressure entering into the steering gear increases the driver effort to steer the vehicle, resulting in what most are looking for – that firmer feel. Now kill too much flow though and you will then surprisingly induce slop into the steering. Why? How? Take your average car and you will see that you can move the steering wheel back and forth 1 inch +/- when the engine is off without the tires actually responding. That is because there is no pressure going to the steering gear and you are only flexing the torsion bar (steering gear input shaft and valving).

Summary? FLOW IS PRESSURE!



Yes, I got tired of typing, but its going to be a good start on a new tech article for the all new website that is currently in the works...

[Hydratech®]

http://www.classicperform.com/tech_a...PropValve1.pdf

[Barrrf]

I love this thread. I had the GM truck power steering pump and astrovan hydrobooster and Jeep Steering box in my car all last summer. 3 pumps and 2 reducing valves later and I couldnt get the pump to not whine. I determined that the best course of action here would be to switch over to the type 2 pump which apparently flows right where its supposed to. Im in the middle of installing that stuff currently.

Thanks for your contribution Paul! I appreciate the read!

[Hellrace]

My 70 Camaro wich has a LSA engine I'm currently upgrading with power steering and hydrobooster, and I have bought the valve from heidt's to solve the pressure going to the rack and pinion steering I have. So its nice to see what Paul is saying, it going to work absolutely perfect I guess
Here are the instructions the comes with the valve:
https://www.heidts.com/inst/in-064.pdf

[cactuss4]

I love the information!!

Keep it coming, typically there are multiple ways to arrive at the same destination. Having real technical info provided really helps. Heck, this is not usually our first nor our last build, so learning to help the next build or hell change of our current rides is always helpful.

Thanks everyone!