KRC Power Steering pump with a Hydroboost.........

[stevant]

So, I have spoken to a few forum members and bounced this question off them. I've always respected their opinions and insight. Long distance friends now you might say. I have a question for those running a KRC power steering pump with a Hydroboost. Are there any out there? The stock flow valve on a KRC pump is 2.22 GPM which makes the Hydroboost for my brakes very happy, and they feel great. Unfortunately it's too much flow for my Mustang steering rack. Steering is way too sensitive. (I know + Castor is an option) The great thing about the KRC pump is that there are 9 available replacement flow valves which can alter the feel of your steering. Super easy to firm. Easy to install and no extra plumbing needed. With that being said, according to KRC the mustang rack works well with the replacement valve ID:6 which is 1.7 GPM. They are smaller steering racks not needing as much flow. Some guys like it at ID:4 which is 1.18 GPM. The problem here is that making the steering firmer is what I'm looking for but unfortunately it will have an affect now on my Hydroboost brakes that like 2.0 GPM. Hydrabrake and KRC both feel that the 1.7 GPM will be fine for the Hydroboost but what about 1.18 GPM? I'm hearing that's a nice feel for the Cobra with the mustang rack. How will it affect my brakes?

Does anyone run a KRC PS pump with a Hydroboost?…… and if you do have you changed the flow valve to restrict the volume to stiffen up the steering?...… how are the brakes, do you feel a difference in them now?

I'm hoping someone has a similar setup and has tried a new flow valve. I'm going to start with the ID:6 valve and see how that affects my brakes. I want to try the ID:4 but once again is that not enough GPM for my Hydroboost and what problems can occur if not enough GPM flowing through?

[rich grsc]

You do realize the hydroboost was designed to work with the Ford pump, and the Ford steering rack. Setting the KRC pump close to the Ford specs, the brakes will still be fine. Both work on pressure, not flow.

[stevant]

I was told by Hydrabrake that the Hydroboost works on flow. Flow “is” pressure. I was also told by KRC that their pump is based on flow and by reducing or increasing flow using the flow valve (GPM) that’s what controls the feel. Now I’m confused. Hydroboost and KRC refer to the volume flow “Is” pressure in regards to how their units operate. The KRC flow valves do exactly that, control flow as they reference the flow using GPM. I’m going to run the ID:6, 1.7 GPM, which is what the ford rack usually runs as per KRC. Not debating what actually controls it, pressure or flow, as in they are one in the same?

I’m just repeating what was explained to me from KRC:

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.

Here is Hydrabrake info:

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.

So i should not have a problem with the reduced flow it sounds like, just a stiffer wheel and brakes that should still work fine......... right?

[edwardb]

Possible to way overthink this IMO. I'll repeat a little what we've talked about already. Just a little more since it's not with thumbs on my phone... Maybe will get some reaction or thoughts from others. I've used the KRC setup twice. Both without hydroboost, but still maybe of some value. Based on recommendations from another builder that ran the KRC system, I've immediately changed both to the smallest 1.18 GPM (ID Mark 4) 253040000 flow valve. The boost is still quite a bit, and for our lightweight cars, the effort is still moderately light at speed. Some might say too light. But with the proper front end alignment (+8 degrees caster, -0.5 degrees camber, approx 1/16 toe in) drives perfectly IMO. In both cases with a Breeze 3-turn Unisteer rack. Which is basically a Mustang rack. IMO, recommending the ID:6 1.7 GPM flow valve for a Mustang rack is probably a good recommendation for an actual Mustang. But still may be too much for our cars. Now add the hydroboost to the discussion, which admittedly I don't have experience with that exact combination. What do you think the hydroboost is going to do with the lower flow rate valves? Stop working? No, I expect it will still provide power boost. Just maybe not quite as much. Will it be like the heavier pedal of manual unboosted brakes? No. Which BTW the Wilwood setup is designed for.

Note also for reference, while also not 100% applicable, my #7750 build had power steering and hydroboost brakes. But it used the Fast Freddie electric pump setup. So not engine powered and obviously not KRC. On my first drives with that build, I felt the PS was quite overboosted. The Denso electric pump used in that setup had an adjustable valve that you could turn to control the boost. I turned it down to get the PS feel where I wanted it. I never felt like it adversely affected the hydroboost operation. The brakes in that car were clearly boosted and worked fine. That was a Wilwood pedal box, with the bigger Wilwood 6-piston fronts and smaller single piston rears. The Wilwood upgrade Factory Five offered (and I think still do) for solid axle cars.

My suggestion? They're easy to change. You already know how the standard one works. Try the two lower rates. Put in the ID:6 1.7 GPM flow valve. Drive it. Brake it. Then switch to the ID:4 1.18 GPM flow and do the same. Keep the one that gives the steering and brakes you're happy with. You'll always have brakes so it's not a dangerous test. Your brakes will work with no boost.

[stevant]

Thanks Paul, you always have additional information to share. I think this is great info to share with the forum. I won’t be the last to use this setup, I’m sure this info will help others who want to also. Wi keep you posted if my progress.

[Hacksaw84]

Thanks Paul, you always have additional information to share. I think this is great info to share with the forum. I won’t be the last to use this setup, I’m sure this info will help others who want to also. Wi keep you posted if my progress.

Did you test this? If so what did you decide?

Michael