I recently found these C3 power steering flow rates from Jim Shea, in one of his papers.
He is well respected on this forum and was a GM engineer for the Saginaw power steering group.
So if anyone knows these systems well, it is him.

He says these are the stock OEM flow rates on various C3s.
Apparently they changed over the years
I have driven a dozen different C3s, and some feel fairly firm, and some feel extremely light.

Year OEM Flow Rate
70-73 = 1.6gpm
74-81= 2.9gpm
82 = 1.9gpm

He also had orifice sizes:
orifice Flow Rate
.144" = 3gpm
.130" = 2.5gpm
.1144" = 2gpm

So if anyone wants to change how their power steering effort "feels", this is a good range to try.

This flow restriction orifice is located in the back of the pump, and gets accidentally swapped out when you get a new or rebuilt pump.

 

This is some other "tuning" information I found from several manufacturers:
That complete thread discussion is here: "Modifying my Borgeson Box" link


HOW TO TUNE A POWER STEEERING SYSTEM

I have heard from a couple of guys on how to tune the "feel" of the Borgeson. The normal being "too light"

Some of you guys are running Type 1 pumps, some Type 2, some a Hydraboost, and some a rack-n-pinion. so there are many variables.

Here are some remarks from the Pro-Touring Forum, from the head engineer for Hydraboost, regarding a power steering that is too "light" but the Hydraboost brakes are fine. 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 with it

Unfortunately in a hydraboost brake situation several of those choices also affect the brakes. 2,3 & 4 do not and only affect the steering.

He also mentioned: "We coach customers daily that 2.2-2.6 GPM and 1350-1450 PSI max pressure relief is our general target."
(These are basically OEM specs). And many aftermarket parts have way too much flow.

(Author edit: However a stock Corvette has the maximum pressure set at 850 to 900psi, to keep from rupturing the many moving hoses in the system).

"A flow of 2.0 GPM +/- typically results in a no-load gauge reading of 100-150 PSI depending upon the steering gear design."
This is where the psi remains for 98% of the time. And when you change the flow restriction larger for more flow, this no-load pressure also increases, giving you more assist/more power/less feel. If the no-load psi is too high, you will also have over-heating problems. Max pressure usually only occurs when you hold the system against it's stops. This "no-load" pressure is far more important the rest of the time.

To tune the flow restriction here is a procedure: (like if you have too light of a feel)
KRC Power Steering says:
Too much flow results in overly-sensitive steering feel.
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.

 

A very well written post there leigh1322! Thank you for the information!

This is very similar to what I ran into with my Steeroids system after installing it. I tried several pumps and each acted differently. I eventually found my way to the guys at Turn One performance power Steering and they helped me understand what was going on in my system. It was all about the flow rate that would make the Steeroids a great system after it was setup properly.

With the wrong flow rates the system would squeal and make all sorts of noises as it tried to move the wheels. After getting the flow rate where it needed to be the system would operate like any newer car with power rack and pinion in it. My C4 came with a power rack and pinion and it is a great steering system, very precise and tight. This is what I was striving for in my C3 as the old power steering system was less than desirable with it's dead spots and looseness. I rebuilt the steering systems up front and had a good starting point. First I rebuilt the factory steering system, then I drove the car for a few years and finally made the decision to go with the power rack and pinion system.

Now I am looking at a Volvo Power Steering pump that is electric and this might be the best option of all. I would LOVE to remove the power steering pump and replace it with a smaller electric pump, no more hoses near the headers. Has anybody done an electric power steering system on their C3 yet?

 

I think @MotorHead and @DblTrbl have done this. Perhaps they chime in.

https://www.corvetteforum.com/forums...-steering.html

 

Interesting info. I had no idea there was such a variation. I wonder if this is at all related to some having a higher PS hose failure rate than some others. Until recently with a custom return hose, 4vettes was going through them constantly while other are on the same hose for years on end. Does pressure increase with volume?

 

The PS system only runs normally at 100-150 psi.
Even when turning.
It only goes higher than that on very quick aggressive autocross style turns, or bottoming out the wheel, and holding it against the steering stops.
The 800 psi relief spring is just there to keep from popping the hoses, when someone does that.

100-150 psi is enough assist during normal steering.
But if you double the flow at idle, it doubles the psi, and then it could be 200-300psi all the time. Even while cruising.
That would stress the hoses much more, and could easily lead to overheating and foaming over.

Also if someone has replaced the PS pump, and it has a normal chevy 1200psi relief spring, instead of the C3 800psi one, that could definately make the hoses leak.
It should not really ever go that high while driving, but it will if you hold it against the steering stops.

 

isn't the return hose on the low-pressure side, i.e. no pressure, just return to the reservoir or through the cooler?

maybe they're using hose that's not rated for power steering fluid?

 

Yes the return hose should have zero pressure, it's just a dump into the pump / reservoir.

The PS control valve offers the primary system restriction when centered, that is what causes the constant 100psi in the hoses.
So the system psi of 100-150 is controlled by the flow rate. And two different size restrictions, one in the pump, and one in the control valve.

When cruising equal flow goes thru both sides of the ram. When the wheel is turned, the control valve shuts off one side of flow to the ram, so the 150psi only acts on one side of the ram, adding assist to the wheel. Closing or partially closing half of the control valve restriction causes the system psi to rise.

The psi would continue to rise except that the ram moves and relieves the psi back down to 150.
When the ram hits it's stop, the greatly restricted flow caused by half the control valve closed, causes the psi to spike drastically, until the pump relief valve opens at 800psi.

The control valve is not just an on & off device. It very smoothly & incrementally adds more assist, almost as if it were two needle valves. Smooth steering movements do not use much assist. Full assist would require a sudden large jerk of the wheel to completely close half of the control valve.

Decreasing the pump flow rate, with the same control valve restriction, lowers the system psi to 100 psi, and gives a lot less assist while turning, firming up the steering wheel feel. IE: one finger steering vs two or three finger pressure.

 

for my 78 equipped with the Borgeson conversion, i'm settling towards a 0.109" dia drilled orifice. I had been using a drilled 0.092" but that wasn't enough assist, but still way smaller than the original 0.116" orifice. I bought some Turn One flow restrictors, the smallest one, 0.089", and use that as the starting point.

ETA: next time i'm "in the area" of the back-side of the PS pump, I'm inclined to try "one size smaller" on the drilled orifice flow restrictor, just food for thought. maybe a #38 drill bit (0.1015"), or a #39 drill bit (0.0995").

 

That sounds like a great plan!

 

Glad I found this thread to see that I'm not the only one with these issues! Bought a '79 C3 a year ago and have been going through all the different systems. The power steering system is the factory installed system. I rebuilt all the power steering components and installed a rebuilt PS pump and all new lines. Drove it for 15 minutes and the pressure line from the pump blew out. The steering was extremely over-sensitive. Afterwards I found some info on this forum about installing the Borgenson 899001 pressure reducing kit and Speedway motors flow reducing fitting. Went ahead and started with all the shims to get max reduction of pressure. This time the steering feel was much better- much less sensitive, but it still seems to be overheating the fluid and I think I've blown another line as it's leaked a bunch of fluid and the steering started getting jerky and wonky as I was trying to get home. Just like last time it actually melted the power steering fluid level dipstick as it's getting so hot! Other than too much pressure output from the pump, anything else that could cause things to heat up so much? I can't figure it out. Worked great for probably 30 minutes or so this time, steering feel was great, everything seemed normal. I'd love to convert to the Borgenson kit, but it looks like they've been out of stock for a long time. Any help would be appreciated.

 

I have seen a lot of this.
Your rebuilt pump most likely has a high flow and high psi valve & spring from a more common larger GM.
Overheating definately means way too much flow.
That also fits with too sensitive.
Too much flow greatly increases the normal psi out of the pump. It will not really change the total system flow because of the control valve restriction. But the psi in the hoses and the ram skyrocket. Even just cruising down the road.

I recommend you pull you flow restriction orifice and measure it with a drill bit.
Then put a smaller one in. You can get them from Turn One.
They have excellent tech help too.

 

Great information here, I have always felt that my Borgeson power steering conversion, gave my car a little too much assist.

I have just ordered the 2.0 GPM restrictor fitting.

Does the restriction fitting get installed at the pump end or the steering box end?
It may come with instructions, but just doing some research.
Thank you,
Aflyer

 

goes on the back of the pump. when you take the original off, you should measure (gauge) the orifice diameter, and then compare it with your new one. If your new one is larger, than you're going in the wrong direction.

if you don't have pin gauges, then drill bits will serve as bogan hole gauges, provided you have the full set of fractional, wire-gauges (numeric), and the alphabets. I guess if you're just trying to find out if one is larger than the other, no need to get the actual dimensions. "drill bit goes into this one, but not into that one" is the answer.

 

rpoL98,
Thank you, I will post up what find.
Aflyer

 

The flow control orifice fitting is part #24



Internal drawing of the flow control orifice fitting, showing the small restriction orifice.

 

Have you found any information about what size orifice is in what year C3? I put a new pump in my 82 and due to too much Bubba I've not driven it much, but getting real close to driving it a lot so I'm wondering what size should be in my 82.

JT