groovyjay

Has anyone tried using the Flaming River (or others) Variable Pressure steering Pump with the steeroids Rack n' pinion? IMO one of the problems with the Steeroids is the lack of feel and input you get at higher speeds. With the Variable Pressure Pump you could have more "feel" to the system, or am I missing something. I'm currently building my own R n P system for another project, but this would be for my 79 which already has the steeroids installed.

Any thoughts?

http://www.flamingriver.com/index.cf...rod/prd278.htm

mrvette

AS I RECALL, Jim Shea made a comment about this once, saying something bout a variable output pump is not the best solution...or maybe not work at all....not sure...he thought better to change the valving internal to the rack...but I dunno how to do that....MY setup is fine...I have no complaints...

maybe I just used to it after 4 years now...

GENE

Guru_4_hire

Arent there various sport model grand ams out there that have the sporty road feel?

Techno

Thats why I have manual steering.

mrvette

YES, there are, all I know is the rack I got from the junkyard was a fresh one to the car, no leaks, and none yet..AFAIK....
so was it a GM rack by a dealer? aftermarket? valving? all unknown....

all I can say is,....it's 2.7 turns lock to lock and runs/feels good to me...

but the HUGE releif of not constantly fighting the whell over these Florida sand based, turck rutted roads may mask my understanding of anything else....the comparo is THAT large...

course I have '92 vette wheels/tires all around, so that accentuates any road input to the steering that a 15 inch 60 series tire ever would be able to generate...

GENE

groovyjay

Gene, did your rack originally come from a 92 Grand Am? Thanks for the input, I hope to hear what Jim Shea has to say about this...

Jim Shea

You can get variable power assist by adjusting the FLOW from the pump. I know that this sounds counter intuitive, but it is true. No steering systems change pump output pressure.

The best type system of variable flow system is to electronically control the pump output flow as a function of vehicle speed. (i.e. the faster you drive the less steering power assist you want.)

Saginaw had variable assist power steering of this type on the original uplevel Saturns; some of the Jeep Grand Cherokees (1996) and on the full size pickup trucks, Escalade or Denali SUVs around 1998-99.

The theory behind EVO is that at parking and low speeds you try to flow as much oil out of the pump and through the steering gear control valve as the pump will put out. The high oil flow makes the hydraulic valve very responsive and the steering effort feels light.

As the vehicle picks up speed, a computer controller sends a signal to the EVO valve on the pump that causes it to divert more and more oil back into the pump rather than flowing out to the gear valve. The computer puts out a pulse width modulated (PWM) signal to the EVO valve. With the lower flow, the steering control valve becomes less responsive and the steering feels heavier.

GM vehicles had the EVO software integrated into the chassis controller. However, the 1996-97 Jeep Grand Cherokees had a stand alone EVO controller box.

Now the next problem is that you need a signal from your Corvette to the EVO controller box in pulses per mile. Our C3 corvettes have a speedometer cable and do not have any speed related electronic signals.

I think that some aftermarket cruise control kits include some weights that are attached to driveshaft on the car. Some type of magnetic pickup then counts the weights as the rotate. This signal then is fed to the cruise control as a vehicle speed function.

This above type EVO variable assist system is the high end unit.

A lower performance, lower cost system utilizes an internal valve inside the power steering pump that reduces the pump output flow as a function of pump speed. We called them "droop flow" pumps. Many Japanese pumps and a very few Saginaw pumps have such internal control.

Here is the problem with this type of variable flow system. As your vehicle accelerates your engine rpm is increasing and decreasing as you go through the gears. If you radically change the pump flow with pump speed, you will feel your steering effort changing as you change gears and the engine speed changes up and down. So the mechanism in the pump cannot radically change pump flow.

I drove many Japanese vehicles with droop flow systems back before I retired from GM and Delphi. I would take a car up to 70 mph and then slip it into a lower gear in order to change engine rpms. I would steer from one lane to another and I tried to detect changes in steering effort. At speed I also shifted the transmission into neutral and allowed the engine to return to idle speed. As the car coasted, I tried steering lane to lane while slowly changing engine speed. I never tested a car where I could really detect any real change in effort with droop flow.

This is the type of pump that the Flaming River add is refering to. They are not correct in describing it as a pressure changing pump.
I would be very surprised if there is any appreciable change in steering effort with their pump.

JIML82

groovyjay

Thousand thanks Jim, you're the Daddy with this stuff! If I was using electric speedo, I could use the 97 Jeep pump then and make it work easily?

mrvette

Yes, '92 GA, with the lower powered 4 cyl engine, as I recall....

I used the hoses and everything with a 88 vette serp drive pump, and reservoir....

GENE

lostpatrolman

Jim, would the Jeep Cherokee stand alone controler work to control and escalade pump? Also, can you edit the controler to tailer the flow rates to your liking, sort of like you can do with electronic transmissions?

Jim Shea

The Jeep controller can be used with the EVO valve on the Escalade pump. You don't need the entire Escalade pump you just need to unscrew the EVO valve from the back of the pump. Remove the discharge fitting from your Vette pump. Screw the EVO valve in its place. (This presupposes that you will have clearance behind your pump to fit the EVO valve.) The EVO valve does take up more space.
Just use the truck EVO valve do not use the flow control valve from inside the truck pump. The Corvette flow control valve is set for a maximum pressure relief setting of 1100 psi. Truck pump have pressure relief settings of 1450 psi. The higher truck pressure relief will most likely cause your Vette hoses to leak.

I don't know what type of speed signal the Jeep controller requires.

The Jeep system also had one other input beside vehicle speed. It had a steering wheel rotation sensor. The sensor was part of the steering column. I doesn't have to be fitted on the column it just has to be plugged into the controller box.

I did find this information in my files: The EVO valve was designed for a 250Hz PWM signal, modulated between 5% and 95% to get a 12 volt signal.

You might be able to design a simple on/off circuit that would trigger the EVO valve to minimum flow at 25 mph for instance. This might allow you to get around a controller box.

bebezote

Thanks for the info earlier Jim via PM..much appreciated..

has anyone tried this yet? got the rack attack from VBP...and wanting to try this if possible..

Denpo

Jim, do you know if such EVO setup would work alongside an hydroboost?

Jim Shea

Just a guess. It probably would work with Hydroboost.

BTW, I had almost forgotten all the EVO stuff I published in this thread almost 9 years ago. I had forgotten a lot of it. Maybe I should gather it up and publish it on Terry Rudy's Corvettefaq site.

I did evaluate a number of Japanese and European cars with droop flow (engine speed variable output flow) pumps. This was when I was working at Saginaw. (I have been retired for 13 years now.) Back then, I never found any competitor power steering systems where I could detect a change in steering effort or response with engine speed variable (droop flow) pumps.

Jim

69427

I've been curious how much power a typical pump consumes. I've been kicking around making a controller that would open the bypass more during high speed/RPM/WOT. My main focus was trying to reduce the fluid heating, and perhaps free up a slight bit of horsepower on the straights when there's minimal need for steering assist.

Jim Shea

If I remember correctly, driving straight down the road the power steering pump consumes about 1/4 horsepower. It is hardly worth spending much money on trying to reduce that small amount by another small percentage.

Electric steering assist will substantially reduce that 1/4 horspower down-the-road figure but it will cost you a couple thousand dollars.
Jim

69427

Thanks Jim. Given how hot the fluid gets at times (and the reports of occasional system damage when tracking our cars), and the greater use of p/s coolers on vehicles these days I've always been under the impression that pumping/circulating the fluid through the higher pressure bypass position significantly heats the fluid, and that heat energy has to be provided somewhere in the form of horsepower drain. As I mentioned earlier, I'm mainly focused on reducing the heat build up and preventing rack wear/damage. Can you give me a better understanding of the causes of the heating?

I always appreciate your technical input here.