69427

Anyone know what the factory/typical pump output pressure is on C4 R&P applications? I've got a C4 suspension under my '69, and I recently picked up a used lighter weight aluminum pump off a non-GM car. I'm rigging up a test fixture to run the pump to see what its regulated pressure is, but I don't have the C4 pump "standard number" to compare to what I measure out of this aluminum pump. I would appreciate any info if someone knows what this pressure number typically is.

Thank you.

Tom400CFI

I'm curious what pump you found. I'm for this on the Kart, maybe, as I'd like to lighten the front any/every way that I can.

Sorry I don't know the spec for the pump relief valve. If this helps, I put a Chevy TBI/truck pump in my Kart and it made zero difference in the way the power steering functions. IOW if you can find the spec for ANY GM pump, I'd bet it's close enough to whatever the 'Vette's relief is set at.

Kevova

P/S pressure is test at lock or when pressure hose is blocked. 1200 psi should be in the ball park. However test is only for a moment, extended time at lock or blocked off will damage pump, hose, or gear. Running pressure maybe 5 psi.

69427

Please pardon a potentially silly question on my part. How is the system configured that would allow these two vastly different pressures (1200 psi, 5 psi)? Is there a fluid flow rate or pinion position that determines the pressure change? I'm possibly misunderstanding a key element in how these pumps work.

I appreciate any clarification here.

69427

The pump is a Type II pump out of an early 2000's Jeep. The Jeep had a steering box (instead of a R&P), and it's my "understanding" that the boxes required higher pressures than the R&P units do. I'm trying to figure out if the pumps have a pressure relief spring in them, or are they like an electric fuel pump that uses a downstream regulator to control the pressure.

Tom400CFI

All the pump does is pump oil. The oil travels to a proportional spool valve called a "Rotary valve" in the steering shaft and is then directed where needed. If there is no torque being applied to the steering wheel, the oil simply runs through the rotary valve and is routed back to tank (the pump reservoir). If the driver is applying torque to the wheel, then oil is proportionally ported to which ever side of the piston needs "assist" to ease steering. The harder you pull on the wheel, the more oil is ported to the piston.





SO, when driving in down the road, not steering, line pressure between the pump and rack/box would be basically "0"...or what ever pressure is generated by the friction of pumping oil through hoses. Kevova is right that it's probably something like 5 lbs. The line pressure between pump and rack/box will increase with increased load on the steering wheel, up to the relief valve set point when the steering action is dead headed (either at full lock or against a load it can't overcome)....then will not go any higher. Kevova is also right that holding the pump against relief will build tons of heat really fast. Don't do it for long.

In reality, it probably doesn't matter what the relief pressure is in any pump; they're all probably higher then high enough for street driving. The rotary valve in the rack/box is what determines how steering feels; it is the 'brains' of the system. For trucks w/a plow, off roading in deep mud and things like that, we might care about peak (relief setting) pressure as we might overwhelm the relief valve in those circumstances....but for most street driving, the peak pressures should be way below the relief valve setting in the pump.


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Tom400CFI

Copy. Thanks. I'll have to look at one of those.

They use a relief valve (as you've probably figured out from above)

383vett

So you need power steering for the kart. It seems to me the lightness of the kart could allow you to eliminate the pump and run a hose from the inlet of the rack to the outlet.

Tom400CFI

I might be able to...I haven't tried yet. I know when I steer it in my garage w/the engine off, it is pretty easy to steer. I still think it will be heavy at low speeds, but I should try it and see.

383vett