De-powering power steering.

MetricMuscle wrote: Could someone confirm my assumption that a power steering pump does actually create suction on the return side to evacuate/scavenge the fluid from the rack back to the fluid reservoir?

I don't think it does. I think the pressurized fluid pushes its way back to the reservoir.

If you de-power a rack the right way, you will also get rid of a couple of degrees of slop in the steering.

I love my properly depowerd 2nd gen RX7 rack. to me, it is exactly as much effort to turn teh wheels at any speed. I realize that it can not be, but it seems that way to me and my wife (also depowered RX7 rack in her car)

Rob R.

MetricMuscle wrote: Could someone confirm my assumption that a power steering pump does actually create suction on the return side to evacuate/scavenge the fluid from the rack back to the fluid reservoir?

Nope. It works just like an EFI fuel system in that the stuff coming out of the return side is forced out by the pressure side. Then it goes into a reservoir, and the pump pulls from that reservoir.

This thread reminds me that I have a manual rack for my '88 FC Turbo II laying on the floor in my garage. I drove the car today, and the factory power steering is very light, quick, and twitchy. I think I'll go ahead and swap in the manual rack rather than de-power the OE rack to improve the feel a bit. It could stand a few more turns lock-to-lock and also needs a bit weightier feel, both of which the manual rack should provide.

Make sure you have the mounts and bushings for the manual rack. They are different and NLA.

Curmudgeon wrote: I don't think it does. I think the pressurized fluid pushes its way back to the reservoir.

Knurled wrote:

MetricMuscle wrote: Could someone confirm my assumption that a power steering pump does actually create suction on the return side to evacuate/scavenge the fluid from the rack back to the fluid reservoir?

Nope. It works just like an EFI fuel system in that the stuff coming out of the return side is forced out by the pressure side. Then it goes into a reservoir, and the pump pulls from that reservoir.

Thanks for the input. My main reason to re-purpose the power steering pump in my de-powered Miata was to provide oil pressure to a rear mount turbo but also to provide scavenging suction to eliminate the need for an electric scavenge pump which is necessary if oil is supplied by the engine. The idea of a self contained loop for just the turbo oil would be a plus, I'd imagine an electric scavenge pump could be added to either arrangement.

I suppose back pressure on the low pressure side of a hydraulic system will not cause seal issues like it will on a turbo bearing which will blow out the seals.

It's not "back pressure" so much as the only thing getting the fluid from the rack to the reservoir is the supply of fluid behind it. (If you blew out a pressure line, the pump isn't going to suck the fluid up the return line)

P/S pumps, also, really don't like it when you feed them foam. The oil coming out of a turbo is foam.

Would it be possible to convert a PS pump into a scavenge pump? Machine the internal area around the impeller so as to create vacuum and lower the pressure capability? I suppose y'all would like to see what the inside looks like, I'll get some pics.

Thanks for waiting patiently for me to get back y'all. Sorry, no pictures but it is basically a vane pump which should be able to pull vacuum the way it is. I'll have to experiment and see if it will do what I want it to.