GM P/S pump --> Porsche rack modifications

I've been playing around with modifying the GM pump (as Turn One does) to match what the Porsche rack expects. So far (no track days for a few months here so i haven't REALLY tested it...it's snowing!) the feel after driving for several hours is great. It doesn't feel over-boosted and it isn't boiling the fluid.

Here is what i did:

Unscrew the pressure hose. Unscrew the piece that the pressure hose connects to. Out will pop this guy:
(stolen images, i didn't take pictures)
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Disassemble it. Inside you will find a little spring. Stack TWO thin machine washers (i actually used some tiny little lock washers) against this spring. There is also a piece that fits inside the spring--grind a tiny bit off the end (to prevent if from bottoming against the washers). Reassemble.

This is to increase the pressure. Alternatively, you can also buy the entire assembly from a Z06 Corvette from the dealer for around $40.

Now on to this guy:
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Enlarge the existing hole with a 9/64 drill bit. I have read that you can go as large as 5/32, but was told not to go larger. I went 9/64. This will increase flow.

That's it! This setup has excellent (stock) "feel" to it. I can't guarantee that it won't overheat on the track, but after some extended driving i couldn't be happier.

For the record i originally only increased the pressure, and it occasionally felt overboosted. The flow modification is also necessary, i think. Feel free to experiment for yourself

Also--it's been said before, but use Mobil1 Synthetic ATF instead of P/S fluid.

I like this a lot! Cheap and easy!

Check daily for the large brown spot on the driveway.
I haven't seen a viton o-ring rebuild kit for these racks.

Because of the Mobil1 Synthetic ATF?

The Porsche rack seals can barely handle the regular PS fluid. I'm not sure that the rebuild kit I've seen has N-buna O-rings even. When I go to rebuild mine it will get all Viton O-rings.
If you don't get the Flow rate and the pressure matched with the rack, you will get erratic steering especially at higher speeds even though you may not notice around town/parking lots.

Most people recommend ATF over power steering fluid for the 944's. Here's a company that rebuilds them (quick google search):

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Fluids
For the 924s, 928, 944, 968 use a quality brand name Dexron type II or III (you do not need synthetic types, there is no advantage using synthetics)

Most people on Rennlist agree, and so does the manual! Transmissions don't require Viton o-rings, why would a rack and pinion? They're (ATF vs. PS fluid) essentially the same thing from what i know, just different additives.

Anyways, i'm not going to claim that i got the pressure "exactly right"...but i've been on two 200 mile round trips so far this week, at speeds up to 85mph, and never once did i think that the power steering wasn't quite right. It's got a VERY good feel! The PS pump should technically just level off at a certain pressure and bypass, so i doubt it would change much with vehicle speed. My biggest concern would be at a track day--if the p/s pump is moving too much fluid it might overheat and boil over. I'll find out next season

At any rate, it's 1000% better than an un-modified system, and i'm all ears if someone comes up with a different result! The information i posted is the way to modify pressure and flow, so everyone is free to experiment.

Just a little update here:
The pump started making some funny noises, so i don't think it's quite right. If someone is going to do this i would recommend making the hole smaller than i did.

I ended up just ordering something from Turn One. Brand new GM pump, modified correctly, shipped to my door with a nice billet pulley for $310--nobody can beat that

Hey Porch - what did you do about the GM PS Pump to Porsche Rack powersteering lines? Custom made?

Yeah, those were easy!
Take each end (the GM pump connection and the Porsche rack connection) to a hydraulic shop and have them crimp a 3-4' rubber hydraulic hose on one end. Take it home, mock it up, cut it to fit, mark the orientation, and then take it back to have the other end crimped on!

I just rebuilt my 944 PS pump in less than 1 hr for $20 to my door.....LOL

Thanks MN944S

^ Yeah, but the parts to swap one of those 944 pumps on to a LS/LT motor probably cost as much/more than a nice Turn One pump! And the 944 pumps aren't that great to begin with.

Also, my p/s pump can handle hydroboost when the time comes

Yeah those damn Fluid dynamics always get in the way.....
Get the pressure right, then flow is altered....then Vice Versa