924Board.org

[ideola]

OK guys, I got the first pieces back from Chris Marsh yesterday, and mounted them up on the UWB chassis. So far so good. The fit is flippin' amazing. This setup uses two brackets that bolt onto the early cross member, and allow a non-modified 924S/944 power steering rack to bolt right onto the cross member. This also requires swapping the early knuckled steering shaft to the 924S/944 shaft, which is shorter by a couple of inches.

I am 90% certain this will work as-is with absolutely no problems on the UWB, as I have less to worry about clearance-wise due to the removal of A/C, stock coolant tank, CIS, etc. The next step is to see whether or not there will be any clearance issues on a standard 924 or 931 with A/C in place.

In terms of the pump and reservoir, my plans are to replace the stock 931 coolant reservoir with a 944 fender-mounted unit, which will open up space on the LHS frame rail for mounting the pump, reservoir, and an electric drive motor. You can get an idea of this by looking closely at a couple of the pix below with the pump sitting on the frame rail.

That will all be Stage 1, which I plan to attempt on the 941. I don't know yet about mounting of the pump on an NA, as I haven't looked closely enough, but it will probably need to be done a little differently due to the stock air box.

Stage 2 will be to work on controlling the electric motor. Current ideas are simple driver-selectable on-off switch, an inverse square circuit that would reduce motor speed inversely with wheel speed (less assist at high speed, more assist at low speed), as well as controlling motor speed using PWM driven from a capable ECU.

For now, here are some pix (click for higher resolution):




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erstwhile owner of just about every 924 variant ever made

[Martijnus]

looks great I like the stage 2 plans!

I don't like power steering at all, but I've never driven my 24 on the track and I understand it could be fatiguing. (if I spelled that word correct...)
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"Rule: Turbo's make torque, and torque makes fun." (C. Bell)

924 "50-jahre", 1981.
MSII/extra, LPG, ITB's, 5lug.
To be turbo'ed in a while.
Killed her at the Nurburgring, Porscheless at the moment

[mgatlag]

yea baby!! Keep going, it's looking awesome!!
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Michael
'77 1/2 924 N/A- 5 speed Audi box
'04 Ford Taurus - gone!!
'92 Jeep Cherokee Laredo - gone!!

Porsche... better than tea with Miss McGill
(Slap Shot)

[ideola]

[bass gt]

Dan,

very impressed!! A little snippet for you. Apparently, the Mercedes A class has an electrical power steering system. I remember a car mag over here putting PAS onto an old Ford Capri, and they used the Merc pump unit, and were very happy with it. Might be worth looking into??
Whats the lock to lock ratio on that rack?? It also looks like you could easily adjust the height of that rack, thus dialling out as much bump steer as possible. VERY INTERESTING!!!

Steve
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Front Wheel Drive is the Devil's work.

[ideola]

Steve, I looked into a wide array of so-called electro-hyrdraulic pumps. The biggest challenge I have here is that most of those are in cars in Europe. About the only ones I could readily and cheaply find here in the US were the early 90s Miatas and the current Minis. Finding a good pump for decent money turned out to be a bigger challenge than I thought.

Plus, there are at least two significant advantages to the approach I am currently pursuing:

1. With the electric motor and the pump itself, I can play with pulley sizes to achieve whatever drive ratio I want, and this can be modified somewhat on-the-fly as well. For example, I could have one pulley configuration for street driving, and when I get to the track I could do something entirely different. Just one example.
2. With a DC motor, I can variably control the voltage which will control the RPM of the motor, which will allow me to vary the speed of the pump. Virtually everyone of the stock electro-hydraulic units I researched had microchips that controlled the operation. In most of the retrofit how-to articles I found, the microchip was simply bypassed for single stage speed anyway. Integrating the microchip seemed like a more difficult challenge, in particular, with an afermarket ECU. While my approach is more primitive, for sure, it should be easier to execute, not to mention tune with inexpensive trial-and-error.

Then of course, there's my funny way of wanting to keep as much as possible "in the family". The thought being, if one is going to get a steering rack from a donor 924S/944, it's no big deal to snag the pump while you're at it, while sourcing the electro-hydraulics would be more work and higher cost.

As for the steering ratio, I don't know off the top of my head...I'll see if I can dig it up on Clark's Garage or something...

{EDIT}
There was one other unknown variable, and that is that the power steering racks are somewhat "mated" to the pump...I was concerned that the Miata pump, for example, did not operate at the same pressure levels as the stock 924S pump, and would affect the overall operation of the system. I have been unsuccessful so far in finding any model-specific information regarding the operating pressure of the different systems. All I know is that there is not a universal standard for operating pressures, that the P/S pressures are VERY high, and the each system is designed with specific pressure relief thresholds in order for the system to operate correctly over a wide range of RPMs. Too many unknown variables, so the best path seemed to be to keep a complete system intact, particularly since they're pretty easy to obtain.
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erstwhile owner of just about every 924 variant ever made

[bass gt]

Dan,

Tahts why i mentioned the Merc A class pump. Apparently, it is a totally standalone pump & resevoir, so you can mount it where ever you like. Is the A class available over there?? Iwould think so. It might be worth looking into ifit savesyou mounting an engine driven pump.

Steve
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Front Wheel Drive is the Devil's work.

[ideola]

[bass gt]

Dan,

From memory, it's the unit from the early version 1 cars.

Steve
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Front Wheel Drive is the Devil's work.

[Lizard]

cmon Dan, grow some arms!

lol I have a 320mm steering wheel on my 928 with NO power steering, but a PS rack. I am running 8.5" up front with sticky tires, no issues, even on the track! I may have slightly more difficulty running my 18x11 up front on slicks though. Heh, think about it 315 racing slicks on all 4 corners of the 928, maybe even reshell the rear so I can get a 335 under the rear!

But just so I have this right, you are dropping the booster for more brake feel,,,, but then adding PS. tsk tsk tsk
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3 928s,

[Slam]

Nice work, Dan. How much will having the rack sit forward from the crossmember affect bump-steer? This kind of application in reverse may find some friends in the 944 set. What I mean is, adapters so standard 924 racks can be fitted to 944 crossmembers. Seems to me 924 racks are cheap and plentiful compared to standard 944 racks (as opposed to power assist). I'd love to put a 924 rack on my 944.
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'84 944 - kid blew motor
'83 944 - resting comfortably. For 12 years
'87 944 - sideswiped by trucker
'80 924 - gone
'78 924 - gone
'77 924 - rusting comfortably

[ideola]

[ideola]

[ideola]

[morghen]

very interesting !!

i'm in for a copy of this thing as i also drive my 24 in the city and its a nightmare with fat tires, bump steer and no PS.
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