Prius electric power steering

I was hanging out with a few Cobra owners at this year's vintage grand prix. The topic of power steering came up and two of the guys showed me their set up using the electric power steering units from a Toyota prius.
The units are under $300. on ebay.
The owners claim its a very easy install, 'just had to fab a backing plate to mount through the firewall.
I've never heard of it until now but I'm guessing it must be pretty common based on how many units are listed.
Have any of you installed one of these?

I have installed an 05 Chevy Equinox electric steering unit in my car.  Very similar to the Prius unit.  Mine is combined into the steering column, not on the firewall.  That doesn't really matter, the operation is the same.

The Prius unit will operate in "fail safe" mode with no other inputs.  This is what makes it so popular.  There are other units from other brands that are the same as the Prius.  Can't remember them right now.  There are videos on YouTube that go into better detail on those units.  

All these electric units have variable boost that is controlled by the cars computer.  Boost is usually tied to the cars speed.  In fail safe mode, the Prius units only operate at one fixed boost level, as do all the other units in fail safe mode.

I chose the Equinox unit because there is a guy on EBAY that sells a boost controller for that unit.  It is self contained and plugs into the same jack that the Equinox's ECU plugs into.  A small potentiometer (variable resistor) that can me mounted anywhere controls the boost level.  I have not driven my car yet, but I have tested the steering.  The controller works as advertised.  There appears to be 3 levels of boost adjustment.

Now for the possible downsides.  Many people that I read about doing the Prius type conversion complained that there was no feel in the steering.  It operated fine, but had no road feel.  That is the main reason I went with the Equinox.  So I could lower the boost level if needed.

Another issue that was reported is failure to return to center (RTC) after a turn.  RTC is how a proper steering is supposed to work.  After a turn, normal steering will try to go back straight on it's own.  I have some theories as to why this happens with the electric steering.  All of the cars I read about were factory manual steering cars from the 60's.  These cars had high steering ratios and very little caster to make steering effort low.  The electric steering units, like the Prius, are basically a right angle worm drive with an electric motor.  This type of drive is more or less self holding.  The Equinox unit has considerable drag when trying to turn it from the output side.  The Prius would be the same.  This drag acts like a brake on RTC.  I purposely added a fast ratio steering rack (15 to 1) as apposed to the stock MII 20 to 1 ratio.  I also added about 6* off caster instead of the 1-2* of the stock MII.  This should greatly increase the RTC force and hopefully eliminate the reported RTC issues.  Those 2 things should also make the car more fun to drive.

FWIW - I did leave room for conventional hydraulic steering if I don't like the electric stuff.  Aslo, the vendor with the EBAY controller also has a unit that uses GPS to alter the boost level for speed.  I wanted to be able to do my own adjustment.

Thanks Hotrod,
That's the info I was looking for. The return to center was my biggest concern. Just knowing that there are units with boost control has me anxious to get started on this project.

One other thing. When you get your unit, be sure to get as much of the power wiring as you can. The units I have seen on EBAY do not appear to have any of the external wiring.

The Equinox unit has a special connector with a #8 power wire (may be a #10) and ground wire. This needs to be connected directly to the battery with a Maxi fuse. I used a 50 amp. The unit will not turn on until the boost control unit is powered up.

Also, the Equinox has a short driveshaft on the output side that connects to the Chevy steering rack. Get this if you can. It might come in handy for your setup. Mine was made like a driveline shaft in that it was made from tubing with welded on yokes. I shortened mine and used it to connect to a short pass through I made for the firewall.

Good luck.

Thanks again,
Luckily found that my "go to" salvage yard has 3 equinoxes (they were unsure of available parts when I called.
I'll be checking soon.
This will probably end up being my winter project so it's time to start rounding up parts.

Here is the vendor (I think) that I got my controller from.

Some Equinox units won't work.  

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