EPAS in my Mirage

[Blueovalz]

Perhaps not very relevant to the Mantas on the forum, but maybe it will be useful to some.

Recent track days have been painful in that old rotator cuff repairs have been re-damaged, and now I've got to find a way to ease up the steering effort on my Mirage. My choice after some discussion with another member and some YouTube video review, is the Prius EPAS mainly because without the usual inputs to the EPAS control module, this system goes into a Fail-Safe mode, which appears to be a constant assist rather than one based on vehicle speed, etc. I will try to provide as much documentation as possible for those that may wish to replicate it in some fashion or another (my Mirage has significant changes under the dash from the norm).

Part of my problem is that the steering rack I'm using is a 911 rack, which is has a tight ratio (1.5 turns lock-to-lock), requiring high effort, but very responsive to input. I am also using a 930 (or >'75 911) steering column due to its simplicity and compact size. This is what I'm currently running in regards to a steering column:


The Prius EPAS ('04-'09) which I immediately cut up to see what potential it had for being shortened from the OEM length of 17", to a required length of 9" (Porsche column length), or 11" including the quick-release mandrel:


Comparison of the two columns to determine what was needed to shorten the shafts to get down to 9":


Under-dash structure with the Porsche column removed, and the EPAS mocked into position:

[Blueovalz]

Fabricated a structure to hold the EPAS in place, but it will need to be reinforced as their is still some movement of the unit as I apply torque to the steering shaft at the wheel. It was really a lot easier than I first imagined, BUT, it still hasn't be tested on the road. From what I can tell it appears the effort required to turn the steering wheel is now about 1/3 or perhaps even less thant what is was prior to this modification. Will need to insert an ammeter to get some idea of what the current draw is, and then the required wire gauge for this. I would rather not use the 8 AWG wire that is currently used on the motor pigtails. May also instead find a way to clamp the end of the electric motor in place rather than reinforce the mounting bracket. That would probably provide a more effective means of limiting any motor-torque movement.

Some photos:

.090 steel sheet structure to mount the EPAS column:


Part of that structure bolted onto the EPAS:


EPAS mounted and being tested in the car:

[Blueovalz]

Ammeter came in today, so I hooked it up, and at full lock, the maximum current draw at the motor is 22 amps. I ended up boxing the mounting bracket to create a more rigid mounting system, and then mounted the control module that came with the column adjacent to the column.