Last update: Jan 21 2019

Advice and Recommendations

I learned a lot by converting this car to electric. Some things worked out really well and others I would do differently. Here is my advice from the perspective of having completed the project.


The motor adapter design I used has some drawbacks.

Here are some ideas for addressing these issues.

System Voltage

Use a minimum of 70 (3.2V) cells with a DC system. I used 50 cells which is not enough to compensate for voltage sag and back-EMF.

Keep the ECU and Harness Intact

I found that my car contained an immobilizer that was not happy without the ECU and caused a problem with the remote door locks.

In a car with fly-by-wire throttle, the cruise control is implemented in the ECU. It might be possible to keep the cruise control feature if you keep the throttle pedal connected to the ECU and use the existing electronic throttle body to control the motor controller throttle.

Keep the existing wiring harness intact as much as possible. This makes it easy to locate wires. You might want to connect to the existing wiring harness at a spot that seemed unlikely at the beginning of the project.


Consider using an automatic transmission. My car sometimes gets into a harmonic surging and bucking mode that is alarming and tricky to get out of. Driving the car smoothly requires skillful knowledge and routine left foot braking. The problem is due to slop and flex in the driveline working against the rotational inertia of the motor and flywheel. This issue prevents me from allowing anyone else to drive the car without an awkward explanation. I suspect the surest solution is the damping effect of the fluid coupling in an automatic transmission.

The TCU communicates with the ECU. Therefore, the ECU must stay and be provided enough signals to keep the TCU happy so that it does not go into fail safe mode.

If using an automatic transmission, the motor needs to idle. In that case, I would consider using the original alternator, power steering pump and air conditioning compressor. Reusing these accessories requires fabricating a mounting system and imposes a small tax on the available power and range. But the wiring is significantly simplified and there would be no need for a DC-DC converter. There would be a significant cost saving for power steering and air conditioning. Electric A/C is expensive and complex.


Locate the charger outside of the cabin and trunk. Chargers get very hot. Possible locations are under the rear seats and under the hood.

Use the biggest charger you can manage. You can compensate for limited range by charging away from home. A large charger makes that option much more viable. For example, I would use the PFC5000 rather than the PFC2500.

Power Steering

I would investigate using a column-mounted electric power steering system rather than the electric-hydraulic MR2 system. This kind of system is common - for example the Subaru BRZ uses it. Space is tight under the dash in the 2006 Impreza, but if such a system could be used, it would save space under the hood and reduce overall complexity.

Fabrication by Bolting vs Welding

I recommend using bolts rather than welding wherever possible. I had some of my aluminum structural components professionally welded because I felt it would be stronger and neater than bolting. Welding metal pieces tends to draw them together, causing shrinkage and distortion. I was aware of these issues but did not anticipate the magnitude. My margin for error was usually completely used up. In other cases, angles I intended to be 90° ended up 89°. Bolting things together is more precise and easier to adjust after making design mistakes. These issues affected by battery boxes and motor controller mount.

Manuals and Parts

Get service manuals at wrxinfo.com and other documents at techinfo.subaru.com. Find Subaru part numbers at parts.subaru.com

Dealers with low part prices: generalmotorsparts.com parts.com quirkparts.com subaruonlineparts.com

Subaru Impreza Weight

Impreza models prior to the USDM 2002 (Bugeye) are significantly lighter than later models.

Impreza Weight

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