Last update: Jul 2 2018
In this car, 3rd gear works well driving from 0-40 MPH, 4th gear works well from 30-55 MPH, and 5th gear is good for over 50 MPH.
OEM electric cars like the Leaf and Model S have one speed transmissions. They use AC motors that turn fast, reverse electrically, and provide good torque at low RPMs with liquid cooling. They use different gearing (around 9:1) than the typical final reduction in a gas car (around 3:1).
For normal driving, power is not as important with an electric car as with gas, because of the difference in torque. The torque rating for gas engines is really a maximum rating, which you can only acheive at a specific engine speed. At low RPMs, gas engines provide very little torque compared to their maximum. Electric motors provide maximum torque at all speeds. The graphs below show the advantage of electric motor torque, even when compared to an internal combustion engine that has higher performance ratings.
In this example, the ICE has higher torque and horsepower, but only in the upper RPM range. The electric motor has more torque and power in the lower RPM range. In a drag race the ICE wins, but for normal driving the electric motor wins.
Top speed is limited by the motor maximum RPM and the driveline gearing. I never attempted full speed. The calculation below gives an estimate of 79 MPH with the WarP 11 motor. With the WarP 9, the calculation is 105 MPH.
s = 60 × r ÷ (g × f × w)
|s||Top speed in MPH|
|r||Motor maximum continuous RPM|
|r||Motor maximum continuous RPM|
|g||Transmission top gear ratio||0.738|
|f||Diff final reduction ratio||3.700|
|w||Wheel rotations per mile|
Continental ExtremeContact DW 215/45ZR17
There is no air conditioning. Air conditioning is not a big issue since where I live, summers are usually mild.
The only other feature that no longer works is the cruise control.
Starting in 1st gear is awkward. Gas engines have little torque at low RPM, so it's easy to stomp the throttle and wait for the power to ramp up. Electric motors have full torque at low RPMs so stomping the throttle jolts the driveline pretty hard. The motor controller has a setting to prevent power from rising at an insane rate.
To start in 1st gear, you must hold the brake pedal hard and press the throttle just the right amount to load the driveline and suspension with just the right amount of tension. With the huge torque, this is a nervous guessing game. The feeling that you might break something creeps in. Once you launch, the car accelerates at a blistering rate, but that only lasts for what seems like a few car lengths. The acceleration is so fast that you max out the motor's RPMs instantly. Shifting from 1st to 2nd gear for maximum acceleration is also awkward.
In contrast, starting off in 3rd gear is smooth and satisfying. The torque feels appropriate. We're accustom to accelerating quickly in 1st, then a little less quickly in 2nd, and so on. With electric, the car keeps right on pulling hard in 3rd, all the way to 40 MPH. The sensation of linear acceleration is exhilarating.
In short, I converted this car to electric for fun. I hoped this project would inspire my kids and show them that if what you want does not exist, you can make it happen yourself.
The choice of Subaru made the most sense for me. There is a strong and active Subaru community where I live. The area hosts several large Subaru clubs and there are two major annual car shows specific to Subaru.
I chose the WRX because of the World Rally Blue color and overall sportiness. World Rally Blue was only available on the WRX. Compared to the base model this car has sporty brakes, taller gearing, faster steering rate, and upgraded suspension. In order to have a car with these features (particularly the color) it is far more cost effective to start with the more expensive car and sell the very desirable turbocharged engine, than to upgrade a base model car.
In terms of the goals, this project is a great success. There has been tremendous interest in the car which has lead to quite a few interesting conversations and friendships.
AC induction motors that are available in the conversion market have the main benefit of regenerative braking, but they cost more and make less power than DC motors.
Typical charging time is 2-3 hours. A full charge takes 6-7 hours. Doing a full charge requires returning home with no remaining charge. That never happens.
The table below shows the yearly savings, which varies with the cost of gasoline. The maintenace cost is the yearly average for 10-year cost of ownership items such as oil changes, air filters, coolant flushing, timing belt.
12000mi × $3/gal ÷ 25mpg
12000mi × $0.12/kWh ÷ 2.6mi/kWh
With AC motors capable of regenerative braking, there is additional savings in reduced need for brake service.
Converting a car is a major undertaking with difficult and expensive problems. The amount of work is similar to swapping a gas engine from a different model.
Not if you've got a good working gas car. Keep driving that until it is kaput.