[Akya2120]

Hello folks,

Excuse me for being new and potentially putting this in the wrong place. I'm intending for this to go from groundwork to moving vehicle in about one to three years.

I've been mulling it over for a while and I am going to start a project car. I would like to convert an AW11 MR2 to an electric vehicle. Originally I was going to do diesel, but it felt like a half measure. I want to have about 80 miles of range minimum, I want to make about 180-250hp, I plan on freeway cruising around 75 mph, I don't care about peripherals just yet (heating, ac, power steering).

My original thought was to use a zero bike motor and mate it to the stock MR2 transmission. Would make for a generally easy swap, but it doesn't quite get me to my power goals. Also, afaik electric motors tend to destroy manual transmissions when shifted (more on this later).

Then I considered using two of these motors and just mating them to the axles since the bikes are direct drive and good to 124 mph as is (I realize that's partially because of the reduction from front to rear sprocket). The hard part about this is how to control the motors when cornering (same power to both wheels will mimic a locked or welded differential). Simply using the electric motor on the transmission utilizes the stock differential and I wouldn't have to worry about that.

I also considered using a Tesla motor, but from what I understand this gets expensive quick, and I think there are more simple and cost effective alternatives that suit my goals.

Usually manual transmissions don't like the shock load from electric motors, which is what causes them to fail. Has anyone developed a shift controller that rpm matches the motor to the ground speed for a given gear? Wouldn't that remove the shock load and allow for clutch less shifting? I would imagine that would be fairly doable via a microcontroller and switched gates for the shift knob. Depending on which shift gate is triggered it would calculate and adjust the motor rpm until the gear is engaged (heck you could use the clutch start safety switch to engage the rpm matching mode). Would this still cause a bunch of shock to the transmission? I would imagine it could be fine tuned until it doesn't but then why has no one done it?

I am basically a novice when it comes to this kind of swap. I do have a lot of fabricating, design, and automotive experience. It also helps that I work in a shop and have a couple of machinist friends who I can trade work with. If anyone has recommendations and or advice I would love to hear it. Thanks for reading!

 

[Akya2120]

So the shift controller will likely come later if I decide to go the manual route. The stock 4-AGE which came in the MR2 made 115-130 HP (depending on year) and 110 Ft•Lbs. So a single zero motor is about on par with the stock engine. There was also a supercharged model which made a little more power, but probably about the same torque number as the zero.

What are my other options for motors? Should I be trying to canabalise a production vehicle like the leaf or bolt? I'd rather go with an AC motor, but I'd like some input on which motor I should be looking at, and why. I did think having independent motors for the rear wheels would be cool, but would add more complexity since at that point I need to figure out how to bias them for cornering.

 

[Akya2120]

Well, I was interested in using two motors for exactly that reason. I don't like open differential vehicles. Two motors allows me to emulate a performance differential, but then I only have a set gear reduction which may not necessarily be a bad thing.

As for the batteries, the MR2 fuel tank was in what would normally be the transmission tunnel. So a few could probably fit in there. Maybe not 80 miles worth, but at least a couple. The engine bay is rather large compared to an ev transaxle so probably a couple could go in there. It also has a frunk and a trunk. I'd like to keep enough storage capacity to pick up groceries, I'd also like to keep the vehicle as close to a 50/50 balance as possible (I have plate scales to help achieve that).

The stock engine alone weighed about 350lbs. The transmission is probably another 100, the fuel tank was a little over 10 gallons, so about 80lbs. How much does the Tesla transaxle weigh? How much does 80 miles worth of batteries weigh?

Does the Tesla transaxle have torque vectoring, or some form of limited slip differential?

 

[Akya2120]

Those numbers look reasonable for a 4A-GE, but unless there is some higher-powered version of the Zero than I found, the zero motor is not even close to that. The original (DS) and higher-power (SR) models of the Zero appear to have 44 and 67 horsepower... way short of any 4A engine. Torque appears to be 106 lb-ft for the SR, which looks close but is presumably attained at only low motor speed. Two Zero motors might be suitable.

The SR/F is the model with a 140 Ft•Lb and 110 HP motor it also has a 14.4 kWh battery pack. It seems like I would want about a 30 kWh battery pack to meet my range goal, but that's estimated from current ev ranges and battery packs. The other thing I like about using two motors is I have no transmission or differential to service. The zero motors are passively air cooled, which means I'd have to run a duct or a fan. Either of those things are not a problem. The hard part is going to be (once again) power biasing for corners. Or I could just run it like a welded diff and it would just be real drifty all the time haha.

 

[Akya2120]

I like the idea, it gives me an idea that I think is even more useful. I'd try and mount the motor up front, then just use the trans tunnel for the driveshaft. I'm sure I can find an IRS diff second hand or in a junk yard. I'm not extremely familiar with all the details of modern motors but I understand their operating principles.

Can anyone tell me, what is an efficient motor around 250-300hp/~180-230kW output? Likely most modern EVs are going to be my choice. Is Tesla the best choice for weight, performance, and efficiency? Or something else?

How does one go about controlling these motors? I'm guessing it's mostly just hardware that gets bought and calibrated. Does it make more sense to buy a totaled Tesla/Chevy/Nissan/BMW to get the batteries and motor, or hunt for them somewhere else?

Using the engine bay for batteries does seem to make sense since likely, unless I chose to have very short range, there will be more weight in batteries than motor. Do the batteries and motor get liquid cooled?

Sorry for all the questions, I'm familiar with this stuff but not on the level of the minutiae that allows it all to function cohesively. If someone has a good article or three to read, that would be awesome. Thanks for all your help so far folks!