[DRIVING] 1993 FD Rx7 with Tesla LDU and ElectricGT Batteries

[rjmcdermott81]

The car - Like many of us...I've always dreamed of owning a 1991-1993 RX-7. To me, this car looks amazing, BUT I've always stayed away from it because of the unreliable rotary engine. And honestly, now that I've driven it I'm not very impressed. Part of that is because I have an automatic and the gearing sucks but in stock form it doesn't really feel that fast. So, I figured, if I'm going to electric swap a car I should start with one that really needs it.

The challenge with this build is getting the rear-mounted drive unit in an independent rear suspension car. As you'll see getting this sucker to fit while maintaining the integrity of the rear subframe is my first big hurdle. I think for a fabricator or hotrod shop this may not be too difficult but I'm a novice so it's going to take some thinking and trying.

To catch everyone up here's the plan (things will probably change as I go): 1993 FD RX-7

Motor: Tesla Model S drive unit (motor, inverter, and single-speed gearbox) rated at 362 hp and 325 ft⋅lb or more
Batteries: Chevy Volt or some other option
Color: Red, white, or maybe BMW Long Beach blue? more on that later...
Timing: I want to take this car to Radwood Austin 2021 under it's own power. If I had to it repainted by then that would be amazing but I don't think that's possible.

I tend to get into projects one step at a time. Make commitments and complete small jobs. So first step was...just buy an RX-7. In 2019 here is where the market was:

Non-running, half stripped cars: 12-15k
Decent looking, running automatics: 15-19k
Decent looking, running manuals: 19-22k
Good looking manuals: 22k+

After finding so many issues with my e30 that had been sitting for years I really thought paying a little bit more to get a running and decent looking car would be worth it. So I searched high and low and finally found a 93 auto in Tallahassee, FL for 17k.

Here are the pics from the ad





I talked to the seller at length and he described it as in good running condition with an older repaint. We agreed on price and I paid using escrow.com (I highly recommend). I decided to fly out there and drive it back because....that is always exciting.

Plugging in my current project plan for tracking:

[sfk]

You might want to consider using the Lexus GS450h transmission instead of rebuilding the backend of your FD to fit a Tesla drive unit.
The Lexus transmission will be a lot cheaper, and should fit in the existing drive tunnel where your auto box already is. And wouldn't upset your weight balance so much?

[rjmcdermott81]

This research is a bit dated (1 year old) but I used it to decide on how to control a Tesla LDU.

I chose opensource route myself because of cost, customizability, and longterm flexibility, but each option seems to have it's merit.

Open Source (Ebay + EVBMW)

• Control Method: EVBMW PCB
• Total Price (Base Drive): $4,140*
• Total Price (Base Drive + Quaife): $6,140*
• Total Price (Performance Drive): $5,140*
• Total Price (Performance Drive + Quaife): $7,140*
• Includes:*
  • Damien Logic board: $739.20 shipped
  • Used Tesla drive unit (Base): $3,000 shipped
  • Used Tesla drive unit (Performance): $4,000 shipped e46 Pedal: $100
  • Low voltage wiring/miscellaneous: $200
  • Optional Quaife Differential: $2,000
  Comments: This options requires you to do quite a bit of research on your own and support is provided by the Openinverter forum. It isn't plug and play out of the box. Prices estimated based on Ebay auctions September 2019.
  
  If you get into a jam Damien offers paid support in a few forms - single email (€10), 30 minute support call (€60), or a full day (€450).

HSR Motors (057 Technologies)

• Control Method: Outside controller talking to Tesla board
• Total Price (Base Drive): $7,999
• Total Price (Base Drive + Quaife):
• Total Price (Performance Drive): $10,999
• Total Price (Performance Drive + Quaife):
• Includes
  • (1) Large Tesla Drive Unit - BASE (refurbished)
  • (1) 057 Technology Drive Unit Controller
  • (1) Accelerator Pedal (Dual hall-effect)
  • (1) Basic low-voltage wiring (controller, motor, pedal, etc)
  • (1) High-voltage wires with connections for drive unit
  • (1) Instructions, pinouts, protocols for controller, etc
  Comments::

EV Controls

• Control Method: Outside controller talking to Tesla board
• Total Price (Base Drive): $6,799*
• Total Price (Base Drive + Quaife): $8,799*
• Total Price (Performance Drive): $7,799*
• Total Price (Performance Drive + Quaife): $9,799*
• Includes:
  • The EV Controls T-1C Controller that communicates with the inverter over the CAN bus, and will allow you to do the following;
  • -Engage drive, neutral and reverse modes via the 7″ touchscreen,
  • -Adjust peak power output and regenerative braking power levels via the touchscreen,
  • -Display the following data on the 7″ touchscreen;
  • -Drive mode (D, N ,R)
  • -Traction pack voltage (HV)
  • -Inverter 12V supply voltage
  • -Accelerator position
  • -Stator current
  • -Actual power in kilowatts, positive or negative (regenerative braking)
  • -Max power limit
  • -Max regen power limit
  • -Five internal inverter temperature readings
  • -Vehicle speed (user adjustable scaling to account for wheel diameter)
  • -Current brake pedal and regen state
  • -Diagnostic data.
• $3499 for everything listed above.
• Comments: Requires pedal and low voltage wiring added to the price.
  
  I don't see customizability to other gauges so I believe you need to be satisfied with the 7"" screen output.
  
  Limited to S-85 and P-85 drive units

Stealth EV

• Control Method: EVBMW PCB
• Total Price (Base Drive): $7,800
• Total Price (Base Drive + Quaife):
• Total Price (Performance Drive):
• Total Price (Performance Drive + Quaife):
• Includes: Tesla Base Rear Drive Unit: Drive units removed from Tesla Model S and Model X vehicles with less than 25,000 Miles. Each drive unit houses an AC induction propulsion 3-Phase/4-Pole motor that can spin up to 16,000 RPM in large drive units and 18,000 RPM in low power and front drive units. The housing also includes the controller w/ Inverter and differential. Each drive unit comes with our own Stealth EV Controller Board replacement that allows for CANbus communication with any BMS, VCU, Hall Throttle, and switchgear. Wi-Fi access also comes standard for “in the field” or “on the fly” controller adjustments, no longer requiring USB connectivity or proprietary equipment.
• Comments: Appears to be a drive unit with the EVBMW (Damien's) board installed. Requires pedal and low voltage wiring added to the price.

Zero EV

• Control Method: Replacement PCB - based on EVBMW but further customized by Zero EV
• Total Price (Base Drive): $12,159
• Total Price (Base Drive + Quaife): $13,509
• Total Price (Performance Drive): $17,086
• Total Price (Performance Drive + Quaife): $18,436
• Includes: Large Standard Drive Unit, Zero EV Control System, Open Diff, Drive Shaft Stumps, Display, Throttle, Gear Selector & Low Voltage Junction Box with Loom.
  
  Options:
  • Performace Large Drive Unit 150BHP increase £3,995
  • Quaife ABT Limited Slip Diff (Highley recommended) £1095*when bought with drive unit kit.
  • Quaife Spool Locked Diff (for drif/ off road use only) £750*when bought with drive unit kit.
  • Drive Unit Coolant System Upgrade £795
  Comments:

EV West Drop in Unit

• Control Method: Outside controller talking to Tesla board
• Total Price (Base Drive): $11,900
• Total Price (Base Drive + Quaife):
• Total Price (Performance Drive):
  Total Price (Performance Drive + Quaife):
• Includes: Includes: Tesla motor, inverter, gear box, dash display and control unit (EV Controls), throttle pedal, throttle pedal plug and pins, brake switch, brake switch plug and pins, encoder plug and pins, inverter plug and pins, axle clips, 2 axles, pre-charge relay, and pre-charge resistor.
• Comments: Looks to be the EV Controls controller with a drive unit and all the trimmings to make it go out of the gate.
  
  I don't see customizability to other gauges so I believe you need to be satisfied with the 7"" screen output.

Limited to S-85 and P-85 drive units

EV Shop EU

• Control Method: EVBMW PCB
• Total Price (Base Drive): $12,165
• Total Price (Base Drive + Quaife):
• Total Price (Performance Drive):
• Total Price (Performance Drive + Quaife):
• Includes: This kit includes the Tesla motor, inverter, gear box, power cables and drive shafts. And, Damian’s EVBMW inverter board.
• Comments: Looks like they are packaging a used drive unit with Damian's inverter board installed.

EVTV.me

• Control Method: Outside controller talking to Tesla board
• Total Price (Base Drive):
• Total Price (Base Drive + Quaife): $16,995
• Total Price (Performance Drive):
• Total Price (Performance Drive + Quaife):
  Includes:
  • Tested and refurbished Drive Unit Motor/Inverter/Gearbox Assembly from salvaged Tesla Model S with Quaife ATB Differential installed.
  • GEVCU Controller with Tesla control software
  • Wiring harness
  • EVIC Tesla Display from Andromeda Interface
  • PKP2400 CAN Control Switch Panel for Tesla Drive Unit
  • IVTSCALE 1000Amp current/voltage sensor
  • Custom Speedhut CAN Gage set for Tesla Drive Unit
  Comments:

*These prices estimated using ebay prices for some of the hardware to make it a more complete solution for comparison

[rjmcdermott81]

When I got there the car looked good for it's age but it had a few noticeable issues: bad oil leak from the engine, some sort of clunking in the rear-right when lifting the throttle, and when I hooked up a boost gauge it was making 6psi of boost when the forums said 10. The seller conveniently wasn't there and I had to deal with him over the phone while trying to decide whether to fly home or just take it. I figured I wouldn't do any better with another car so I bought it. After spending more time with the car I am thoroughly impressed at how original it is. Every covering, shield, piece of plastic is where it should be. The guy said he bought it to do an LS swap but couldn't do it because of how original it was. Well...here I am about to ruin it.

Here's a shot from my 12-hour drive home. Drove it through the night with no issues other than - gas smell and no start unless you twist the key 5-10 times (apparently these are both common "features" of RX-7s).

Here she is safely at home:

Other issues I would later discover: cigarette lighter doesn't have power, slight surface rust on the inside of the rear hatch, and most importantly...the keys don't work in the door locks, or the door locks don't work at all.

[rjmcdermott81]

At this point, I started to plot and plan. I got the tesla drive unit measurements, jacked up the car, and started to measure. I'd never seen the underside of an RX-7 so at this point I was still going on blind faith that I could get something to work.

When you remove the gas tank and cut out the rear spare wheel well there is plenty of clearance in the back:



and plenty of width for the drive unit gearbox to fit if you cut the center of the subframe out:



This gave me enough confidence to buy a drive unit. Which I needed to do because without it, it would be impossible to figure out how to fit it in there. I bought it from a Tesla dismantler in CA, super cool guy and they delivered it freight right to my house. Here is unpacking day:

[rjmcdermott81]

This thing is heavy. I was stuck trying to figure out how to get it from the crate to a furniture dolly until my neighbor showed up with an idea to use 2x4s



There we go

[rjmcdermott81]

At this point I got sidetracked because my bike frame cracked and I had to repair the CF.



Which gave me the perfect chance to try out a paint color I thought might look good on the RX-7. Long Beach Blue which I saw on an M2 in a parking lot:





That paint color was shockingly cheap. So maybe.

I'm also considering white and red





I love the red but man....painting it white would be so so much easier. Now that I have a little experience painting I realize that white doesn't show any dents and you don't really need a super high gloss so the cut and buff would be easy

[rjmcdermott81]

I found a spare rear subframe on ebay for $350 and I figured it might be wise to cut that one up and leave the one in the car intact for reference. Starting to eyeball up what needs to be done:



Behold! I found somebody online doing the same thing. He posted a couple pics on diyelectriccar.com and has the driveunit mounted so I know there is a path forward

[rjmcdermott81]

When I cut this subframe in half it's going to be in two pieces. I figured the first thing I needed to do was put it in a jig. I think there are a couple of ways to do this. Were I to do it again I think I would just weld pars directly to the subframe. I chose to drill holes in barstock, attach it at the suspension points, and then weld it to a frame I built. With the idea being to maintain the same suspension points.







Experimenting with timelapse videos on the GoPro

[rjmcdermott81]

After that I added a bar across that will eventually have the motormount attached to it. I went with 1.75 DOM steel tubing that is spec'd for roll cages. I figured if it's strong enough for that it's probably strong enough for this application. When I start cutting the center section out it will help provide support.

[rjmcdermott81]

Now I'm starting to cut away the center section. Going a little bit at a time:





Even with that removed you can see there is a major issue. The motor and invertor are hitting the vertical supports for the suspension:





When I zoom in on the other guys subframe it is apparent that he's done some major major rework of this section. Nearly to the point that it looks like he's rebuilt the whole vertical piece:

[rjmcdermott81]

Sidetracked again - my son had made his pinewood derby car. I swear, he held the paintgun the whole time, but I definitely guided his hand when we put down the PPG clearcoat

[rjmcdermott81]

Back to the grind. Taking more metal away.





You can also see that I decided moving a 300# object for test fits wasn't working. I created a scale mockup of the drive-unit. Much easier to move around



I also put my sweet jig on wheels because I am lazy



Now, here is where it's at after that grinding. You can see the axle inputs on the mockup. They are forward of the suspension pillars but ~2 inches behind the stock location for the RX-7 differential. If you look at the rubber pads on the bottom of the subframe, that is where the axles typically pass

[rjmcdermott81]

Pulling it in to where it will live for the next few months. Once I start taking this thing apart it will only leave with that motor mounted.

Quick note - I got a quickjack over the holidays that runs off of 12v. It is rad. Not as good as having a lift obviously but I love it and I feel so much safer using it.



Exhaust and driveshaft out:



Shocks out:



Pulling out the diff:

[rjmcdermott81]

One thing I did before taking the car apart was have it weighed. This way I can do a direct comparison of before/after

[rjmcdermott81]

I took the gas tank out and now I'm getting a better view of the space I have to work with

[rjmcdermott81]

No mas wheel well. I expect this to be the only thing I cut on the vehicle. Truly, this would be easy to weld back in and convert everything back to ICE.







[video=youtube_share;rvG6xsRA8yo][/video]

[rjmcdermott81]

I did some final cutting on the rear subframe. At this point, I think my next step is to mock it up with the actual drive unit so I can add a cross support that will keep everything stable while I unbolt it from the jig. I originally planned to take this somewhere for final welding but...with the lockdown I'm gonna take a go at it.

[rjmcdermott81]

Small progress. I have the motor mocked up at the right level and it allowed me to figure out how much more to cut out. I have one small bit I'm going to cut tomorrow and then I'll move on to fortifying the subframe so I can take it out of the jig.

I mocked it up with the tesla axles - these things are beefy. I didn't insert them all the way but I am concerned that it's sitting pretty far back. The only way to really tell will be to get the suspension on here and look at it.

[rjmcdermott81]

Progress this weekend. I now have the two top lateral support bars completely welded in. I still need to clean up the welds more after I take it out of the jig but they are pretty much done.



My son always seems to show up at the end to check my work....
[video=youtube_share;MKzsFq07odE][/video]

[rjmcdermott81]

Alright - now I feel like this thing will have the structural integrity it needs to pull it out of the jig. This is going to hurt ground clearance so I may come up with a better design when I get it all together. Last thing I'm going to work on before I do that is installing the front motor mount.

[rjmcdermott81]

Motor mount is tacked in place.

[rjmcdermott81]

Progress! and the next hurdle - the axles.

Here is the subframe out of the jig



Test fitting the motor/suspension/axles for clearance - all good here





At this point I'm going to start finishing up the subframe so I can mount it.

Now, on the axles. I don't know squat about axles so looking for advice. This is the first time I've ever taken CV joints apart...pretty easy. The RX-7 axles are actually the right length, but the knuckle that goes into the inboard flange is obviously different. I took the knuckle off the tesla axle but it is a different spline count so no-go there.

Here is the inboard Tesla knuckle - 35 splines



The outboard splines on the Rx7 - 26 splines



Length - 20.5 inches

[rjmcdermott81]

I took the advice and cranked up the welders so I've gotten some great looking welds and some crappy looking welds. Getting ready to pop it into the car and mount the suspension and motor to create the other motor mounts.







I decided this is a subframe so who cares what it looks like. I know if I started to do it then I would go down a rathole, so, if it looks like a 4 year old painted it. Well, a 4 year old did paint it.

[rjmcdermott81]

I managed to get the motor up and the front motor mount bolted on.









I put the suspension and axles in to test fit everything. It looks like I have good clearance on the axles (these are just the rx7 axles in there for mockup purposes right now). The fit between the motor and the subframe is really close. I may have too clearance some material if I get contact. Not sure how much wiggle these motor mounts will allow.







Now that this is all looking good I am going to start working on the rear and side motor mounts.