[WIP] - 2009 Mazda RX-8 + Tesla Sport LDU

[ImportFanatiK]

Hi everyone,

I always wanted to build an electric car, and finally took the plunge last year and bought an RX-8 off a friend with a blown motor.

I then lucked out and found a Tesla sport LDU on facebook marketplace for a good price.
I managed to get the LDU up and running on open inverter..
https://www.youtube.com/watch?v=YUMFOA6nCZY

I recognize that while RX-8's are cheap and plentiful,. this is going to be a very hard road,.. because:

• Its CANBUS
• Its has a short track width

... I am now strategizing (and stressing to be honest) over how to mount it....
I realize that no EV swap is going to be cheap,. but I am still aiming to be cost conscious as much as I can here..

Considerations:

• RX8 Rear Track Width - 59.3"
• RX8 Tire diameter (18" rims) - 26"
• RX8 1st Gear Ratio - 3.815
• RX8 2nd Gear Ratio - 2.260
• RX8 3rd Gear Ratio - 1.536
• RX8 4th Gear Ratio - 1.177
• RX8 5th Gear Ratio - 1.000
• RX8 6th Gear Ratio - 0.787
• RX8 Rear Diff Ratio - 4.7
• RX8 Space with between rear body frame in trunk is 29"
• 2012 Tesla Sport LDU Ratio - 9.73:1 (18,000 RPM Max)
• 2012 Tesla Sport LDU Width - 32"
• 2012 Tesla Model S Rear Track Width - 67"

TLDR
I am currently planning to go with the last option (G) which involves customizing the rear crossmember, separating / relocating the inverter, and mounting the LDU offset towards the passenger side by 2" (resulting in one shorter and one longer axle).



Candidate Architecture A: LDU to RX8 Transmission
Strategy:
Separate the LDU from the transaxle/differential and build an adapter to connect the LDU motor with the RX8 transmission.
The LDU spins up to 18,000 RPM with factory 9.73:1 ratio factory, the RX8 first gear is 3.76:1, RX8 fifth gear is 0.83:1 and RX8 rear diff is 4.7:1, which means the final ratio could be adjusted between 17:39:1 and 3.9:1, with second gear being closest to the LDU ratio at 2.26 x 4.7 = 10.66:1.
Reference Examples:

• LDU to Mustang Transmission : https://www.youtube.com/watch?v=c9mRgLA4a6E
• Leaf EM57 to RX8 Transmission (Kelju): viewtopic.php?t=2275
• Leaf EM57 to RX8 Transmission (GarretNB - Vancouver BC): https://www.diyelectriccar.com/threads/ ... ne.209609/
• Leaf EM57 to RX8 Transmission (Dave Black / Southwest EV UK): https://www.youtube.com/watch?v=wogwaVu73Rs
• Leaf EM57 to RX8 Transmission (Surve.ev): https://www.youtube.com/watch?v=s0tiUaY-do0
• Leaf EM61 to RX8 Transmission (Indictive Autoworks): https://inductiveauto.com/project-ex8/
• Siemens 1PV5138 to RX8 Transmission (Damien Maguire): https://www.youtube.com/watch?v=V7JURE3DVRY
• unknown motor to RX8 Transmission (Electric EV8): https://ev8electric.wordpress.com/

Pros:

• It would save me from having to hack up the trunk and rear suspension
• It would be nice to keep the RX8 6 speed transmission

Cons:

• Would need a machinist to build the adapter.
• I think the margin of error for the adapter would be extremely low and TBH I can't quite visualize how the motor would mate with the transmission.
• Less room under the hood and for batteries. (and transmission tunnel cant be used for batteries)
• LDU inverter needs to be relocated.

Conclusion:
Viable


Candidate Architecture B: LDU to RX8 Drive Shaft
Strategy:
Purchase this adapter kit for $3,856 USD, and then mount the LDU in the engine bay:
https://amprevolt.com/products/drivesha ... 6434002996
It would need to include a new gear set that adjusts the LDU to 4.1:1.
This would mean the final drive ratio would be 4.1 x 4.7 = 20.6:1 = 116kph top speed @18000 RPM (according to http://www.csgnetwork.com/speedcalc.html)
Otherwise, the drive ratio would be 9.73 x 4.7 = 45:1 (which would be crazy high end power with very low top speed - 60kph?)
Reference Examples:

• None

Pros:

• The alignment doesn't need to be extremely precise because the drive shaft joints can compensate.
• No need for custom machining of parts.

Cons:

• Motor will need to be offset,. and I don't think there is room in the engine bay. I think it would interfere with the suspension etc.
• Less room under the hood and for batteries. (and transmission tunnel cant be used for batteries)

Conclusion:
Not Viable - wont fit and top speed is too low.

Candidate Architecture C: LDU to RX8 Rear Differential
Strategy:
Separate the LDU from the transaxle/differential and build an adapter to connect the LDU motor (mounted in/around the trunk or rear subframe) with the RX8 differential.
This means the final drive would be 4.7:1.
Based on this calculator..
http://www.csgnetwork.com/speedcalc.html, the Tesla factory top speed at 18,000 RPM would be 203kph on 26" tires.
With a 4.7:1 final ratio, it would then be 476kph,... with no very little low end power..

Reference Examples:

• GLELEC 30/70 kW to RX8 Rear Differential (Berlinger - Latvia) - https://www.diyelectriccar.com/threads/ ... ct.137578/

Pros:

• Room for batteries under hood and in transmission tunnel

Cons:

• Need to have an adapter machined between LDU motor and the rear diff (or to a very small drive shaft).
• Brutally slow acceleration

Conclusion:
Not Viable - poor acceleration


Candidate Architecture D: LDU to RX8 Axles (Model S Subframe + Widebody kit)
Strategy:
Use the Tesla Model S rear subframe.
Reference Examples:

• Full custom subframe in RX8 (Nick Ciparro / ev.rx8) : https://www.instagram.com/p/Cqlmfb5uQ8i/
• 350 Z:

Pros:

• Don't need to build a custom subframe.

Cons:

• Would have to build custom shock mounts (and geometry?)
• The Model S is wider by around 4" I think. The wheels would stick out...

Conclusion:
Not Viable - I don't want to deal with a widebody kit.


Candidate Architecture E: LDU to RX8 Axles (RX8 subframe)
Strategy:
Modify the factory subframe to accommodate the LDU. Cut the rear trunk / spare tire area.

Reference Examples:

• This guy did it with an RX7 (FD). But that is a wider wheelbase. viewtopic.php?t=1244
• This guy did it with a BMW https://www.youtube.com/@LeoW38

Pros:

• Room for batteries under hood and in transmission tunnel
• Higher margin of error as axle axle can vary a little.

Cons:

• Need to have custom axles created
• LDU needs at least 32", but clearance between rear upper control arms is 31.5", and RX8 frame is 29".

Conclusion:
TBD - would be very tight.....


Candidate Architecture F: LDU (Reversed) to RX8 Axles (RX8 subframe)
Strategy:
Modify the factory subframe to accommodate the LDU. Cut open the area behind the rear seats.
Reference Examples:

• I have seen this done online with a Porsche boxter

Pros:

• Room for batteries under hood and in transmission tunnel
• Better weight distribution

Cons:

• LDU wont clear rear suspension.
• Would have to remove rear seats (LDU would cut into rear sear area somewhat)

Conclusion:
Not Viable - I want rear seats,. and don't want to move suspension mounting points.


Candidate Architecture G : LDU to RX8 Axles (RX8 subframe + inverter relocation)
Strategy:
Modify the factory subframe to accommodate the LDU. Cut the rear trunk / spare tire area.
Relocate the inverter using this kit for $1650 Euro (https://evshop.fr/en/home/357-tesla-lar ... asing.html). This means the LDU motor will fit within the subframe, but it will have to be offset towards the passenger side by about 2" (instead of having the differential in the exact center). One axle would be slightly longer and one slightly shorter (like many FWD cars).
Reference Examples:

• None

Pros:

• Room for batteries under hood and in transmission tunnel
• Higher margin of error as axle axle can vary a little.
• Less customization needed for subframe. Body Frame doesn't need to be cut, just trunk / spare tire area.

Cons:

• Need to have custom axles created
• Need to purchase inverter relocation kit
• Differential center point offset by 2", could have some amount of torque steer.

Conclusion:
Viable



My current plan is to pursue option G (custom subframe and relocated inverter)...
Will post progress if I manage to progress further..

[arber333]

I would not separate LDU inverter from motor. It was not designed for that. You may create undesirable effects EMI or even kill inverter in the long run.

RX8 was made for very low engine - Wankel is low hanging, and you cant fit anything other than electric motor on its transmission. Here we have done several conversions of RX8 with various electric motors on transmission.
- Leaf gen 1 and 2 motors with chevy Volt inverter
- Emrax 228LV motor with 900A inverter (sorry i was mistaken about motor dimensions from 268...)
- indigenous ACIM motor with custom inverter

Mostly we fit batteries in front and under the location of the fuel tank. I have seen one guy cut into the rear trunk and fit one battery row there. This would mean you must use the motor in front then.

I have yet to see RX8 with GS450h or GS300h inplace of OEM transmission. Maybe you could try with that since it would be a better fit and still good power.

[ImportFanatiK]

I would not separate LDU inverter from motor. It was not designed for that. You may create undesirable effects EMI or even kill inverter in the long run.

Thanks, I hadn't considered that.
I will fully rule out Option F (installing it into the subframe in one piece) before I move forward with option G (inverter relocation).

[arber333]

Thanks, I hadn't considered that.
I will fully rule out Option F (installing it into the subframe in one piece) before I move forward with option G (inverter relocation).

What about the option you didnt consider yet...:

1. Mount the LDU in the front lengthwise as far inside the tunnel as possible
2. Connect the rear facing halfhshaft to Mazda driveshaft so that you can get the full Tesla speed from the motor that way
3. You fix the front facing halfshaft by some transverse shock mounts and construction to fix the torque from one side.

You could do that without hugely expšensive kit you just need to think on how to transfer that torque from the front...maybe making a bracket and weld the front shaft directly to it...

See if your project will allow such a setup

[ImportFanatiK]

What about the option you didnt consider yet...:

1. Mount the LDU in the front lengthwise as far inside the tunnel as possible
2. Connect the rear facing halfhshaft to Mazda driveshaft so that you can get the full Tesla speed from the motor that way
3. You fix the front facing halfshaft by some transverse shock mounts and construction to fix the torque from one side.

You could do that without hugely expšensive kit you just need to think on how to transfer that torque from the front...maybe making a bracket and weld the front shaft directly to it...

See if your project will allow such a setup

I have to admit that's pretty creative and I hadn't thought of that.
So the engine speed would effectively double,. but I could just drive around in 5th gear instead of second.
Its similar to option B though in that the engine bay is too small to fit the LDU when its offset to one side (since it has to sit on one side so the axle points down the middle towards the drive shaft.
Also, it means I still have the drive shaft, transmission, and motor taking up space in the engine bay, leaving less room for batteries.
It also means Im adding to the car weight without removing anything (the Mazda diff and transmission are still there).

Ultimately I have convinced myself that separating the inverter is the easiest path here.. I only need to extend the 3 phase wires by about 6 to 12 inches so it can sit just above the motor pointing upwards rather than sideways pointing to the passenger side.
I have a milling machine and a welder so I think it should be pretty easy to make some coolant passage adapters that adapt to the hoses.
My thinking is that extending 3 wires and 6 coolant hoses by less than a foot should be easier than trying to change the suspension geometry.
The inverter came off pretty easily tonight. I have added a bit more info on the inverter removal process here:
viewtopic.php?t=5138

[rjmcdermott81]

I think it would just be faster to buy my FD . But I guess I'm partial.

[ImportFanatiK]

Well I have made some progress recently,..

I designed and 3D printed a goofy stand for the LDU inverter so it wont tip over while its waiting for its new home:

and bought some aluminum blocks to machine some coolant adapters with:

but then,... I spotted an 85kwh Tesla pack of facebook marketplace this week for what seemed like a good price.
Stupid me I rolled the dice and jumped on it.. In hindsight though,. I think it is probably a pretty bad pack...
More on that story here:
viewtopic.php?t=5181
Dismantled the pack tonight on the driveway in about 4 hours with some high voltage gloves from amazon and some serious butt clenching..

Hopefully I will get lucky and there will be at least 6 that are viable. Fingers crossed...
If anyone has any good articles or videos to watch on testing these modules please do let me know.

[ImportFanatiK]

Well,.. the whole battery thing turned out to be a big emotional roller coaster for me.
10 of the modules had some small amounts of rust/corrosion on them and I had a big freak out worrying that the modules might spontaneously catch fire in the garage and take my house with them...
Between selling some and giving a few away, I ended up with 6 seemingly viable modules for a total cost of $1800. Not enough for 400V obviously,. but enough for test fitting and learning how to make the BMS work.

I also decided I may as well chop up the aluminum battery tray into little battery boxes that I can mount in the engine bay and where the gas tanks were etc.
Will have to weld up a top but at least it gives me some boxes that are already about 60% done.
Two doubles, and 5 singles.