openinverter forum

Hi,

My name is Stefan and I'm converting an MX-5! I have been driving one for the past 8 years and I didn't feel like touching that one, so I bought another



The plan:
Model S front drive unit mounted in the rear subframe. This gets rid of the entire original driveline. This is a must have for me. I don't want to deal with any driveline issues or weak points that will break with all that torque . The Miata has a massive community that also does some 3d scanning, so I did all the fitting in Blender. The fuel tank is right above the subframe, so that is where I have room for the motor. Hence the choice for the front sdu that is already tilted in the Model S. The motor will have to turn backwards so I need to open it up to modify the oil pump and put the openinverter board in.


The added bonus: Lots of room in the engine bay and transmission tunnel to put all the batteries. I have bought a Corsa-E pack and will probably be using 16 modules to get a 96s pack and save some weight as opposed to using all 18 modules. I have not taken all the modules out yet but I assume every module has a cooling plate under it. Not sure if I will be using these. Some are very easy to handle, others not so much. I probably don't need the cooling anyway as I will have just one 3.3kW charger and I don't live in the desert. I might use electric heating pads instead for the colder days.

I have already removed the motor and most of the other ICE bits and dropped the subframe from the car.

I'm now designing the motor mounts so I can start building

Loving them straight to the point builds. Have fun!

I'm doing an NA with a model 3 motor and more or less came to similar conclusions. Are you in a country that allows for modification of the body? you will very likely need a mount at the back end of the battery box that bolts through or is welded to the chassis. best of luck with the build! I really need to finish my rust restoration and get this thing together.

edit: also, where did you get the 3d scan of the rear section? I've been trying to locate that and had to do things the hard way to make sure everything fit up well

Sooo a little update. It's been a while, but there has been progress. I have spent quite a few hours in CAD designing the motor mounts and this is what I came up with:



I got all the part laser cut and bend,welded it all in the subrframe and test fit the motor. Somehow one bolt does not quite line up, but I can fix that.




Incredibly happy with the result. It fits in the car perfectly and the differential is pretty much exactly in the same place as the original. Also, the tank cover in the car gives perfect acces to the fill plug and wiring connections on the motor. It's like it's designed to be this way .Now it's time to design the battery box

ScythianNite wrote: ↑Tue Aug 26, 2025 6:46 pm I'm doing an NA with a model 3 motor and more or less came to similar conclusions. Are you in a country that allows for modification of the body? you will very likely need a mount at the back end of the battery box that bolts through or is welded to the chassis. best of luck with the build! I really need to finish my rust restoration and get this thing together.

edit: also, where did you get the 3d scan of the rear section? I've been trying to locate that and had to do things the hard way to make sure everything fit up well

NIce! I spoke to you on Facebook messenger a while back . For the battery box, I think I will use the bolts for the front subframe and the two bolts for the rear subframe reinforcement brace. Or I might reinforce the frame rails and attach to that. I got these scans from leftlanedesign.

Awesome work! The lineup of the output shafts is outstanding and it looks like its coming along well!

Been busy at work, but also spent a lot of time in CAD on the battery box designs. This is what I've come up with so far: Most of the time has gone into making the pack as low and not-front heavy as possible.

They are two seperate boxes that will be connected with connectors. I'm now deciding where to put these and all the other components like contactors and relays. The front box will have a service disconnect at the front so I can have the positive and negative contactor in the rear near the motor. Controlling these with the OI drop in board seems to be the easiest, but I'm not sure how I would go about closing the contactors when I want to charge. If anyone wants to share how they have done this with their OI board I'm very interested

Really impressive build!
When I was converting my Mazda MX-3 i came across some people trying to convert Miata MX-5. I think from Australia. We had a debate about Mazda using transmission as a carrying member against chassis twisting in the turns. That would explain the lightness of the chassis... They said if they removed transmission car would feel like it would fold on itself...

I guess I would recommend you setup your battery box in the tunnel to resist chassis warping as well. Just relaying info...

arber333 wrote: ↑Sun Nov 09, 2025 3:28 pm Really impressive build!
When I was converting my Mazda MX-3 i came across some people trying to convert Miata MX-5. I think from Australia. We had a debate about Mazda using transmission as a carrying member against chassis twisting in the turns. That would explain the lightness of the chassis... They said if they removed transmission car would feel like it would fold on itself...

I guess I would recommend you setup your battery box in the tunnel to resist chassis warping as well. Just relaying info...

Yup you are right, its called the PPF, power plant frame. This basically makes the engine, transmission and differential one solid unit. However, the ends, the engine and diff, are mounted in rubbers, so it probably doesn't do much for chassis stiffness. It does resist twisting of the driveline under load to get a more responsive throttle feel. PPF delete kits do exist aswell for people that swap to different gearboxes or diffs. Atleast, that is what I make of it haha.

I am designing the box to add a lot of chassis stiffening though, like people do by adding reinforced frame rails and even butterfly braces. Most of it is based on my intuition though, not maths