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1996 Miata Conversion - Finally Some Traction (Sorry, Bad Pun)

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The motor adapter plate and hub arrived about 3 weeks ago from CanEv, which prompted me to pull the trigger on starting on the conversion. Nothing too remarkable to say, other than everything is harder and takes longer than I would like. I'm working outside under a canopy, thank g-d for that, we had record breaking temps here in SoCal the last couple of weeks.


I broke a 3/8" drive extension while trying to remove one of the bell housing bolts. It relented after I switched to a 1/2' drive and breaker bar.

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Hyper 9 with mounting plate, and original flywheel and clutch mounted, ready to install.

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I'm using the motor mounts from the original Miata ICE. I have 4 braces that are between the adapter plate and the face of the rubber shock mount. I'm not sure this is a good idea, I'm pretty sure the braces I made are probably inadequate. The braces are made from 3/4 in tubing with a 0.070 wall, mild steel for sure.

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I mocked up fitting 2 of 3 Tesla Model S batteries in the engine bay. I have enough depth to stack two modules in the back. I will have a battery box with rails to support the modules properly on the tongues that sick out on the long sides of the modules. 2 More batteries will fit where the gas tank used to be.

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Getting ready to remove unnecessary sheet metal to make way for 2 more Tesla Modules.

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Nice view of the rear diff! I've got to secure a plate here and stack the balance of the 2 battery modules here. I will probably end up about a half inch higher that originally. I really hope the convertible top will fold down fully. More later...

While I figure out how I will improve my motor mount, I spent time finishing battery module mounting behind the front seats.

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1/8 inch aluminum plate.

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Back rail secured to the 1/8 inch aluminum plate. It's hard to see the groove in the rail. Tesla battery modules have a tongue that stick out about 3/16 of an inch. I put the groove in the rail so that the battery module is lifted above the plate by a fraction. The second battery sits on top and also floats by a fraction above the lower battery. Also there are 4 slots that will be used to have a couple of ratchet binders strap down the battery modules to the aluminum plate.

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As expected the battery modules sit about an inch higher than the original shelf, but the top still folds down. ( I just tried to upload a photo with the top down, got a warning that I have exceeded 10 images. Really, there is a limit? There must be a work-around)

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I mocked up fitting 2 of 3 Tesla Model S batteries in the engine bay. I have enough depth to stack two modules in the back. I will have a battery box with rails to support the modules properly on the tongues that sick out on the long sides of the modules. 2 More batteries will fit where the gas tank used to be.

Nice view of the rear diff! I've got to secure a plate here and stack the balance of the 2 battery modules here. I will probably end up about a half inch higher that originally. I really hope the convertible top will fold down fully. More later...
Nice photos and setup on the batteries. I've debated cutting that metal around the gas tank for a little more room for my Leaf modules. It would be nice to keep them in groups of 12, maybe this is the way!
 

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Discussion Starter · #3 ·
The height of that space is just about 6", maybe 5-3/4 ". And that space can be made contigious with the trunk. So if you are willing to give up some trunk space, you might get all the space you need.

Mine is clearly never going back to what it was. I spent a few hrs trying to remove the section of the wire harness that feeds the ECU. I thought if I did that there would be room for a couple of 2 ought cables that connect the rear battery bank to the front. I pulled out about 1/3 of the wires out without removing the dash, and at that point the rest must be tightly taped to a different section of the wire harness, as no amount of pulling would extract them. At this point I am not pulling the dash, but I probably will have to later for different and more gauges. I think it will be a lot easier to run those cables along the Power Plant Frame (PPF). I have been searching for this conduit ( https://new.abb.com/low-voltage/products/conduit-fittings/harnessflex/range/conduit/evo-conduit ) but no one seems to carry it. Too bad you are not on the Big Island. Our daughter lives near Captain Cook, we get over there every now and again.
 

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I'm sold. It pretty much doubled my capacity in that space. I'll cut today, maybe mount.

I know exactly what you're talking about with the ECU and harness. If I recall, it is just tape. I went in there with a knife and freed it, no dash removal needed. Might have been a zip tie too. And I'll pull the dash when I get everything else done and can work on instrumentation. Nice link to conduits... I've seen them somewhere... LegacyEV?

Let me know if you have a long layover at HNL! Hopefully I'll have things together and bring Miata1 for a quick meet!
 

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View attachment 132453

I'm using the motor mounts from the original Miata ICE. I have 4 braces that are between the adapter plate and the face of the rubber shock mount. I'm not sure this is a good idea, I'm pretty sure the braces I made are probably inadequate. The braces are made from 3/4 in tubing with a 0.070 wall, mild steel for sure.
This motor mount won't last more than your first acceleration or speedbump. I'd suggest you try and find a shop that can weld you something substantial. Click to see
suggested design
 

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This motor mount won't last more than your first acceleration or speedbump. I'd suggest you try and find a shop that can weld you something substantial. Click to see suggested design
Yeah, I'll second that. Just in general 2 problems:

1 - It's cantilevered all the way from the mounting plate, so the motor itself is just danglin'. No bueno.

2 - The tubing isn't strong enough and is folded, so you've lost most of the strength there.

It's fine for testing or measuring where you want your real mounts.

Just in general, angle iron (if you're cheap, junk bed rail) is good enough, it'll be strong in 2 directions. You'll want some kind of strap around or at least cupping the bottom of the motor and bolted to it.

Here's a $120 version you can buy, but, it's not rocket science, you can build one that fits your usage for less (and you'd have to modify this one anyway).

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You might as well keep your braces to the adapter plate (maybe replace them with angle), but for sure add some type of motor cradle.
 

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Discussion Starter · #9 ·
I appreciate the collective wisdom being offered. Once upon a time I had full blown machine shop / welding shop facilities at my disposal, but that was before I retired. Now my facilities and tools are limited. My options are contracting for fabricated items or possibly bartering if anyone here on the forum is in San Diego county or close.
 

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Discussion Starter · #10 ·
Yeah, I'll second that. Just in general 2 problems:

1 - It's cantilevered all the way from the mounting plate, so the motor itself is just danglin'. No bueno.

2 - The tubing isn't strong enough and is folded, so you've lost most of the strength there.

It's fine for testing or measuring where you want your real mounts.

Just in general, angle iron (if you're cheap, junk bed rail) is good enough, it'll be strong in 2 directions. You'll want some kind of strap around or at least cupping the bottom of the motor and bolted to it.

Here's a $120 version you can buy, but, it's not rocket science, you can build one that fits your usage for less (and you'd have to modify this one anyway).

View attachment 132610

View attachment 132611

You might as well keep your braces to the adapter plate (maybe replace them with angle), but for sure add some type of motor cradle.
This clamp might be my best option. Can you tell me the source/vendor? I had a look at the custom mount at Zappy2's web page. I have emailed him
to see if there's any chance a second could be fabbed. Thx.
 

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Discussion Starter · #11 ·
I appreciate the collective wisdom being offered. Once upon a time I had full blown machine shop / welding shop facilities at my disposal, but that was before I retired. Now my facilities and tools are limited. My options are contracting for fabricated items or possibly bartering if anyone here on the forum is in San Diego county or close.
 

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Discussion Starter · #13 ·
This clamp might be my best option. Can you tell me the source/vendor? I had a look at the custom mount at Zappy2's web page. I have emailed him
to see if there's any chance a second could be fabbed. Thx.
Actually, no. I just did a google search for "Hyper 9 motor mount" or something like that. Lots of places had them and I chose one at random. Shouldn't be too difficult. One was $119 US, one was 120eu.
Hey thanks. I actually tried using Google's image search and dragged the image into Google's image search box. Google found it right away. Worked great!. Thanks again.
 

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This clamp might be my best option. Can you tell me the source/vendor? I had a look at the custom mount at Zappy2's web page. I have emailed him
to see if there's any chance a second could be fabbed. Thx.

you can start with a generic clamp, and have a welder/fab shop add legs from the faceplate to make sure motor is lined up straight, tie to the clamp, and finish at the motor mounts. The whole thing needs to be stout to provide 3 points of contact with the chassis to provide alignment and withstand all the torque passed to the chassis.

The three points the chassis is designed for are the transmission mounts, and the two motor mounts. I would highly suggest you use those points.... and use 2"x2"x3/16 or even 1/4 wall steel square tube. Paint it when done since structural steel will rust like crazy.

I do not have any more details on who did the fabrication in CA for the mount I have. But it was designed for a DC Warp 9, so the exact measurements may not be the same for your motor anyway.
 

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Discussion Starter · #16 ·
you can start with a generic clamp, and have a welder/fab shop add legs from the faceplate to make sure motor is lined up straight, tie to the clamp, and finish at the motor mounts. The whole thing needs to be stout to provide 3 points of contact with the chassis to provide alignment and withstand all the torque passed to the chassis.

The three points the chassis is designed for are the transmission mounts, and the two motor mounts. I would highly suggest you use those points.... and use 2"x2"x3/16 or even 1/4 wall steel square tube. Paint it when done since structural steel will rust like crazy.

I do not have any more details on who did the fabrication in CA for the mount I have. But it was designed for a DC Warp 9, so the exact measurements may not be the same for your motor anyway.
Dan - thanks for the info. Having recently been under my Miata to remove the gas tank, engine, and other gas related stuff, I don't recall seeing any transmission mounts. On my NA, the transmission was bolted up to the engine, of course, but the tail end of the transmission connects to what Mazda calls the PPF -Power Plant Frame. This substantial "C" channel couples the torque from the engine and transmission to the differential. I may misunderstand, but it seems to me this PPF was designed to carry the torque load. If this is true then the original motor mounts are principally carrying the weight of the engine and transmission. Have I missed something here?

Bill
 

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... Having recently been under my Miata to remove the gas tank, engine, and other gas related stuff, I don't recall seeing any transmission mounts. On my NA, the transmission was bolted up to the engine, of course, but the tail end of the transmission connects to what Mazda calls the PPF -Power Plant Frame. This substantial "C" channel couples the torque from the engine and transmission to the differential. I may misunderstand, but it seems to me this PPF was designed to carry the torque load. If this is true then the original motor mounts are principally carrying the weight of the engine and transmission. Have I missed something here?
There are no transmission mounts, and that is possible because of the PPF, but the PPF is not carrying any driveline torque. It is a bending beam (like a bridge), not a tube (like the torque tube of a Porsche 924/944/968 or 928, or Corvette C5/C6/C7, etc). The body structure takes the torque reaction between the engine mounts and the final drive unit mounts; that's why the final drive unit mounts are spaced relatively far apart laterally, instead of just being one mount on the centreline. The PPF keeps the engine from tilting forward or backward, and similarly keeps the final drive from twisting nose-up or nose-down in reaction to axle torque, by bridging the engine (with its mounts) to the final drive (with its mounts).

So the PPF works in bending to resist drive torque to the axles; it does not work as a torque tube connecting the transmission and final drive.

Engine swaps in any Miata routinely omit the PPF, just because those swaps often change the transmission and final drive as well and the components swapped in don't have mounting points for the PPF; they add a transmission mount and forward final drive mount instead. This changes the loads on the vehicle structure, but people seem to get away with it without folding up the body, even with GM V8 swaps.

All generations of Miata (MX-5) use essentially the same PPF design.
 

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Discussion Starter · #19 ·
Incorporating the original motor mounts along with the OEM Hyper 9 base mount was just not going to work for me. I have mocked up a design of the motor mount with some wood scraps, and will hopefully head for a welding shop tomorrow. It all ended up being pretty simple. It will consist of a standard 3 inch steel channel about 12 inches long with a flat plate welded at each end at an odd angle. I am attaching a photo of my mock-up. This weldment can be bolted to the Miata frame at the same two points where the original motor mounts were attached. The feet of the motor band will be about 3/4 of an inch above the weldment. In this 3/4 inch gap I intend to put a piece of hard neoprene to give me something of a shock mount. A couple of 1/2 inch bolts will attach the base mount to the weldment, passing thru the neoprene.
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Incorporating the original motor mounts along with the OEM Hyper 9 base mount was just not going to work for me. I have mocked up a design of the motor mount with some wood scraps, and will hopefully head for a welding shop tomorrow. It all ended up being pretty simple. It will consist of a standard 3 inch steel channel about 12 inches long with a flat plate welded at each end at an odd angle. I am attaching a photo of my mock-up. This weldment can be bolted to the Miata frame at the same two points where the original motor mounts were attached. The feet of the motor band will be about 3/4 of an inch above the weldment. In this 3/4 inch gap I intend to put a piece of hard neoprene to give me something of a shock mount. A couple of 1/2 inch bolts will attach the base mount to the weldment, passing thru the neoprene. View attachment 132688
If I understand this correctly, the plan is to just clamp to the motor case, with no other mount for the motor, the motor end of the transmission, or the motor to transmission adapter. If so, that won't likely work well, because it provides no significant ability to handle torque, leaving the torque reaction to the transmission mount, which isn't intended to handle any driveline torque reaction at all.

Remember, the PowerPlant frame is not a torque tube, so all of the drive torque (motor torque multiplied by transmission ratio, even in the lowest gear) should be tranferred through motor or transmission mounts to the vehicle structure.
 
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