# Planning a 1996 Miata conversion: high performance, modest range



## mshobe (Jan 6, 2014)

Hello all,

Been lurking a bit and like so many before me, I now have a passionate goal to turn a good ICE-powered vehicle into a great EV. My goal is to exceed the book performance of my current '96 Miata M Edition 0-60 (target sub-6 seconds), while maintaining a modest range goal of 50-75 miles of "normal" driving. Other considerations:


AC motor with regen
Use existing transmission
strive for 50/50 weight distribution, front-and-rear
no need for A/C, but performance braking and suspension are desirable

I have scoured EV West's product listings and something like their 818 Kit as starting point makes sense, but perhaps with a Dual motor like this - to get closer to the original ICE power output?

I've seen some of the other Miata threads and it looks like a lot of custom fabrication for battery placement and motor mounting is ahead of me, and I'm also unsure of exactly what sort of adapter plating I need to cook up to mate the motor to the stock transmission. I'm also unsure about how to drive the existing 12V system from the new battery pack, and how best to fire up a performance brake system. Let the learning journey begin!


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## Kevin Sharpe (Jul 4, 2011)

mshobe said:


> I now have a passionate goal to turn a good ICE-powered vehicle into a great EV.


Welcome to the forum 

Can you tell us what your budget is for parts? Also whether you'll be doing the work yourself or paying someone else? This has a huge impact on the solutions that we propose


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## mshobe (Jan 6, 2014)

Sure thing - sorry for the obvious FAQ misses on my part. I look forward to help + advice!

Let's call the total electric powertain acquisition, mounting and adaptation budget $15K, and labor set to just engine removal by a qualified shop - the rest is meant to be totally DIY. Fortunately I have access to an excellent DIY garage here in Seattle (theshopclubs.com) and mechanic consultation as part of that membership.

Now, since the Curtis 1238e-7621 HPEVS Dual AC-34 Brushless Motor Kit - 96 Volt dual motor I originally linked to is, itself, $7900, that $15K is going to get near the limit fairly quickly with too many mistakes if that's the power level I'm going for. I also mentioned EV West's 818 kit as a very rough punch list but with something stronger than an AC-50 as the motor.


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## Moltenmetal (Mar 20, 2014)

Hi and welcome-

If you can afford the dual motor, it'll be easier than Frankensteining an OEM EV transaxle into the car.

Assuming you re-purpose OEM batteries from a Leaf or Volt or Tesla etc., you should be able to stay within your budget- depending on your range goal that is.

Best of luck- an electric Miata will give you a serious sore face from EV-grin-itis...


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## Kevin Sharpe (Jul 4, 2011)

mshobe said:


> Now, since the Curtis 1238e-7621 HPEVS Dual AC-34 Brushless Motor Kit - 96 Volt dual motor I originally linked to is, itself, $7900, that $15K is going to get near the limit fairly quickly with too many mistakes if that's the power level I'm going for. I also mentioned EV West's 818 kit as a very rough punch list but with something stronger than an AC-50 as the motor.


OEM components are a fraction of the cost of these 'old school' solutions... for example a complete Leaf drivetrain can be had for ~750 USD and that's already delivering 300HP 






Personally I would look at using the BMW, Leaf, or Tesla drivetrains with a third party inverter. If you're unwilling/unable to modify the suspension then keeping the existing transmission with these motors is also an option although personally think it's pointless dragging around a shifting transmission 

With regards to battery's both Leaf and Volt packs are available at low cost (750-3500 USD) and should provide the building blocks to meet your range and performance requirements. Have a look at Damien's latest project to see the Volt packs being used in anger


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## mshobe (Jan 6, 2014)

Kevin Sharpe said:


> With regards to battery's both Leaf and Volt packs are available at low cost (750-3500 USD) and should provide the building blocks to meet your range and performance requirements. Have a look at Damien's latest project to see the Volt packs being used in anger


Which project/thread is Damien's? Sorry I'm not quite clear on who the key players are here yet. :^)

I'm definitely interested in saving money where I can, but the real goal of this conversion is preserve the spirit of the Miata while improving its actual performance (not really its range). If I can get there with Leaf hardware and updated software, I'm cool with that.


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## brian_ (Feb 7, 2017)

mshobe said:


> Which project/thread is Damien's? Sorry I'm not quite clear on who the key players are here yet. :^)


Damien's main project is this one: Tesla Powered BMW E31 8 Series by "_jackbauer_"
Don't believe usernames  Except mine.

I suppose by Damien's "latest project" Kevin means this one:
1,000 Euro EV Build


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## brian_ (Feb 7, 2017)

Kevin Sharpe said:


> Personally I would look at using the BMW, Leaf, or Tesla drivetrains with a third party inverter. If you're unwilling/unable to modify the suspension then keeping the existing transmission with these motors is also an option although personally think it's pointless dragging around a shifting transmission


I agree that an electric motor in the engine location and keeping the stock transmission is bulky, heavy, and leaves little room for battery. On the other hand, I have seen no indication that anyone will be able to fit an OEM complete drive unit (motor with transaxle) into the rear of a Miata NA chassis. For balance (mass distribution), a Leaf unit would be great in a Miata if you could do it.

Damien quickly gave up on putting his Tesla drive unit into the back of the much larger (than a Miata) BMW 8-Series, and switched to a completely different and much less advanced suspension from another BMW model (and modified that suspension's subframe to fit the car) which did not get in the way of the drive unit. This sort of challenge sounds a little extreme for a first-time builder.

_Nuts&Volts_ is working on putting a Leaf unit into the rear of a Nissan 300ZX, which is substantially larger than a Miata and has a different rear suspension which allows more room for the motor... and we don't know yet if it will go in.
300ZX Electric Conversion

Similarly, _chrishazell_ is planning to put a Tesla drive unit in the rear of a Skyline (which has the same suspension as the 300ZX):
Tesla Powered Nissan r32 skyline


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## Duncan (Dec 8, 2008)

Speaking as somebody who back in the mists of time stuffed a Lancia Beta twin cam unit into the front of my mini (real one not one of those huge BMW things) then I would say that you would have no real problem is putting a Leaf unit into the back of your Miata

You may have to source an early Leaf where the inverter is not mounted on top of the motor - or make up some plates to mount it elsewhere


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## Kevin Sharpe (Jul 4, 2011)

I'm a electronics guy not a car guy and rely on other peoples expertise... that said, I meet little resistance from car guys when we suggest dumping the ICE transmission and changing the suspension systems... here's just one of the examples I love... a 'small' Tesla drive unit in an early Fiat 500 

*IF* you have no option but to keep the old transmission then I'd look at the BMW i3 drivetrain which I understand can be easily separated into its component parts. Obviously people are also doing the same with the Leaf drivetrain but I understand that's more complex.

What I think is important for the OP to understand is that OEM components are much cheaper than the bespoke components that we've used historically.


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## brian_ (Feb 7, 2017)

Duncan said:


> Speaking as somebody who back in the mists of time stuffed a Lancia Beta twin cam unit into the front of my mini (real one not one of those huge BMW things) then I would say that you would have no real problem is putting a Leaf unit into the back of your Miata.


My guess is that this assumes that there is "no real problem" with replacing the front half of the rear subframe and substantially modifying the suspension.

To put this in perspective, the Lancia twin cam from the Beta is a small inline 4-cylinder transversely mounted engine. The Mini came with a very small inline 4-cylinder transversely mounted engine. The Lancia unit is definitely bigger and not designed to fit the oddball Mini transaxle (which sits under the engine), so this would not be an easy swap, but the two engines are more alike than they are different. They're certainly more alike than a Miata diff and Leaf drive unit.

I think it will be great if a Leaf drive unit can drop into the back of an NA Miata with nothing but some ball peen hammer work on the floor and fabbing up a couple of brackets. I just don't think it's safe to assume that will happen, and in all of the projects described and discussed in this forum - including several NA or NB Miatas - I haven't seen anyone fit a motor in the back, let alone transversely. If anyone finds an example, please share it.

Try a web search: has anyone ever put a EV drive unit in the back of a Miata? It's great to be the first, and if something is ever done someone has to be the first to do it... but that doesn't mean you should jump off a building while flapping your arms and count on being the first to fly that way before hitting the ground.


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## brian_ (Feb 7, 2017)

Kevin Sharpe said:


> I'm a electronics guy not a car guy and rely on other peoples expertise... that said, I meet little resistance from car guys when we suggest dumping the ICE transmission and changing the suspension systems...


I'm a car guy and IT professional, but acknowledge and respect the experience of others in both fields. As a car guy I realize that when an object is bigger than the space where you want it, you must move and modify stuff; it's not like computer coding, where there are no physical space limitations. The code to describe an elephant can be stored in the same location as that for a mouse, but a real elephant just doesn't fit in mouse hole. 

One thing I appreciate in both fields is the range of work already done by others and available to build on; it's essential in electronics, in coding, and in automotive systems. For instance, Kevin's Telsa-powered VW is using a complete suspension from an aftermarket supplier that bolts into the stock bus body and doesn't interfere with the Tesla drive unit. Is there a Miata motor-mounting rear subframe waiting out there in someone's catalog?



Kevin Sharpe said:


> ... here's just one of the examples I love... a 'small' Tesla drive unit in an early Fiat 500 .


I don't see any Fiat 500 suspension or structure there. Didn't it fit? 



Kevin Sharpe said:


> What I think is important for the OP to understand is that OEM components are much cheaper than the bespoke components that we've used historically.


I agree that they are a better deal, as long as you can work with them. OEM motors are more compact, for the same power output; they use current technology, while most aftermarket motors are adaptations of traditional industrial designs... often obsolete even in industrial use.

What we should all understand is that a motor and transaxle with differential (the typical modern EV drive unit) is much bigger than just a traditional final drive (differential); it's also a different shape. That's not very high-tech or trendy, it's just the real world. Maybe in this case that won't be a problem, the ideally desired motor and transaxle will fit where it is wanted, and we'll all be very happy.


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## brian_ (Feb 7, 2017)

Here is the underside of an NA Miata body (just the rear part, cut off at the rear of the doors, standing nose-down):








You can see the circular spring pockets just behind (above in the photo) the axle line, but the entire suspension and subframe have been removed (it was posted by someone using the body section to build a trailer).

The odd offset hole is where the top of the fuel tank is exposed through the floor - that's prime real estate for a something like a Leaf drive unit (which sits on and ahead of the axle line), since of course a fuel tank won't be needed, and if the motor is in the rear the entire battery will likely be in the front.

The Leaf motor is on the right-hand side of the car, and in the photo there is a quarter-circular depression in the Miata's floor on that side... but that's for the spare tire which rides in the trunk, high over the suspension. Lose or relocate the spare, and that bit of floor can be modified if required, but it's already high and it's far enough back that it might only be a concern for a Tesla drive unit (which sits on and behind the axle line).

I stumbled across a diagram of body measurements and a diagram of reference locations in a discussion in a different forum (the second one apparently from the Mazda shop manual), and intended for body shops to ensure correct body panel alignment in repairs. This sort of documentation is available for all normal production cars. They show the substantial space between the frame rails, in which all sorts of good and interesting stuff can be done. 

The challenge is that none of this shows the Miata's suspension or subframe. For some projects (such as Duncan's Fiat 500 example) that doesn't matter because the builder buys or fabricates a complete suspension and subframe to suit the drive hardware being installed in the big space; for most projects that matters a lot because the car needs a suspension and one comes with it which was designed for different drive hardware.


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## Satisaii (Feb 14, 2018)

Since I have never posted here before, I will start with a bit of an introduction.

I am the engineer and technician for 949Racing / Supermiata. We have built some of the fastest and most reliable Miata race cars in North America. We are in the engineering study phase of converting one of our street cars.

The path to EV that you started this thread with is definitely the easy way to get going. Performance will be okay but you will be out enjoying your car in a reasonable amount of time. One thing to look out for here is that your 5 speed transmission is safe to about 175 ft-lbs of torque. Past that it will fail at some point. The 6 speed is slightly better; keep it below 275 and it will last indefinitely.

I am planning on going the mid / rear mount. The Leaf and Tesla small should fit without modifying the suspension mounting points. I would only need to cut the body out (a lot) and design a new rear subframe. From a few rough measurements I have done, the Tesla large will fit between the wheel wells. This will mean redoing the frame rails, subframe, and rear suspension. This should be fun, but will be a couple of years to do.

I will have a complete scan of a Miata tub sometime next week. At that point I will start doing some drawings and determine which route to take. Once I have something to post I will start a build thread on it.


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## Kevin Sharpe (Jul 4, 2011)

brian_ said:


> For instance, Kevin's Telsa-powered VW is using a complete suspension from an aftermarket supplier that bolts into the stock bus body and doesn't interfere with the Tesla drive unit.


A suspension system that we modified 

Possibly more relevant to this discussion is the bespoke system that's being developed for my friends VW Beetle conversion (here)... I don't have many details yet but last time I met the car guy it didn't seem to be a problem to upgrade the system to cope with ~350 HP 



brian_ said:


> I don't see any Fiat 500 suspension or structure there. Didn't it fit?


As I said previously most car people don't seem phased by these challenges... here for example is a mid-engined 500 Abarth built on the 'new' Fiat 500 platform


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## brian_ (Feb 7, 2017)

Satisaii said:


> I am planning on going the mid / rear mount. The Leaf and Tesla small should fit without modifying the suspension mounting points. I would only need to cut the body out (a lot) and design a new rear subframe. From a few rough measurements I have done, the Tesla large will fit between the wheel wells. This will mean redoing the frame rails, subframe, and rear suspension. This should be fun, but will be a couple of years to do.


It's good to see a well-informed and reasonable view of this situation.



Satisaii said:


> I will have a complete scan of a Miata tub sometime next week. At that point I will start doing some drawings and determine which route to take. Once I have something to post I will start a build thread on it.


Excellent! 
I'm looking forward to that.


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## brian_ (Feb 7, 2017)

Kevin Sharpe said:


> As I said previously most car people don't seem phased by these challenges... here for example is a mid-engined 500 Abarth built on the 'new' Fiat 500 platform


That's great, but it is very far from what "most car people" build. It is in an entirely different world from what someone doing their first car project, and needing someone else to remove the engine first, should consider.


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## brian_ (Feb 7, 2017)

Kevin Sharpe said:


> Possibly more relevant to this discussion is the bespoke system that's being developed for my friends VW Beetle conversion (here)...


That would be very relevant to the Miata, if only the Miata had semi-trailing arm rear suspension which leaves the entire space around the axle line and behind it completely empty for a Tesla drive unit. It doesn't. 

Clearly, the easiest way to do an EV conversion on a Mazda Miata while taking advantage of the excellent value of salvaged production EV components is to sell the Miata and buy an old Beetle or air-cooled Porsche... then presumably move the "Miata" badge over.


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## brian_ (Feb 7, 2017)

brian_ said:


> For instance, Kevin's Telsa-powered VW is using a complete suspension from an aftermarket supplier that bolts into the stock bus body and doesn't interfere with the Tesla drive unit. Is there a Miata motor-mounting rear subframe waiting out there in someone's catalog?





Kevin Sharpe said:


> A suspension system that we modified


Perhaps I misunderstood, but as I read the thread the modification to the Red9Design rear suspension was to add Tesla drive unit mounting provisions to the Red9Design subframe. Great work, but I don't recall any modification of the suspension components at all... which were designed to fit in the space available in a bus with a wide engine adjacent to the rear axle, and a transmission extending in front of the axle.

Kevin has provided great information about the whole bus build, including a photo of the Red9Design system as delivered, and with the rear subframe portion replaced by one incorporating mounts for the Tesla drive unit. The silver-coloured components (the entire suspension, plus the forward subframe portion) are the parts used as-is from Red9Design; the darker coloured component is a bolted-together prototype of a custom subframe section and motor mount... of greater complexity than any structural component built for most DIY EVs.

Again, where is that aftermarket suspension for a Miata which fits around either a Leaf drive unit or a Tesla drive unit (or a VW flat-four and transaxle)?  And again, maybe the space between the Mazda parts will be wide enough for a Leaf or Tesla drive unit, but the existence of such a suspension for the Bus says nothing about the fit in a Miata.


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## mshobe (Jan 6, 2014)

OP here. I am excited to have kicked off this discussion and really appreciate all the perspective, possible solutions, and exciting speculation. 

As a total newbie, I guess I'm still a little bit mystified at how, in 2018, specifying an EV conversion isn't a lot closer to specifying a gaming PC. I don't mean to say that I'd expect to convert *any* car into a killer EV with a couple clicks on Amazon. (I'd sure like to, though.) But I am really surprised that no one has tried harder to standardize an approach to popular, semi-modern ICE platforms, like BMW 3s, Audi TT/A3/A4, Miatas, MR2s, S2000s, and even 993/996 911s. Or just chosen _one_ with lots of available inventory and a plentiful aftermarket full of parts/accys, like the Miata, and gone deep to create an enthusiast-friendly kit that you can drop in with a couple days' labor from a partner shop/mechanic. I know http://www.zelectricmotors.com/ and a few other boutiques do something like this, but it's not nearly the DIY ethos I see and am inspired by here.

I'm still stuck at the basics –*which motor, whether to stick with existing transmission or try to find/fab a direct drive, how to do the math to get the amps/volts right, where to place the batteries, which batteries to get, how to easily support the existing vehicle's core 12V bus, how to update the throttle and instrumentation, how to wire everything together without killing myself or someone else who wants to help me with the project. Sorry y'all –*I probably should've started the thread there!

I also realize the FAQ I've outlined above is probably answered 10x over in the Forum somewhere. Maybe I should just read everything in http://www.diyelectriccar.com/forums/showthread.php/ev-information-669.html and see if it all comes together. This SEVA FAQ is pretty good, too.

My manifesto: Make It Easy-ish. I realize a DIY EV is a project that requires conviction and a bit of smarts, and is not something you can order like a hot NVIDIA GPU and an SSD drive on NewEgg. But golly, I really wish it was.


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## brian_ (Feb 7, 2017)

mshobe said:


> OP here. I am excited to have kicked off this discussion and really appreciate all the perspective, possible solutions, and exciting speculation.


Good  I was wondering if we had driven you away


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## brian_ (Feb 7, 2017)

mshobe said:


> I'm still stuck at the basics –*which motor, whether to stick with existing transmission or try to find/fab a direct drive, how to do the math to get the amps/volts right, where to place the batteries, which batteries to get, how to easily support the existing vehicle's core 12V bus, how to update the throttle and instrumentation, how to wire everything together without killing myself or someone else who wants to help me with the project. Sorry y'all –*I probably should've started the thread there!
> 
> I also realize the FAQ I've outlined above is probably answered 10x over in the Forum somewhere. Maybe I should just read everything in http://www.diyelectriccar.com/forums/showthread.php/ev-information-669.html and see if it all comes together.


That was probably the intention of that section, but it hasn't worked out that way. It is difficult to keep this sort of resource current (with either technology change or just refinement of the group's knowledge), and it is difficult to keep entries from devolving into rambling discussions rather than useful reference articles.


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## brian_ (Feb 7, 2017)

mshobe said:


> This SEVA FAQ is pretty good, too.


I suppose there's some good stuff in here, but as a recipe for a project I think it's doomed by a massive omission.


> Step 1. Determine your budget
> Step 2. Research
> Step 3. Acquire a vehicle and parts
> Step 4. Start building
> Step 5. Finish and test


Where is the step - which should be Step 0 in this list - in which you decide on your goals and requirements? Without that, there is no basis on which to make any of the many decisions which follow.

Of course there is another massive missing step: building starts with no plan or design.

I'm not just being picky. Many discussions in this forum are unproductive because the prospective builder has unrealistic expectations or no clear goals at all. For instance, you can't possibly answer the question "what's the right size of motor" if you don't know how much power you need, and you don't know how much power you need if you don't know what performance you are targeting, how much the vehicle will weigh, and how much drag the body will have.


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## brian_ (Feb 7, 2017)

mshobe said:


> As a total newbie, I guess I'm still a little bit mystified at how, in 2018, specifying an EV conversion isn't a lot closer to specifying a gaming PC. I don't mean to say that I'd expect to convert *any* car into a killer EV with a couple clicks on Amazon. (I'd sure like to, though.) But I am really surprised that no one has tried harder to standardize an approach to popular, semi-modern ICE platforms, like BMW 3s, Audi TT/A3/A4, Miatas, MR2s, S2000s, and even 993/996 911s. Or just chosen _one_ with lots of available inventory and a plentiful aftermarket full of parts/accys, like the Miata, and gone deep to create an enthusiast-friendly kit that you can drop in with a couple days' labor from a partner shop/mechanic. I know http://www.zelectricmotors.com/ and a few other boutiques do something like this, but it's not nearly the DIY ethos I see and am inspired by here.





mshobe said:


> My manifesto: Make It Easy-ish. I realize a DIY EV is a project that requires conviction and a bit of smarts, and is not something you can order like a hot NVIDIA GPU and an SSD drive on NewEgg. But golly, I really wish it was.


I'm not at all surprised. There is little difference in the physical characteristics required of gaming computer packaging, so a relatively standardized physical interface is feasible; machines of wildly different performance can use the same bus. In contrast, EVs must be physically different to suit varying requirements.

Another factor is the range of suppliers. You can count the major CPU manufacturers on the fingers of one hand. What two or three suppliers' designs would be supported by some EV standard, while everyone else is forced to match them?

How about a comparison with engine-driven cars: why can't I just pick an engine and transmission (from different manufacturers) and plug them together and into whatever body I want? Because vehicle design is just not that simple.

The list of example vehicles is interesting:

BMW *3-series* - any BMW is far more expensive in North America than the average person can buy new, expensive to maintain, and changes design every few years (so what would the kit fit?)
Audi *TT/A3/A4* - this is a VW group platform, so why not include the Golf ; again, a single generation would need to be chosen
Mazda *Miata* - every Miata conversion I've seen is unable to package the battery acceptably... it's just too small for most people
Toyota *MR2* - Which of the two generations (which share no parts)? How many of these could be converted: they were only built for a few years per generation, never sold well in that time, haven't been built for decades, and are now rare - I doubt I saw a dozen on the road last year, and some of those were undoubtedly re-sightings of the same few cars.
Honda *S2000* - Again, how many of these could be converted? They were only built for ten years, never sold well in that time, haven't been built for nine years, and are rarer than Ferraris - I haven't seen one on the road for years.
Porsche *993/996 911* - BMW, multiplied 

The Miata is an interesting case (in addition to being the candidate for this thread). The most plentiful variant is the NC, but all the attention seems to be on the NA/NB (which are generally rust-buckets now) and the ND (too new and expensive). It's also interesting because it is such a popular choice for engine swaps (due to a general perception that it is underpowered)... but there is no easy plug-and-play solution to swap in anything, there is no agreement of what the optimal engine swap might be, even the GM LS V8 swap is simpler than an EV conversion would be, and those LS swaps cost tens of thousands of dollars. For what performance level would the EV conversion be designed, and what would one of these be worth? A conversion for a specific set of goals may be quite reasonable and sensible, but there's no one-solution-fits-all answer in gas engines, and none should be expected for EV conversion.


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## mshobe (Jan 6, 2014)

"Everyone has a plan until they get punched in the mouth," said Mike Tyson. Pretty much feel that way now.

@brian_, thank you for your thoughtful, experience-borne analysis. RE: your critique of SEVA, I started this thread with step 0: beat the original Miata's performance specs with modest range requirements, while minimally disrupting the base vehicle's wonderful geometry and subsystem architecture. Also, agree the omission of the Golf was a misstep. That is the basis of the GTI, and an EV'd GTI could be a helluva lot of fun.

I would be happy to either use new OEM/Tier 1 supplier components if it didn't feel like such a Rube Goldberg contraption to assemble.

I would be happy to use a more conventional supplier a la EV West's inventory, if it actually fit the donor vehicle I wanted to offer up. At least they make it 'feel' moderately achievable to fill a shopping cart with parts, or just order a kit for a 70s-era 911 or a VW Bug, and get to work in the shop.

That's really all I want: an strong recipe and a believable path to success if I invest money, patience, time, and energy in the outcome. I don't feel cut out for any of this at the moment.

Going to go soak in the EV Information thread's depths, and see what happens.


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## brian_ (Feb 7, 2017)

mshobe said:


> RE: your critique of SEVA, I started this thread with step 0: beat the original Miata's performance specs with modest range requirements, while minimally disrupting the base vehicle's wonderful geometry and subsystem architecture.


Yes, I was glad to see that.


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## mshobe (Jan 6, 2014)

brian_ said:


> That was probably the intention of that section, but it hasn't worked out that way. It is difficult to keep this sort of resource current (with either technology change or just refinement of the group's knowledge), and it is difficult to keep entries from devolving into rambling discussions rather than useful reference articles.


Yeah, it does feel hopelessly out of date now in many of the key entries. The fundamentals of the parts list and the basic _process_ haven't changed too much, but sourcing the best build for a given goal in 2018 is clearly a different ballgame than it was in 2010 or so. Still, a very good place to start when trying to build your todo list.

I'm going to keep an eye on other active build threads and look for the latest-and-greatest there.


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## Batterypoweredtoad (Feb 5, 2008)

A thought that may work-use the Leaf motor and controller in the engine bay with a driveshaft hanging off of the back to the stock diff. You could then use a hacked Leaf controller or a hacked Volt controller (and get rid of the leaf one). Combine that with a CMax 'plug-in Hybrid battery. Put the motor, controller, and batteries in the engine bay and the weight distribution stays similar to stock. You have half the torque multiplication of the leaf diff but you would have more than double the torque of a stock Miata and significantly less weight than the leaf. Short range but should be lightweight and fun.


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## brian_ (Feb 7, 2017)

Batterypoweredtoad said:


> A thought that may work-use the Leaf motor and controller in the engine bay with a driveshaft hanging off of the back to the stock diff.
> ...
> You have half the torque multiplication of the leaf diff but you would have more than double the torque of a stock Miata and significantly less weight than the leaf. Short range but should be lightweight and fun.


As acknowledged here, the first problem (with any design putting a typical EV motor output directly into a typical final drive) is that the Miata final drive has a much lower reduction ratio than required to get the Leaf motor to its optimal speed; the Leaf uses about 7:1 reduction. The problem can be mitigated with an extreme final drive ratio gear set, but you can't get 7:1 for this unit.

One way to fix this speed mis-match is to use a Chevrolet Spark EV motor. They're relatively rare (not good for purchasing, inverter compatibility, or other support) but they were designed to run with a similar reduction ratio to that of the Miata's final drive, so they have unusually high torque output (400 lb-ft or 540 Nm).

It would only be a lot lighter than a stock Leaf due to a smaller battery; same motor, similar weight of running gear (suspension, brakes, steering), and a steel body which is not a large fraction of the vehicle weight. Leaving even the entire battery out of of a Leaf wouldn't cut the weight of the vehicle in half.



Batterypoweredtoad said:


> You could then use a hacked Leaf controller or a hacked Volt controller (and get rid of the leaf one). Combine that with a CMax 'plug-in Hybrid battery. Put the motor, controller, and batteries in the engine bay and the weight distribution stays similar to stock.


With the Leaf motor in the engine compartment, I doubt there is enough room left for a battery of useful capacity. The difference between a C-Max Hybrid (non plug-in, with small HV battery) and C-Max Energi (plug-in, with 7.6 kWh battery) is 340 pounds and 5 cubic feet less cargo space (so 5 cubic feet more battery pack). There's lots of detail in this earlier thread and documents linked to it:
_Ford C-Max/Fusion Energi battery pack_

The use of a battery from a plug-in hybrid instead of a normal battery-only EV is a good way to get stock voltage in a smaller unit - and that's what a Volt is - but can the smaller battery handle the power level required? The C-Max Energi can't run at full rated power on battery alone; Ford says the Energi battery can only handle 68 kW peak, and their specs for the engine and the engine+motor imply a peak motor output of 55 hp (41 kW).

So, what would these components weigh in total? My guess is that this would be more front-heavy than the stock Miata, but it can be calculated and should be. The motor weighs about as much as Miata transmission (and will be much further forward), and the battery weighs as much as a complete Miata engine.


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## brian_ (Feb 7, 2017)

It would be nice to see is someone can package a suitable motor in the back, directly coupled to the nose of the final drive, with the inverter beside it, taking advantage of the lack of the fuel tank for space. That would free up the entire engine compartment for battery and address the front-to-rear balance issue. _berlinger_ did this with an RX-8 (same final drive, entirely different body and chassis) in his _Latvian mazda RX-8 project_. In an early post, the builder shows the motor mounted to the final drive and complete subframe with suspension (remember, not an NA Miata), just mocked up on the garage floor.

It's not as slick as a complete EV drive unit (e.g. Leaf) in the back, but it would avoid suspension issues. I think that this configuration might be compatible with mshobe's goals, but it has two major issues:

a high-torque motor is still needed, and
there probably isn't enough room between the seats and the final drive to fit any suitable motor in this orientation.

An in-between solution is to put the motor in the transmission tunnel, shaft-driving the final drive. This would address the issue of space in the back, but not the gearing. It would also be difficult and likely impractical, as any usable motor is likely too large in diameter to fit in the tunnel.


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## Batterypoweredtoad (Feb 5, 2008)

Warning: a whole bunch of "ish" going on in the following thoughts.
(also remember that a stock early 90's miata is very slow compared to todays cars)


A stock early Miata makes 100'ish ft/lbs of torque and a Leaf makes 210'ish.

A stock Miata gear ratios are as follows:
1st 3.163
2nd 1.888
3rd 1.333
4th 1.000
5th .814
Final drive 4.1-4.3 (call it 4.1 for this).

A leaf final drive is 7.94. 

So a leaf puts roughly 1683 lb-ft of torque counting the multiplication of the diff.

Including a 4.1 diff a stock ICE Miata puts out:
1st gear: 1296 lb-ft
2nd gear: 774 lb-ft
3rd gear: 546 lb-ft
4th gear: 410 lb-ft
5th gear: 333 lb-ft.

With a 210 lb-ft Leaf Motor direct driving a Miata 4.1 diff:
Constant 861 lb-ft.

You would out accelerate a stock Miata in every gear but 1'st. You would likely out accelerate the stock Miata in first because there would be no clutch slipping to get moving an your torque would start at 0 rpm where a Miata ICE needs to be spun up to get peak torque. You would also stay in the torque peak area of the curve up to noticeably higher speeds than the leaf manages.

Weights: 
Leaf motor alone is roughly 125 lbs.
Cmax pack is roughly 275lbs as installed in the CMax. 
Combined the total is roughly 50lbs heavier than I see the Miata engine/trans combo but you get to run a smaller radiator, etc.

The discussions on the CMax battery seem to think they can handle pretty high amps, but I haven't seen anyone actually try it yet.

Fun stuff if someones willing to try it.


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## mshobe (Jan 6, 2014)

Thank you, B & B - appreciate the new thoughts & analysis.

In general the rear drive notion is a bugger in the NA Miata. I think doing that is advances the degree of difficulty well beyond what I want to do. I'm trying to take as modular and "drop-in" an approach with the NA platform as I can, while trying to meet my somewhat aggressive performance goals.

I like the idea of the Leaf motor and a Cmax battery pack (or equivalent?), along with whatever hacked controller can unlock extra power from the motor. I also like the idea of saving money.

Kerryman's thread was also super informative - http://www.diyelectriccar.com/forums/showthread.php/electric-miata-my-2nd-ev-conversion-69675.html - although I would like to know how he ended up with a dual Warp 9 setup and why it's retired. His battery placement makes sense in keeping the 50/50ish weight distribution, but I don't know that that would play with the newer C-Max LiPo pack.

If I'm sticking with the Miata NA, I'd like to go front motor + controller, rear pack, stock trans + adapter.

The "change the game" scenario would be to…change platforms! I don't actually have my Miata yet - I had an NA purchase lined up last week but it fell through. 

I forgot to mention another goal early on: it's gotta be a convertible. I want this thing to be working hard for pure fun purposes.

Crazy: would a 986-series Boxster make for better rear drive geometry - especially with a Tesla 'large' unit? Make the mid-engine setup there all about motor + battery? Or am I asking for far too much 12V electrical/OBD2 systems hassle? The good part of older series like the Miata NA is minimal electronic ego to be bruised by the removal of most of the legacy systems.


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## Duncan (Dec 8, 2008)

Hi
If you are starting from scratch what about a "Locost" type machine

http://www.diyelectriccar.com/forum...dubious-device-44370p15.html?highlight=duncan

Great fun -


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## Batterypoweredtoad (Feb 5, 2008)

I know I suggested the CMax pack, but do remember that it is going to provide a fairly low range. Its 25Ah, a Volt is 45Ah and A leaf is 60Ah with all of them being around 350V so a Miata with a Cmax pack is probably going to be half of a Leafs range. That would mean you get about 30-40 miles on a charge. Again-all of those numbers are "ish" 

The Beauty of the Leaf motor setup with a driveshaft and no transmission is you only need to find a front yoke that matches the output spline of the leaf motor and have a driveshaft made with it. That should be cheaper and far less complicated than having a good adapter plate to the Miata transmission made.


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## brian_ (Feb 7, 2017)

mshobe said:


> The "change the game" scenario would be to…change platforms! I don't actually have my Miata yet - I had an NA purchase lined up last week but it fell through.


Have you considered an NC Miata? Not the classic enthusiast's choice, but it has a substantial racing history and parts availability, there are lots of them out there (probably less rusty than the NA/NBs), the rear suspension (completely different from the NA/NB and almost the same as the current ND) should allow more room between the control arms ahead of the axle line for a drive unit, and there is more space between the driver and rear axle line than the earlier generations. The motor installation of berlinger's RX-8 (which uses the same chassis parts) might work.

Most Miata EV conversions are NA's, but most of them are from at least several years ago when NC's were new and thus expensive. kerrymann actually posted images of an NC as inspiration for the intended later "superlite" form of his NA conversion.



mshobe said:


> Crazy: would a 986-series Boxster make for better rear drive geometry - especially with a Tesla 'large' unit? Make the mid-engine setup there all about motor + battery? Or am I asking for far too much 12V electrical/OBD2 systems hassle? The good part of older series like the Miata NA is minimal electronic ego to be bruised by the removal of most of the legacy systems.


Maybe it's just the pricing of these things in Canada, but I've never understood using such expensive cars for DIY EV conversions.

As for the car... the Boxster is mid-engined, and the Tesla drive unit sits behind the axle. It might work (with the battery ahead of the axle line, in the original engine space), since the Boxster still has a strut rear suspension, but it would need confirmation.

I agree that computer systems would be a hassle.


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## brian_ (Feb 7, 2017)

Duncan said:


> If you are starting from scratch what about a "Locost" type machine
> 
> http://www.diyelectriccar.com/forum...dubious-device-44370p15.html?highlight=duncan


Somewhere between converting only the powertrain of a production car, and going full-on build-from-scratch, would be to use one of the body-and-frame kits which use the complete suspension of a production car. Without a sheet steel unibody, they could make component mounting easier. Examples include the Exocet (skeletal) and Catfish (fiberglass body) for Miata NA/NB chassis components, and the Factory Five 818 for Subaru Imprezza components (already used for at least one EV build). Of course there are also many kits in the style of the Lotus 7 (with a wide choice of suspensions) which inspired the Locost style.

Keep in mind that any small roadster designed for a front engine will have very little space between the driver and rear axle, forcing either a transverse rear motor installation (practicality dependent on suspension), a tunnel-mounted motor like the Device (competing with interior space), or a front-mounted motor (competing with the battery for the only large volume space in the car).


All of the discussion of driving a stock final drive unit directly from a motor would apply to these vehicles just as they would to a Miata (including avoiding the issue if a complete drive unit can be fit in).


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## mshobe (Jan 6, 2014)

brian_ said:


> Have you considered an NC Miata? Not the classic enthusiast's choice, but it has a substantial racing history and parts availability, there are lots of them out there (probably less rusty than the NA/NBs), the rear suspension (completely different from the NA/NB and almost the same as the current ND) should allow more room between the control arms ahead of the axle line for a drive unit, and there is more space between the driver and rear axle line than the earlier generations. The motor installation of berlinger's RX-8 (which uses the same chassis parts) might work.


I'm going to look into it. I'm not militant about the Miata vintage –*I just want the best platform for a convertible performance conversion I can find. And of course the NC's are a ton cheaper than any Boxster might be.

FWIW I did briefly consider starting from a kit - the 818, the GTM Supercar, and even the Superlite SL-C - but building those properly, especially the GTM, with qualified help all end up closer to six figures. I'd really rather do more of this myself, but on rails that make sense for a first-time converter.


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## brian_ (Feb 7, 2017)

mshobe said:


> FWIW I did briefly consider starting from a kit - the 818, the GTM Supercar, and even the Superlite SL-C - but building those properly, especially the GTM, with qualified help all end up closer to six figures.


The 818 kit is about $10K, and the Subaru parts are less than that (and less than the price of a usable base car for conversion). Since the EV bits would be the same cost as for conversion, how can a kit like this drive the price - for a truly comparable electric powertrain design - more than about $10K above using an old sports car? Yes, the GTM kit is $35 even before the expensive components (Corvette suspension and Porsche transaxle) and the SL-C starts with a $44K kit full of expensive proprietary bits, but not the 818.

I'm actually not thrilled about either using the excessively heavy and complex Subaru transaxle hanging out the back, or trying to fit a Leaf drive unit in front of the axle line in an Impreza suspension, so to me the 818 is only appealing with a Tesla drive unit (which has been done) or a longitudinal motor coupled to a high-ratio final drive. I understand why Factory Five chose this approach, but it involves several compromises. Everyone has their preferences, of course.


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## mshobe (Jan 6, 2014)

brian_ said:


> The 818 kit is about $10K, and the Subaru parts are less than that (and less than the price of a usable base car for conversion). Since the EV bits would be the same cost as for conversion, how can a kit like this drive the price - for a truly comparable electric powertrain design - more than about $10K above using an old sports car? Yes, the GTM kit is $35 even before the expensive components (Corvette suspension and Porsche transaxle) and the SL-C starts with a $44K kit full of expensive proprietary bits, but not the 818.
> 
> I'm actually not thrilled about either using the excessively heavy and complex Subaru transaxle hanging out the back, or trying to fit a Leaf drive unit in front of the axle line in an Impreza suspension, so to me the 818 is only appealing with a Tesla drive unit (which has been done) or a longitudinal motor coupled to a high-ratio final drive. I understand why Factory Five chose this approach, but it involves several compromises. Everyone has their preferences, of course.


Right, I'm going with quotes I've gotten from shops like VRaptor Speedworks, who are pro kit assemblers/fabricators, specifically looking at the GTM vs. the SL-C. (I think you can eject the 818 from the discussion, generally.) To do one of these kits *well* requires extensive time and expertise, modulo any EV specifics, so I'm trusting their estimates of $100-120K to build to perfection using whatever might be the best possible electric powertain for these kits. Haven't explored it in depth, but it's appealing as a concept. Until you check your wallet.

Will follow up tomorrow after check out a couple of Miata NCs.


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## Duncan (Dec 8, 2008)

Hi
My "Device" cost about $8k 

You can build something cheap if you go for basic - 

even cheaper would be a T bucket - basic ladder chassis and a fiberglass body 

https://www.tbucketplans.com/

The car is not the expensive part - creature comforts, fancy paint and Chrome are expensive


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## mshobe (Jan 6, 2014)

Took a look at an NC today; can't say too much about the rear transaxle spacing from my visual inspection, but this visualization:










…suggests there is possibly space to insert a "small" tesla rear drive unit there and mount the batteries up front. No idea how close that gets me to 50/50 distribution or performance goals, but it's a starting point. Transmission tunnel battery storage usage might help with this, since I will not need the transmission in this scenario.

It also has keyless remote/entry/passive security system that will need to be dealt with once the engine is gone. Not sure how much fooling the ECU will require to be assured everything is just fine, despite the ICE lobotomy.

How difficult is it to rig a controller and charger for this unit, though? I see Damien's Github repo covers the large rear and the small front, but is there somewhere else I should hunt for small rear drive details? 

Fun weekend kicking all of this around. Thanks all.


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## Kevin Sharpe (Jul 4, 2011)

mshobe said:


> How difficult is it to rig a controller and charger for this unit, though? I see Damien's Github repo covers the large rear and the small front, but is there somewhere else I should hunt for small rear drive details?


Lots of active development work on the charger by Tom, Damien, and others (see here). Many projects are using the Tesla charger and it's a great choice and widely available at low prices (see here) 

What details do you need about the small Tesla drive units? Both Jeff and I are using the small rear drive unit (see here and here). I've spun the motor with Damien's controller board and expect to be on the road in the next few months


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## mshobe (Jan 6, 2014)

Pointers to the relevant threads much appreciated, Kevin!


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