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Discussion Starter #1 (Edited)
Location: San francisco, CA

Budget: hopefully less than 20k for all the conversion parts and any labor costs, but realistically this will push 25k. the car itself was 18k in the end

Donor car: a 1971 corvette in January from a fellow in new jersey who restored it and modified it quite a bit (crate motor and 5 speed transmission drivetrain swap, lots of suspension work, etc)





Motor: Tesla model S P85 large rear drive unit OR Tesla model 3 performance rear drive unit. Some strategically welded arms from the ladder frame to the motor mounts should work well. This could be relatively easy or the hardest, most expensive part of the entire project. The motor 3 motor is more efficient when not under heavy load, and FAR FAR better cooling capacity BUT nobody supports their firmware yet and it isn't clear how many years it'll be until AEM will support it, if ever. Very adventurous folks like damien macguire are only now getting the thing to spin using other open source inverters, https://www.youtube.com/watch?v=ulRrUJ-2gPk


as for mounting, i was thinking this, a 180 rotated around the horizontal axis, with three mounting arms welded to the ladder frame on the front, back, and side
this will require running the motor in reverse full time, i'm sure some inverter settings will allow this
it'll also require installing a special oil pump adapter by zero EV which allows oil to flow in reverse drive https://zero-ev.co.uk/product/tesla-large-drive-unit-replacement-reverse-drive-oil-pump/
i'll need to cut into the car's fiberglass body, but i don't know how much




a very big problem is going to be the rear suspension geometry, which normally relies on a leaf spring and a sway bar system bolted to the bottom of the diff, and the half shafts actually push and pull on the diff as a suspension component, VERY BAD For a tesla motor!
I'm looking into alternative suspension systems which use coilovers instead, like ridetech's, which is $1900 without the actual coilovers.




but even with this i'm not sure if the half shafts are still active suspension components?
There's even more expensive systems like detroit steel's DECAlink which is over ten grand!






Battery: 34kw of chevy volt batteries. I'd like Gen2 but the Gen1s are half the price and only slightly lower capacity. Some in the engine bay with a battery enclosure to make it look like a V8 because yummy under hood candy, like ICON's derelict mercury EV did. the rest of the batteries go where the gas tank used to be, which may or may not hang lower and thus cause the full size spire tire sling to have to go away. Volt batteries have excellent high performance (power density) because of almost no voltage sag. They're also cheap, work very reliably, have a nice log-like form factor, and have built in excellent battery cooling. I'm hoping for 80+ miles of range.
Something like $5000 for two Volt packs in good condition.



Cooling: unsure yet, but the water pump and electrically controlled diverter valve out of a tesla. chevy volt batteries and the tesla motors have built in cooling systems so no need to screw around making chill plates.

Controller: AEM EV VCU200 https://www.aemev.com/products/ev-vehicle-control-units/vcu200 , i've heard about these for a while, and Bisi of Bisimotors used this as the basis for his electric porsche 935 project. According to him, it works extremely well and is very polished overall. My guess is all the different modules i purchase from them will add up to like, $4000





Contactor: unsure

Power steering: I really want to keep hydraulic power steering, electric pump driven. It's wasteful but it feels so much better than electric power steering. EV West makes a belt fed pump but i'll probably re-use the one that came with the car, which is a really nice Steeroids rack and pinion setup

A/C: MVP might omit this since i live in a SF and A/C is kinda unnecessary

Charger: Not sure how to get there, but i absolutely want to shoot for a level 3 fast charger which interfaces with CCS. With such a short range this feels like a heavy requirement for this to be driveable. There's some noises about CCS charging for DIY builds but this might be a wait and see, hopefully this becomes a mature thing soon (within a year).


Safety: Haven't researched much but i would really like switchable fuses between every 72 volts or so, so at any given moment during assembly or maintenance, if i make an oopsie, i only get shocked with 72v before a fuse cuts it. Also, inertial fuses so in a crash, everything is isolated from everything else. Also, a first responder safety line, mimicking tesla's implementation with a BRIGHT RED WIRE right under the hood with a really obvious label on it


Styling: a very important aspect for a classic, i'll need a wide rear track for thick tires, and some huge flares should pair nicely. I'm also a big fan of Fathom green, this really deep forest green that chevy used for only a few years. As such, the final product is going to look a lot like this, Garrett Randall track weapon project









Timeline: With the c3 now in my garage, i'm going to spend about a year maintaining it, adding quality of life upgrades, more deeply researching the platform, more deeply researching the feasibility of my componentry and fabrication. HOPEFULLY buy most of the drivetrain bits in advance and make sure the entire thing works on a bench, THEN start converting in spring of 2020 and be done some point before spring of 2021


This is obviously going to evolve with time, but the way forward seems relatively clear for now, minus some wait time

there's a companion thread over on the c3 forums
https://www.corvetteforum.com/forums/c3-general/4362171-corvolt-the-71-restomod-journey-to-electric.html

also there was an initial thread over there proposing the project and hashing some stuff out
https://www.diyelectriccar.com/forums/showthread.php/rate-my-build-plan-c3-corvette-201533.html
 

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I love a well-documented project.

I'm converting the little brother to your C3, a blend of 1970 and 1972 Opel GTs. Poor man's C3 I suppose.

https://www.diyelectriccar.com/forums/showthread.php/matts-1970-opel-gt-project-log-200587.html

I went over to your thread on the Corvette forum. Yep, same BS I got on my Opel GT forum. Lots of ignorance of people who have no clue about what an EV is (some deliberate and some innocent), a handful of people condemning you for what you're doing to your own property because there are correct and incorrect opinions to have about cars apparently, and a mostly supportive group of people just happy that you're passionate for project and sharing it with the world.

Your car looks fantastic. I've been looking at GTs so much, I forgot how much I love the comparatively steroided-up look to the C3's. Looks stellar and sinister in black.

There were a pair of C3 conversations happening here in the last year, seem to have fizzled out, haven't seen updates in a long time.

A few notes...

- You're avoiding the Model 3 drivetrain. Damien's already got his spinning, he usually sinks his teeth in until he's got a success. He piggybacks on Johannes' Open Inverter software, which works pretty much universally, so, once he's reverse engineered the Model 3, it's pretty much just waiting to go. It's not that many wires. It's a 6-pole (3 paired) resolver, that was his last stumbling block, and then 3 power leads. The motors are dead simple.

You don't have to use the inverter there to drive the motor. You can use any inverter, as demonstrated by him using the Prius Gen 3. This week's news about the Prius Gen 3 inverter, Damien discovered just the MG2 inverter alone will handle 500 amps before gracefully shutting down. The Gen 2 did about 70% on the MG1 as its MG2, so, you could realistically see 850 Amps out of an inverter you can often pick up for around a hundred bucks. Just ludicrous value for engineering and hardware.

- I would not use the fancy expensive controller you're planning. I think every single Tesla controller sold is based on Johannes' Open Inverter open source project, they just print and rebrand their own boards. You don't get any support beyond using the forums to help troubleshoot, but it's like 1/10th the price.

- You're worried about suspension. Why not just grab the whole suspension from the Model S or Model 3 or whatever you're going to use, and adopt it wholesale? Only issue might be width, Teslas are fat cars, but, if you want it low with wide flares, no problemo.

Sounds like you've got this all pretty well researched. I'm guessing with you having lost your job recently that this has become a bit more of a budget build, so, maybe some of those are corners you want to cut.

I was on the fence about you whittling a coffee table into a toothpick, taking a running, modded 'Vette when there's gotta be some aborted projects around for cheaper and easier. But, I like your idea of just driving it first for a year. It'll get you nice appreciation for the old, and a good comparison to what it became.

Keep us all updated, would love to see regular updates.
 

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Discussion Starter #3 (Edited)
i'd classify the opel as more like the lighter, more nimble european c3, probably a better ev candidate to be honest. It's just that i've loved the c3's design forever.
the ope GT's curb weight is 1900-2100 pounds, the c3's is over 3500!

- You're avoiding the Model 3 drivetrain.
indeed damien's been making great progress, and that may be a possibility later on, but for now i'm researching based on the model s motor in terms of mounting, most of which will carry over to the model 3 motor if i switch to that. IT also depends on if AEM supports the model 3 motor any time soon, which is probably likely? Also the power peak of the model 3 motor is unknown, while the model s motor can make 600hp without too much fuss

- I would not use the fancy expensive controller you're planning.
i'm doing everything possible to remove install complexity and points of failure, as well as remove "fiddly bits", AEM's controller is (according to people using the early pre-release versions) really polished and they have excellent customer support. You definitely pay for that in extra cost but this is one area where i'm ok paying extra to avoid headache

- You're worried about suspension. Why not just grab the whole suspension from the Model S or Model 3 or whatever you're going to use
that was my original assumption but i had a talk in person with brian from ev west at fully charged live and he basically begged me not to do that. It'd actually be far more involved to graft an entire subframe onto the c3's ladder frame, not to mention after all that work you'd have a downright mediocre suspension setup with the model s (doesn't even have much adjustment), or a kinda-ok suspension setup with the model 3. He strongly recommended sticking to the very large c3 suspension aftermarket

I was on the fence about you whittling a coffee table into a toothpick,
i wanted to avoid doing restoration work which tends to be really time consuming and not as rewarding. And yeah i wanted to actually drive the car for a while before taking it offline for months, instead of it arriving at my door already on jackstands such that i can't enjoy it.
and again, with the one year time delay, no sense getting something that'll just rot in the air
 

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probably a better ev candidate to be honest. It's just that i've loved the c3's design forever.
Agreed. I'm not a car guy, but the only car I've even really had a strong opinion on, is how much I love the C3.

I'd looked at picking one up cheap for a few years, and then considered back and forth whether it was too heavy for a cheap conversion. Then I saw a GT in a car lot when I went to buy some winter tires and I was like "Wait, that's what?"

A few months later I drove to Arizona to buy 2 of them :p

i'm doing everything possible to remove install complexity and points of failure, as well as remove "fiddly bits", AEM's controller is (according to people using the early pre-release versions) really polished and they have excellent customer support. You definitely pay for that in extra cost but this is one area where i'm ok paying extra to avoid headache
Well, one thing you could do, because the cost difference is going to be so extreme, is just buy Damien's, and if it gives you a whiff of issues, go buy AEM's. It's likely only going to cost you 10% extra.

If the cheap solution was like, 70% the cost of the supported one, well, then I could see how you have to only pick one. But, since the unsupported one is so far apart, there's hardly any risk in at least trying to make it work for you.

i wanted to avoid doing restoration work which tends to be really time consuming and not as rewarding.
I hear ya. I'm 1 year into my "summer project" last year. Without seeing a motor spin yet.
 

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Discussion Starter #5 (Edited)
is the cost difference that extreme though?

the aem VCU is $1500 for a single motor application, $1200 for a cd-7 display (new, i may find a used one for cheaper), $750 for a pdu unit for switching stuff, which i may not actually need if i keep all the stock controls for headlights and stuff and keep the entire stock 12v system....
and $300 for a usb can cable for programming....which i'll admit is rather high, i may find that used.

also i may have a way to get decent discounts on all this stuff, which changes the calculus somewhat

and damien's still be just the controller, right? i'd still have to purchase all the peripheral stuff like displays
 

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as for mounting, i was thinking this, a 180 flipped position, with three mounting arms welded to the ladder from on the front back and side
i'll need to cut into the car's fiberglass body, but i don't know how much


Is that drive unit “upside down” ? If so, Are you sure you can just flip it and run the Large Rear Drive Unit Upside down ? My concern is there is an oil pump like devise inside to lubricate the gears. If you flip the motor will it still be able to pick up the oil and properly lubricate ?

I think certain builds people install the drive unit orientation in such that to drive forward they run it in reverse. But to do that they install a modified oil pump or modify the existing to lubricate in reverse.

Any one know if flipping 180* would still allow proper gear lubrication or there is a modification of some sort available to allow it ?
 

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Discussion Starter #8 (Edited)
sure as heck hope it works when flipped 180 as thatls the only orientation that will work for this build. If i keep it in the normal orientation, it'll hang way too far out back
although that in itself is potentially a bonus to the model 3 motor, since it seems to run in that "motor forward, diff aft" configuration



Thing is, i cannot for the live of me find any model 3 CAD models. Whoever has motors aren't scanning them, and without cad it's very difficult to mock up sizing and positioning
 

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sure as heck hope it works when flipped 180 as thatls the only orientation that will work for this build. If i keep it in the normal orientation, it'll hang way too far out back
Well, the ac motor and inverter will work and it will drive the car forward and back . The issue is the gears getting properly lubricated. It’s designed so the pump picks up oils from the bottom. Flipping it upside down and the pick up tube is at the top of the motor.

Looking at the video, it seems like the pump plays an important role spraying oil at key areas on the gears ? If it can’t pick up any it won’t be able to lubricate . It would be like driving a car with no transmission oil.

If it’s too large (Width) to fit in the correct orientation, perhaps maybe removing and relocating the inverter ? This way the drive unit will be around 21.5” wide instead of 35” ....But this won’t help at all about hanging too far back that you mention.

Yes, the Model 3 is oriented from factory the way you want to install.

It’s not as helpful as having a cad but I was told the model 3 rear drive unit is approximately 25X17X15 inches.
 

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Discussion Starter #10
my problem can be best demonstrated visually

flipped around, the motor cuts right through that large crossmember in the frame.

popping the inverter off unfortunately doesn't help in this case :(

but i was hoping to upgrade the lubrication system anyway, since the stock cooling on the motor is kinda bad to begin with and thats mostly because the oil pump is gear driven based on wheel speed, instead of oil temp
 

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Discussion Starter #12
easier said than done, i believe that crossmember is a major part of holding the body of the car onto the frame...
 

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easier said than done, i believe that crossmember is a major part of holding the body of the car onto the frame...
Then move the mountings - or add a mounting frame that meets up with the body and still misses the power unit

Chassis stuff is easy! - modern MIG welders are awesome - and you can do all of your "modeling" with a couple of dollars worth of cardboard

It's much easier to mess with what is basically an incredibly simple and crude ladder chassis than to mess with a modern and sophisticated power unit

In my world (people with different skill sets will differ) it goes

Most Difficult to least Difficult
SOFTWARE
Electronics
Precision machined parts
Bodywork
Suspension
Chassis
 

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Kevin Sharpe tried to get some crowdfunding going for a 3d scan of the Model 3 motor while it was on loan at Damien's. But that mostly fizzled. Not enough people need it or are interested in it.

You'd think that EV shops would jump at that chance to pitch in, but, nope.
 

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a very big problem is going to be the rear suspension geometry, which normally relies on a leaf spring and a sway bar system bolted to the bottom of the diff, and the half shafts actually push and pull on the diff as a suspension component, VERY BAD For a tesla motor!
I'm looking into alternative suspension systems which use coilovers instead, like ridetech's, which is $1900 without the actual coilovers.




but even with this i'm not sure if the half shafts are still active suspension components?
Yes, C3 (and C2) suspension is horrible.

The leaf spring in any generation of Corvette suspension is not part of the suspension geometry - it acts only a spring, not a locating arm. The leaf spring gets replaced by coils for a few reasons
  • to change spring stiffness (easy to swap in various coils, hard to get custom leaf springs made to fit the car for different rates, especially with the later fiberglass leaf springs),
  • coils on shocks are lighter than the steel leaf spring plus shocks, and
  • mounting the leaf spring can be a problem with different final drive units (which is the case with this conversion)
... but changing the geometry is not one of them.

The RideTech system shown still uses the half shaft as the primary lateral suspension links (and the small strut rods shown as the required second lateral link per side). It just has nicer trailing arms, designed to work with their coil-over-shock and mount (which they call "MuscleBar") system.
 

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I'm converting the little brother to your C3, a blend of 1970 and 1972 Opel GTs. Poor man's C3 I suppose.
The Opel GT has the same styling (not just by coincidence), and they both have the long-hood/short-deck form and set-back engine layout that are suitable for this style of car... but that's where the similarity ends. Structurally and in rear suspension design they are wildly different, and lead to different conversion solutions.
 

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... i had a talk in person with brian from ev west at fully charged live and he basically begged me not to do that. It'd actually be far more involved to graft an entire subframe onto the c3's ladder frame, not to mention after all that work you'd have a downright mediocre suspension setup with the model s (doesn't even have much adjustment), or a kinda-ok suspension setup with the model 3. He strongly recommended sticking to the very large c3 suspension aftermarket
It is important to recognize the difficulty of adapting a subframe to the C3's frame, and the width is a critical issue, but anyone who would describe either Model S or Model 3 rear suspensions as "mediocre" or "kinda-ok" and recommend the design which GM abandoned 40 years ago instead must be a serious old 'Vette fan. The aftermarket for C3 suspension is large mostly because the C3 suspension is so undesirable.

The Model S suspension is the integral link type used by Jaguar, BMW, and Alfa Romeo. The Model 3 suspension is the five-link type used by Mercedes, Mazda (RX-8 and NC/ND Miata), BMW, and others. Yes, everything in a Tesla is copied from one of the established auto manufacturers.
 

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sure as heck hope it works when flipped 180 as thatls the only orientation that will work for this build. If i keep it in the normal orientation, it'll hang way too far out back
although that in itself is potentially a bonus to the model 3 motor, since it seems to run in that "motor forward, diff aft" configuration...
Yes, the Model 3 (and now Model Y) rear drive unit is the only current Tesla drive unit which places the motor ahead of the axle line.
 

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Discussion Starter #19 (Edited)
anyone who would describe either Model S or Model 3 rear suspensions as "mediocre" or "kinda-ok" and recommend the design which GM abandoned 40 years ago instead must be a serious old 'Vette fan. The aftermarket for C3 suspension is large mostly because the C3 suspension is so undesirable..
big emphasis on aftermarket suspension, since yeah the stock isn't good

i believe his perspective is from autocross or road racing, and that it (tesla's) is heavy luxury car suspension and not sharp sportscar suspension
he's also done a lot of conversions at this point, classic and modern, so i'm trusting his take
 

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The Opel GT has the same styling (not just by coincidence)
*nod*.

They were both born out of the 1965 Mako Shark II concept, like a common ancestor.



I love how sinister it looks. Even the C3 is friendlier and more subdued.

but that's where the similarity ends. Structurally and in rear suspension design they are wildly different, and lead to different conversion solutions.
At the time, even GM's own brands weren't even really sharing notes among themselves. Let alone GM's awkward European cousin.

The C3 is a body-on-frame, the GT isn't even just a unibody - it's a monocoque, there's no frame anywhere.

They're a tiny bit the same, absurd transverse leaf springs, C3 in the back. GT in the front. The front!

Look at this goofy hillbilly front suspension with leaf springs on a 2000lb sportscar:



I want to replace it with something more modern (from a junkyard), but I wouldn't know where to start. But I'll leave such complaints in my own thread.
 
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