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Rate my build plan (c3 corvette)

23836 Views 80 Replies 10 Participants Last post by  MattsAwesomeStuff
Location: San francisco, CA

Budget: Like 15k for the donor car, and hopefully less than 20k for all the conversion parts and any labor costs.

Donor car: 1975 c3 corvette. They're cheap, easy to convert the bumpers back to the wonderful 68-72 chrome bumper design, and have some decent safety equipment upgrades over the early cars. A clean 1975 is like 15k, a clean 1970 is 25k or more, YIKES

also, maybe some race car flair to it, need big rear tires to hold all that torque eh?

Motor: Tesla model S P85 large rear drive unit OR Tesla model 3 performance rear drive unit. The entire tesla rear subframe and all the suspension components, fabricating mounts so it bolts onto the c3 ladder frame. 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 the T-1C supports it.

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 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

Cooling: unsure yet, but the water pump and electrically controller 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: EV Controls T-1C, pretty close to turn-key, i'd buy it from EV west specifically so i can lean on them for tech support and general info. This controller's already been used in a few tesla motor/chevy volt battery builds

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.

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 50kw 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). For 50kw, maybe just stack 5 of those 10kw tesla chargers...?

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.

Timeline: purchase the c3 within a few months, 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 fall of 2020 and be done some point before fall of 2021

So, what am i missing, what bad assumptions or assessments am i making, etc
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I like your approach to research and detail. Please keep posting here to show off your progress.

I've always wanted a C3 Vette, and I've liked the idea of doing an EV conversion of one for years. But instead I cheaped out and went with a poor man's Vette, the Opel GT. (If you're curious, thread here: ). I'll be watching your build vicariously as the higher-budget higher-class upgrade I kinda wanted to do instead.


I think it's prudent to not be overly prescriptive of what you necessarily want, unless you're passionate about certain build details. Rather, figure what you want for performance, and then fill back on the stuff that can make that happen. You might be doing that, I'm not sure, just a general warning that you don't put the cart before the horse because maybe you'd be happier doing things a different way.

Donor: Love it.

Budget: $35k is enough to give you some options.

Motor: I have a feeling you're kind of set on something this powerful, or that you'd rather not bother. So, that's cool, you can make this work and your layout seems to work for the powertrain. Budget will be eaten significantly, but, it's a good foundation for the rest of the build.

Batteries: You're going with the most expensive drivetrain, and the cheapest batteries. There is nothing wrong with Volt batteries, except that they're overbuilt. That is, they are bulky and heavy for their energy density. That's going to hurt performance and range. They are cheap though. It's really the only other way to keep your budget down though, as it's usually the single most expensive component.

You're better off with Volt packs than, say, Leaf packs. But unless you're finding something less popular, Volt and Tesla are kind of the two options for you, and you might not be able to afford Tesla.

Battery prices for salvaged OEM packs may continue to fall in the future, so, if you're planning on being done in 2 years, you might want to hold off and just make the purchase later. Some of us (me, I think) kinda talked too much about how great Volt packs are for off-grid storage and their prices are double what they were a year ago, but generally I think other packs should become cheaper. You could even design for a specific form factor and just make the purchase last minute.

Cooling: Generally cooling is nearly a non-issue, and can be solved by just about anything. A half-assed plan is fine, you'll just "do something" when the time is right, and it'll take a bit longer than you hoped, but, not a lot to worry about.

Controller: The drive unit for the tesla comes with a controller of sorts. You might as well use it rather than spend $3500 on another controller. I think Damien ( has a kit you can build yourself that can control Tesla drivetrains.

Contactor: Anything, solve it when you solve it.

Power steering: Re-using one but electrically powering the hydraulics is fine.

A/C: You could just plumb one from another EV, but, it's not essential to the car working, so, maybe plan for it space-wise but otherwise upgrade it when you want it.

Charger: You might have to scale back your expectations on how fast you can charge on the road.

Safety: Safety line is a good idea. Your battery pack fuses, sure.
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drivetrain wise, i'm going for the model S rear + 34kw volt batteries because it's been proving in multiple projects by now, i really like things that have been done before because it becomes a solved problem with fewer unknowns.
From an outsider's perspective... there are complicated parts of an EV build, and there are simple parts of an EV build. When you absorb it all at once, it all seems equally complicated. So I understand your "go with a known working solution" approach.

However, just so you can make an informed decision... Controllers and motors are agnostic about where the voltage comes from. So while you might be thinking "I want batteries I know will work with X", and intimidated from leaving this known pairing of motor and batteries, that's largely an unfounded fear.

Volt batteries are pretty high power density, but other than that, any battery system you choose would work fine with the Tesla motor. There's really no matching concerns at all. If you wanted to choose a different battery pack, everything will be fine and not additionally complicated. (Also, Tesla batteries for sure were designed for use with Tesla motors :p, if you want "proven" solutions then this is proven several orders of magnitude more ).

That means range isn't important, lower weight is a priority
So, that's a huge tradeoff right there.

If lower weight is a priority, then lose range.

If lower weight is a priority, then don't use Volt packs because they are very bulky and heavy for their energy capacity. You could get much lower weight for the same range (like, double) by switching to a different battery.

and being able to push tons of amps consistently is important. Volt packs sort of fall out naturally from those requirements.
Not really. Volt packs have awesome power capacity, but terrible energy capacity.

As for the tesla motor, i just find it'd be more livable vs the old school warp DC builds, also more aftermarket support both now and in the future.
Tesla motors are definitely more awesome than some old DC motor. Regen available, more power, etc. No argument there.

But I'm not sure what aftermarket support you're thinking should/could exist for a DC motor, to ever weigh into your decisions. I.E. What or why would you ever need for support? Change the bearings ever 15 years maybe? They'll be $10 each from any store, standardized for decades. Want it to go faster? Give it more voltage. They're as simple as soup.

I think this is another place your evenly-spread fear of "support" is misplaced.

There's a reason EV west is changing some of their kits over to a tesla small drive unit architecture instead of the siemens motors.
Cost is probably the reason. Marketing is probably another. People want stuff with Tesla parts in it. There will be enough crashed, pre-engineered Teslas to supply EV West for as much business as they'll ever have. Certainly more than some system they're patching together themselves in low quantities.

Model 3 motor would be better but...well....nobody is supporting that yet, and even if they supported it a year from now it'll be a while before it's proven.
Damien just got offered a Model 3 front and rear (they're different) motor on consignment basis that some of his community is trying to crowdfund to pay for. And a few other options. But you're correct. Volunteer open-source controllers are probably the most-abandoned and slowest-progressing facet of DIY EVs. Too highly specialized knowledge required, too huge of commitments to make.

And wiring up 37kw of tesla packs in order to get 350-400v nominal, that's a lot of S and not a lot of P, voltage saaaaaaag
I get where you're coming from, but, when you apples-to-apples it, I don't think that's how it works out. There's no free lunch.

Watts per pound or watts per KWh are going to be fairly comparable. You'll avoid voltage sag by increasing the size of the pack, sure, but keeping the pack size the same? Now it's just down to chemistry. Volt packs are from a hybrid so they're optimized to be a little more power heavy, but they're also old tech and twice the weight.


Anyway, it's your project, just trying to help make sure you're making the right choices for you for the right reasons.
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For a given voltage, "tons of amps" means "tons of power": this with "range isn't important" is a description of a need for high power, not high energy capacity.
Right. But, is range that much of a non-issue?

Is the Volt actually the most power-dense option per pound?

Like, people rave about how they're power-dense per KWh (size of a pack), but, how much of that is just because it's actually pretty crappy in terms of KWh? Meaning you grab a pack of similar KWh, it compares favorably, but compare it to a pack of similar weight, it does not.

I haven't looked up the chart in a long time. I didn't think they were actually all that great.
Just FYI:

You two should watch each other's threads. You're solving the same problems on the same vehicle.
There's some weird rule about not being able to send or receive PMs until you have a certain number of posts, I think.
but man, i could really use a two car garage to have work bench space and work space!
My car is 2/3 the size of yours, and I have filled a 2-car garage, with lots of shelving to boot. I'm amazed at how much space a car is when taken apart, and when you're working on different parts of it at the same time. It wasn't something I gave much thought to, but I've been completely wrong about it.

I almost planned on working in a 10x15 storage unit originally. Which is like, 1/3 the size. Barely enough to fit the vehicle, and I thought "This'll be enough room, how much more could I need?" A lot more, apparently.
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