DIY Electric Car Forums banner

Rate my build plan (c3 corvette)

23787 Views 80 Replies 10 Participants Last post by  MattsAwesomeStuff
5
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
See less See more
  • Like
Reactions: 1
41 - 60 of 81 Posts
... i think this detroit speed kit solves the axle shafts as suspension members problem
https://www.detroitspeed.com/1963-1...3-82-corvette-stock-differential-041740-group
....for $8,800 :eek:
Yes, DECAlink completely replaces the Corvette's rear suspension with a sound multi-link suspension that does not use the axle shafts. It uses two longitudinal links per side, similar to the stock suspension in that respect, for compatibility with the C3 structure; as a result, it doesn't need an extensive subframe. If I were upgrading a C3 and wanting to keep the structure close to stock, I think this would be a good choice... but the probability that I would ever spend tens of thousands of dollars to upgrade a C3 is zero. ;)
Tesla Model 3 suspension and drive unit

Although this is making me lean a little more towards the model 3 setup, not sure if that has better adjustment though?
At least from the top, the Model 3 rear suspension appears to be a more typical 5-link-per-side design (with steel links rather than aluminum), first popularized by the Mercedes W201 series but now widely used on vehicles with performance as a high priority.

For those trying to model suspension kinematics, these suspensions work essentially like double A-arms, with the virtual ball joints at the locations where the lines of the links intersect, somewhere within the wheel volume; the track control rod is essentially the steering tie rod.

I don't see any adjustment in the upper links in that photo, and there is the expected cam adjustment on the inboard end of the toe control link; I have no idea if there is any adjustment in the lower links, but I would guess not.

You can see the subframe, upper links, toe link, one lower link (the one with the spring and shock) and swaybar in Tesla's image from the online configurator.

Note that the Model 3 rear drive unit places the motor ahead of the axle line (just like all of the drive units for platforms designed for transverse engines, including all front-wheel-drive EVs and the Smart ForTwo ED and Mitsubishi i-MiEV). The photo linked above is taken from ahead of the drive unit and suspension; note the motor on the left of the photo (right-hand side of the car), with the gearbox to the motor's right in the photo (left-hand side of the car), inverter on the end of the gearbox, and final drive (diff) on the back side of the gearbox.

the concern is, is the 3's track actually narrower? the problem with these images is..... it's measured rotor to rotor or wheel edge to wheel edge? the c3 image measures both separately which helps
hopefully this means the rotor-to-rotor of the 3 is 62, meaning i get a free 4 inches wider in the rear which is GOOD because i actually WANT to go for a widebody setup to keep this thing on the road!
Track is the lateral distance between the centres of the tires, as shown in the C3 drawing - not the same as the hub face spacing unless the wheel/hub offset is zero. So yes, the Model 3 is narrower than the Model S and X, but still (moderately) wider than the C3. The Model 3 seems like a good match for this project in this respect - fender flares would be needed to cover the few inches of extra track plus the extra tire width (stock C3 tires were narrow by today's standards).
See less See more
hmm, double checked my cad model i have of a c3 frame
https://www.3dcontentcentral.com/download-model.aspx?catalogid=171&id=401155

i recently checked out a pretty cool race built C3 and measured the inter-frame distance right by where the gas tank sits, reads a little less than 39 inches

https://photos.app.goo.gl/G8YffM9MUTgxmBcB8

i use tinker cad as a quick an dirty alignment tool and the c3 frame seems to line up perfectly, i scaled it down by 100 to fit into tinkercad, and it's 10mm between the same two rear frame members on the model, which is pretty much exactly one one hundredth of 39, so the c3 frame is very close to accurate.

the model s subframe piece cad though, not so sure about that one. I'll download this super accurate model and cross reference
https://grabcad.com/library/tesla-rear-drive-unit-1
really wish i could embed images from google drive
anyway, the motor model is quite validated and sits just right in the subframe model so that seems accurate too

unfortunately the giant can impacts that crossmember bit, so that'll have to be cut off and a new crossmember welded up :(
https://drive.google.com/file/d/1WOz5oaK8srJ2t_ot8tWBb4p5Ygk_Get1/view?usp=sharing

another benefit of a model 3 subframe setup: the motor's quite a bit smaller
4
I did some quick measurement on the Tesla model S cradle so you could verify


Distance B ....Looks like 43.5


Distance A ....Is about 41.75


Distance C ... approx 23.625



Your also have to give some thought about your Rims. The factory rotors and calipers are large and I don't think your going to be able to use a rim smaller they the factory (19").
See less See more
Your also have to give some thought about your Rims. The factory rotors and calipers are large and I don't think your going to be able to use a rim smaller they the factory (19").
ah, thank you for the measurements
19" wheels are just too damn big for the c3, 18 is already pushing it, the model 3 can do 18s so i guess that's yet another reason to get a 3 subframe over an S :(
unfortunately the giant can impacts that crossmember bit, so that'll have to be cut off and a new crossmember welded up :(
https://drive.google.com/file/d/1WOz5oaK8srJ2t_ot8tWBb4p5Ygk_Get1/view?usp=sharing

another benefit of a model 3 subframe setup: the motor's quite a bit smaller
My guess is that crossmember is there primarily for the final drive and leaf spring carrier, so it may not need to be replaced at all.

The other obvious way to address motor bulk is to use the Tesla Model S/X small drive unit. While never used by Tesla as the only motor for a vehicle (it's only in AWD variants), and obviously less powerful than the large drive unit, it might still provide better performance than most stock C3s.

The Model 3 motor isn't just smaller - it's mounted ahead of the axle line, changing what it might run into. The Model 3 subframe is also differently shaped, due to the different suspension.


I see the name "corvolt" in an image filename. "Volt" made me think of "Bolt" - you could use the 150 kW Chevrolet Bolt motor instead of a Tesla, and not get anywhere near that crossmember. ;)
Eh, small drive unit tops out around 300. It's certainly nice, but not enough for a proper american sports car.

really wish i could get a 3d scan of a model 3 subframe/motor, but it doesn't seem to be a thing yet :/
the motor being a little forward just means it might intrude into the cabin fiberglass a little, i may need to add a hump into where the cargo area is

CorVolt as in, Volt batteries. CorBolt honestly just sounds odd, also that motor is meh.
Your also have to give some thought about your Rims. The factory rotors and calipers are large and I don't think your going to be able to use a rim smaller they the factory (19").
Good catch. This is a common issue with modern components in older vehicles. The most common solution is to just use the large-diameter wheels, even if they often look strange with the old styling.

Using the smallest wheel size for a given model may require the selection of corresponding brakes.

Overall tire diameter can be an issue, too, but the G70-15 typical of this era of Corvette isn't far off the overall diameter of the tires on a Model S or Model 3 (and is actually taller than the 18" Model 3 tire). Of course tire sizes can be changed, but that affects motor speed for a given road speed.
Eh, small drive unit tops out around 300. It's certainly nice, but not enough for a proper american sports car.
...
CorVolt as in, Volt batteries. CorBolt honestly just sounds odd, also that motor is meh.
Right, you would need either boost the Bolt or Tesla small motor output, or build a two-motor all-wheel-drive C3 (with either brand of drive units). :D

And regardless of the motor or even the battery, "CorVolt" is a pretty good name for a Corvette EV. :)
Good catch. This is a common issue with modern components in older vehicles. The most common solution is to just use the large-diameter wheels, even if they often look strange with the old styling.

Using the smallest wheel size for a given model may require the selection of corresponding brakes.

Overall tire diameter can be an issue, too, but the G70-15 typical of this era of Corvette isn't far off the overall diameter of the tires on a Model S or Model 3 (and is actually taller than the 18" Model 3 tire). Of course tire sizes can be changed, but that affects motor speed for a given road speed.
similar diameter yes, but 19s give you a noticeably worse ride. I always always opt for 18s whenever possible because they still look quite good, but you have enough sidewall to properly ride.

the very old school 15" wheels with super meaty tires looks period correct but has its own handling problems, so i have no interest in that form factor either

As for the name, i was literally planning to replace the stock lettering of "vette" with "volt", maybe add in a dash in the middle to keep the same number of letters

See less See more
similar diameter yes, but 19s give you a noticeably worse ride. I always always opt for 18s whenever possible because they still look quite good, but you have enough sidewall to properly ride.

the very old school 15" wheels with super meaty tires looks period correct but has its own handling problems, so i have no interest in that form factor either
Yes, appearance is only the start of the problems with excessive wheel diameter, or really inadequate sidewall height. Very short sidewalls are especially bad with suspension that isn't suited to them. The largest wheel / shortest sidewall combination for almost any production vehicle is not really suitable for normal street use.
Very short sidewalls are especially bad with suspension that isn't suited to them.
thankfully, 18s are well understood on c3s, they seem to work very well for good handling
19s.....much less so, wouldn't trust em
related unrelated, just shot out a few emails to a lot of the conversion shops to ask where they are in model 3 motor controller support. Polykup, zeroEV, stealthEV, HSR motors.
i know EV controls has it on their roadmap, and EV west hasn't bothered with them since the older large rear drive units and the small front drive units are fine for them for now.

apparently damien and group are doing a bit of a raffle on a motor to fund open source control board development, which is neat, and might be the only way to accelerate this
https://openinverter.org/forum/viewtopic.php?f=10&t=184&start=10

Zero EV has one taken apart but it'll take some time before they have a solution
057 technology says they're in the r&d phase for it, so it's on the horizon, but still quite a ways off
thankfully, 18s are well understood on c3s, they seem to work very well for good handling
19s.....much less so, wouldn't trust em
But if you are using Tesla suspension then you ARE using suspension that will work with the 19's!
But if you are using Tesla suspension then you ARE using suspension that will work with the 19's!
in the rear, yes, but not the front, unless i get some aftermarket suspension geometry upgrade for the fronts.
Although the front's pretty competent in general so, maybe it'll be fine with just a coilover upgrade?
sent out an email to a very highly recommended fabrication shop called chuckle's garage https://www.chucklesgarage.com/

going to try to get a very rough (plus or minus a grand) estimate on how much this might be for a shop to do....and more importantly, what i could do on my end to reduce that cost like more detailed modeling in CAD and getting CNC machined mount hardware....maybe...

The person who recommended this shop claimed that when he used to do this stuff back in 2012, suspension swaps were anywhere between $6500 and $10,000 depending on complexity.
sent out an email to a very highly recommended fabrication shop called chuckle's garage https://www.chucklesgarage.com/

going to try to get a very rough (plus or minus a grand) estimate on how much this might be for a shop to do....and more importantly, what i could do on my end to reduce that cost like more detailed modeling in CAD and getting CNC machined mount hardware....maybe...

The person who recommended this shop claimed that when he used to do this stuff back in 2012, suspension swaps were anywhere between $6500 and $10,000 depending on complexity.
I built my whole car for less than that!
Your budget is $15k plus another $20k - right?
I converted my C3 about 10 years ago. Lots of pictures at: Advanced-ev.com

  • Space for batteries isn't the big issue. If you're going to race this thing, the big issue is keeping them low in the car and between the front and rear wheels.
    • I used twenty-three lead-acid Odyssey PC1500 - 12V, 50lbs
    • Total pack weighs 1,150 lbs
    • Mounted 11 in the front and 12 in the rear - The rear was easy
    • Weight distribution:
      • Scales at a recycle center showed
      • Total weight: 3,860 lbs
      • Front: 1,880 lbs
      • Rear: 2,120 lbs

Attachments

See less See more
Your budget is $15k plus another $20k - right?
I converted my C3 about 10 years ago. Lots of pictures at: Advanced-ev.com

  • Space for batteries isn't the big issue. If you're going to race this thing, the big issue is keeping them low in the car and between the front and rear wheels.
    • I used twenty-three lead-acid Odyssey PC1500 - 12V, 50lbs
    • Total pack weighs 1,150 lbs
    • Mounted 11 in the front and 12 in the rear - The rear was easy
    • Weight distribution:
      • Scales at a recycle center showed
      • Total weight: 3,860 lbs
      • Front: 1,880 lbs
      • Rear: 2,120 lbs
oh dang i remember seeing your build multiple times, seems like the only electric c3 out there.
that warp 11 mount is quite cool
ever thought about bringing it back with modern batteries? could cut that pack weight in half for the same range, get the curb weight back to what it was stock

also, where'd you get the cad model of the frame?
41 - 60 of 81 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top