After I found these unconventional chassis swaps with classic air-cooled bodies on modern, front-wheel-drive subcompact cars, I decided this is what I need to do too. In general, people are cutting the tops off of Priuses and stuff, leaving only a flat unibody with all the running gear, and putting old car bodies on top. Not engineering a whole new vehicle, just replacing one vehicle's body, everything above the floorpans, with another car's body.
So I bought a '73 Super Beetle.
I've always wanted a Beetle and now I finally have one. I also looked at a '66 Chevy C10 truck that would be much much easier to hide a fwd car/suv chassis under, but it was far too rotten and wrecked up. And I though that the Beetle would be better because the body "shell" just lifts up off of a flat chassis+floorpan.
The bug's paint job is only a year old so I'm sure that the rust will start coming through it in the next year or two, but the body is mostly straight. It does actually run and drive but the engine needs to be tuned up at least, or rebuilt possibly. I haven't check compression or anything since I don't plan on using it, but it does not run well at all and has a real hard time starting. Hardly any of the electronics work, it smells like gasoline real bad while driving it, you can see the ground from inside the cab, the seats are terrible, the interior in general is in pretty bad shape, etc. That transmission is the worst part though, I have the hardest time finding 2nd gear and I can't downshift into 1st gear. The previous owner did however upgrade the front brakes to disc (still manual brakes) and the steering and suspension feels really good to be honest.
The thing is a death trap and I cannot wait to retro fit it to a newer car.
After taking lots of measurements of the SuperB and my wife's 2013 Toyota Yaris, my subcompact FWD car of choice, I learned that it will not fit under the bug's body. The area of contention is the Yaris's macpherson strut towers. They're 4" too tall to fit under th bug's fenders and 10" too wide to fit between the front quarter panels and under the "hood." After thinking about it for a while, I couldn't come up with a reasonable work-around that didn't ruin the Yaris's suspension.
So it will have to be a Miata chassis.
The Beetle's wheelbase is 6" longer which is fairly significant. The Miata's parking brake cable, brake lines, driveshaft, exhaust and PPF will all have to be extended. A machine shop should be able to help me with the driveshaft, the brake lines and parking brake cable should be pretty easy to do myself, but the PPF will be interesting. It's short for Power Plant Frame, an aluminum truss that connects the rear suframe to the transmission to reduce rotational torque of the driveshaft, and may also support the tranny like a crossmember for all I know. I may have to learn how to weld aluminum! Or just bolt some steel to it.
There's two ways I can stretch the Miata's wheelbase, I think. I could cut the body in between the front and rear wheels, pull it apart, and add in new metal - like what this guy did. Or I could unbolt the rear subframe from the body, weld in some rectangular steel tube to extend the "frame" rails and drill holes 6" back, make new pockets for the rear struts, and bolt it back in. The last option seems the most elegant solution to me, but I'll probably do which ever is easier. And I can't image it will be harder to cut the width of the floorplan between the door sills and add new material.
Here's the miata rear subframe, which can be unbolted from the body I think:
Here's the Beetle's floorpan overlayed on top of the Miata's:
So it will be a little like fitting a 3d jiggsaw puzzle together. The Miata, although it's one of the narrowest car's ever built, is still too side at the door. So the door sills will need to be chopped off and they're basically what is holding the car together. So they'll need to be replaced with some beefy rectangular steel tubbing, and the bug body will bolt or weld to that tubing.
Or I could remove ALL the Miata sheet metal, leaving only the running gear sans-chassis. Then I could use the bug chassis and build attachment points for the front and rear subframes. That actually seems doable. Not sure which would be more work to be honest...
Of course the bug chassis's main structural thing is the tube going down the center, and that would be far too small to go over the Miata transmission and driveshaft. So, more fabricating. And would need to build mounts for the control arms and struts. A lot more fabricating. So, nah, this wouldn't be less work than cutting it down to this:
The above image is from Urchfab's youtube channel, where right now he's building a Ford 100E with a Miata chassis. This is a Miata NB, not the first generation NA.
He's not the only crazy guy to try this. I found several Beetle+Miatas on Instagram. Here's one of my favorites, and you can see that he cut the miata door sills off:
He didn't bother to stretch the Miata wheelbase though. It's also a standard beetle and not a Super Beetle which is a bit wider than standard.
I don't really like the tiny tires, I'll use the 25" tires on my Beetle now (which are brand new) and find some steel rims that fit the Miata's 4x100 lug bolt pattern. The larger tires might require re-gearing the Miata rear differential though. What's cheaper, new tires or diff gears?
Here's another one, a little too low for me (clearly it's a track car) but shows how the front double-wishbone suspension fits between the quarter panels (or not, when it's dropped this low). I don't know if it's a Super Beetle or not but it's probably not.
Challenges:
- The Miata seating height is so much lower to the ground that the steering wheel position will be all wrong, but the Miata steering wheel is not adjustable. Or I could use Miata seats but I wouldn't be able to see over the Beetle's hood.
- Miata's are older vehicles now. Not really getting the modern reliability and comfort that I had in mind, but it's still a huge upgrade over the bug's running gear.
- How will I bolt the bug body to the miata chassis? How will I determine how high it needs to be?
- heat and a/c vents (if AC works)
- can the radiator fit in front of the engine? Or will I have to relocate it to the rear?
- will I use the miata dash or make a custom one?
- windshield wiper motors
- airbags and crash sensors
- seatbelts
- door locks - do I need the VW key to unlock the doors and the Mazda key to use the ignition?
- will the front sway bar need to be removed? hopefully not
Steps:
- strip the miata
- lengthen the miata wheelbase
- lift the bug body up off the frame and support it up on A-arms or something
- roll the miata chassis under it
- lower it down for it's first fitment test
- measure for the body mounts, see what needs to be cut, make stuff up as I go along
- lift the body back up
- weld on the body mounts, cut what needs to be cut, etc
- drop the bug body back down and bolt/weld it to the new body mounts
- cover any gaps with sheetmetal, i.e. kickpanels, firewall, etc.
- wiring, dashboard, seats, stearing column, ec.
Before I do anything to the Beetle, I'll get the Miata running and driving well, stretch the wheelbase to match the Beetle's, and then get it running and driving again after the wheelbase stretch operation. That way I don't ruin a perfectly good Beetle in case it doesn't work out. If and when I get the whole Miata-Beetle thing running, I'll probably paint it a color I can not hate.
I'm looking at a '92 Miata MX-5 NA on Friday. The body and interior are pretty ugly, it doesn't come with a title, the rims are ugly as sin, the tires are bald, the parking brake doesn't work, and the engine idles rough and supposedly there is a vacuum leak that prevents it from running because it causes it to run too rich. I'm skeptical about buying a car I can't test drive but he's asking only $600. It's sketchy for sure but the good is that the transmission was rebuilt recently with a new clutch, and the brakes and steering (manual) are all good he says. We'll see. Maybe I can get it running before I buy it.
Update: I did it!
I ended up using a 1967 VW Squareback. I put the whole thing on youtube, here is the video of the entire project from the very start to the finished product: