Ducati powered Fiat from California

Introduction

Hello everyone! As the title suggests, I have decided to build a Ducati powered Fiat 500!

I have restored a couple classic American cars, some motorcycles, and have designed and built a handful of Formula SAE cars in college, but I've always wanted to build my own motorcycle powered road car.

After a decade of working at one of the largest Spacecraft companies in California, I decided to take a break and try to make this dream a reality. The car needed to be simple, lightweight, relatively cheap, and older than 1975 (California smog requirements). I have a buddy that did this with an old Honda S600, and another with a Fiat 850 spider, but I wanted to do something a bit less roadster-y. Then, as the wife and I were honeymooning in Italy, I saw the answer: the old Cinquecento.

There seems to be lots of motorcycle powered 500s for hill climbing, and Z-Cars is one of the most popular swaps out there with their Suzuki Hayabusa swapped "Fiabusa" (they also make a Subaru swapped "Fubaru"), but I wanted to keep the motor air cooled (no big radiator up front) and Italian. After a bit of research, I decided to go with my favorite motorcycle engine, a Ducati 1100. The last of the big, air cooled, dry clutch L-Twins. How hilariously adorable would this car be with that noise coming out of it?

I spent a few months looking for the perfect car - something that was driveable, in decent shape, but not too nice, so I could save money up front and put it toward the swap. I ended up with a clean-ish 1974 Fiat 500 R with about 26,000 km on the clock that had been imported into the states a few years prior. The body was in pretty good shape until a strap broke towing it home resulting in a head on collision with the trailer. I minimally repaired the damaged area so I could turn the wheels full lock again, then drove it around a few months until I got the car registered.

Now that the car is legal, it's time to begin the project!

I'm looking forward to sharing the progress and hearing everyone's thoughts on the build. I have reached out to a few people individually and everyone has been extremely nice and very helpful!

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Latest updates

Front Suspension and Engine Frame update

May 23, 2024

Quick update before I break for some major CAD design work on the rear suspesion and differential mounting assembly

Front Suspension

I welded in the front cross braces and shimmed/aligned all the control arms. I'm petty happy with the setup, just need massage the pinch welds for clearance at full bump. I'm running about +/- 40mm of travel (limiting rebound but could go more) with about -1.2 deg of static camber. I haven't set up the steering yet (will likely make a separate post for that) so we'll see how bad the bump steer is with this setup. I'm really don't want to make custom front uprights, like I have to for the rear!

Engine Frame

On the last update, I had just started tacking together the engine frame, but was still missing the other half, some engine mounts, and the structure to connect the two. Well, now it's all (mostly) welded! I still need to add some gussets and clean up some of the welds, but I'm happy to move on to the next portion of the build - the differential frame. This will probably take a while to flush out, since this frame will hold the differential/reversing gearbox and the suspension (control arms, shocks). I want to make sure this all is lined up pretty well since there's not a ton of room under this thing.

Reactions: lazylobster and Bounding Bambino

Long Overdue Update!

Apr 5, 2024

It's been almost a year since my last update! A lot has been going on, but almost none of it Fiat related. I took a break from this project as we welcomed our first daughter last June. Now that we've gotten a bit into a rhythm, I've been able to give the Fiat more love!

Front Suspension

During my last updated, I was convinced that a prior repair job had resulted in an asymmetric suspension setup; however, upon further inspection, it appears that the chassis hard points are symmetric but the fenders are not. So I redesign the suspension, again, and I used this opportunity to lower the roll center, add more camber gain, and make some custom upper control arms using rod ends to give this suspension a lot of adjustment. I also now have access to a 3D printer so I was able to make some test parts to make sure I was happy with the alignment before building everything. I ended up adding adjustment to shift the wheel forward or rearward 1/4" (6mm) allowing me to better fill out the wheel well. Has anyone else felt that the front wheel should move rearward to better fill in the wheel well?

Still need to finish the cross brace supports, finalize the hardware, and probably add an anti-roll bar and a rebound stop (will just use the shocks for bump). The GAZ shocks are totally busted, leaking and not holding pressure, so that's disappointing. I might find a local shop to rebuild them (shipping back to the UK is not cheap), or look at switching to a different manufacturer. Also, it is worth noting that with this steering rack and brake upgrade, I do run into interference at full lock between the brake caliper and the upper control arm. The custom arms are designed to reduce this but it will still contact. Not sure if anyone else has run into this issue, but I'll look at modifying the rack to limit the travel so that this can't happen while driving.

Engine Frame

I ended up redesigning to engine frame, adjusting the position of the engine so I don't need a belt tensioner and modifying the frame so I have access to the engine bolts on either side of the rear panel. New parts were designed and printed to verify measurements on the engine and the Fiat's frame, then I had the tubes laser cut and routed out a tacking jig. Once I was happy with how everything fit, I welded it out and cross my fingers. It fit!

Overall, I'm pretty happy with this aesthetic of this frame and how it pays tribute to the classic Ducati trellis frames! I still need to finish welding out the frame, add the last engine mount, gusset everything, oh and build the rest of the engine frame, but this rear section, making sure everything lined up between Fiat's frame and the Ducati's engine mounts was the highest risk. Glad this all seems to fit up nicely.

Looking forward to what everyone thinks. More to come, with hopefully much less time before the next update!

Reactions: lazylobster and Bounding Bambino

Suspension Update: Part 2

Apr 10, 2023

Hey Everyone! I it's been about 3 months since my last update, and there has been some good progress, though not as much as I'd like (is it ever?). See below!

Front Suspension

Last time I realized that there had been some funky front end repair work that resulted in my suspension mounts being off. Upon further investigation, it does appear that the driver suspension points are shifted about 1/4" to the outside, when compared to the passenger. I tried to take this difference up with shimming and adjusting the control arms, but although I could get the static alignment correct, the camber changes were very different between the two sides. Also, I wasn't super happy with the design of those control arms and that they contact the support frame under full bump, SO, I've decided to make a new suspension mounting structure, lower control arms, and modify the upper control arms to fit the bigger tires with this messed up body.

I made asymmetric lower mounts to correct for the difference in mounting positions and to allow for lower and longer lower control arms, give me a better roll center height and camber control for the new wheel size. The lower structure is pretty simple, so I can remake that once I fix the suspension mounts.

Mounting the coil overs to the wheel well gave me some concern, so I built a test rig to see how much load I could put into the shock tower before yielding the structure. I got up to 800 lbF with less than .015" of deflection and decided it shouldn't be a problem keeping the stock structure as is without added re-enforcement. Also, the MrFiat coilovers didn't seem to be of the best quality and were limiting my total droop travel, so I ordered some GAZ shocks. Excited to see the difference!

I also finished up the steering, modification of the brake pedal for clearance, and added a spacer to the pedal assembly to give the master cylinder a bit more room.

Rear Chassis

I've decided to keep the front relatively mild from an upgrade perspective - using all standard off the self 126 parts and upgrades. I am making slight modifications to the control arms and mounting structure, but in general, it's in the spirit of the original car. The rear needs to be a totally different animal due to the engine packaging. This Fiat is going to be all business in the front, party in the back!

First, I cut out some of sheet metal that was going to interfere, like the rear suspension mounts, engine bay closeouts, rear engine mount and part of the air inlet snorkel thingy.

The Elite MX200 differential/reversing gearbox arrived so I built a simple jig to hold the engine and diff with respect to each other so I could put it in the car and make sure everything lined up the way I had hopped. As expected, I needed to change things around a bit to ensure I had acceptable CV angles, spacing between the engine and differential for the correct belt length, and to make sure I had good clearance to the engine lid (decided I want the option to keep the engine completely concealed)

After I was happy with the rough position of everything, it was time for another scan and to get heavy into the design work.

The frame needed to connect to the vehicle at 4 points: two forward lower swing arm mounts, and the two rear engine panel mounts. The frame not only needed to hold the engine, differential, and belt drive assembly, but it also needed to contain my suspension mounting locations, and look cool!

I started with the engine portion of the frame. With the motor being lifted from a Ducati, I wanted to retain the same "trellis" look of those bikes. I also wanted to have the option to run this car without the engine lid and panel, primarily help evacuate heat out of the engine bay during aggressive driving events, but also to look awesome. The frame is actually two parts (shown in green and red) that way the engine can actually be removed without cutting it out of the frame!

Next was to figure out the frame around the diff, and suspension pickup points. After doing some quick and dirty suspension sketches, I realized I could package a double wishbone suspension, which I used to set my nodal constraints. Then it was a matter of connecting the dots in a side/elevation view, then in bottom/top/plan view. I wanted to give the diff some adjustment since hitting the two drive axis will be extremely important, so I have incorporated slots and shims accordingly.

After I was fairly happy with that design, it was time to tie everything together, adjust, repeat! After quite a few iterations, I ended up with a design that I can make work. I've now ordered the laser jet sheet metal parts tubing so hopefully I can start fabricating next week!

In the meantime, I need to finish up the outboard suspension details (shock mounts, a-arms, uprights) and belt tensioner. That should be the main things to knock out before she can be back on her feet again!

Looking forward to hearing what everyone thinks and I promise to not let so much time go by before another update!