Ditchdigger SuperDork
12/23/13 12:43 a.m.

Some years ago I sold my '88 325is and foolishly followed my heart and drug home a total POS Fiat 850 Berlina.

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I spent a few months getting it on the road and proceeded to drive it daily for 3 years. Its 817cc motor provided a blistering 20 second to 60mph acceleration. but it managed a few different states of tune over the years. It culminated in the megasquirted, turbocharged 843cc version that it is currently. At 20psi it thrusts the car to 60 in well under 6 seconds and provides more smiles per mile than anything I have ever experienced.

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A while back a freak snowstorm hit and my carport collapsed on it. The damage was surprisingly minimal but coupled with the other ways my life fell apart at the same time I just lost the desire to get the car back up to snuff.

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But that desire is back with a vengeance! So this is to document the build and what I am changing and improving. It will also be a great place to discuss options and get the hives thoughts on things.

So first order will be repairing the roof.

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The rotisserie at work is currently free so I can do all of the body repairs. Flaring the arches to fit non staggered tires will be a must. I am running 165/45-15's up front and 195/45-15's in the rear currently and would like 195's all around.

Graefin10 SuperDork
12/23/13 4:56 a.m.

The first time I saw that car pop up on reader's rides I fell in love with it. It made me sick to see that it was damaged. I'm glad to hear that you didn't give up on it and look forward to see it's latest mods.

fanfoy HalfDork
12/23/13 8:31 a.m.

Yeah! One of my favorite reader's ride back with a vengeance. Looking forward to your progress.

chandlerGTi SuperDork
12/23/13 8:35 a.m.

Yes, glad to see its return!

Woody MegaDork
12/23/13 9:12 a.m.

I love everything about this, aside from the collapsed carport!

Ransom UberDork
12/23/13 9:29 a.m.


Ditchdigger SuperDork
12/23/13 11:07 a.m.

My christmas bonus this year from my boss consisted of a Garrett turbo from a new 500 Abarth

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And a set of 66mm Forged Borgo pistons

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This means that I am building up my old 903cc block into a stonkin' huge 931cc monster!! The larger turbo should help too. I currently have a TD03 from a Volvo S80 on there and it is proving to be too small.

Mr_Estrotica Reader
12/23/13 11:21 a.m.

Awesome! I'm glad to see it's getting the love it deserves!

mblommel Reader
12/23/13 11:28 a.m.

In reply to Ditchdigger:


So glad to see this one back on the radar. Best of luck and please keep us updated!

bgkast Dork
12/23/13 12:40 p.m.

I think mblommel summed it up.

Ditchdigger SuperDork
12/23/13 2:33 p.m.

One of the main reasons I started the build thread early was to spitball some transmission ideas.With 4.63 gears and a 0.96 4th it turns 5200RPM at 70mph. Throwing more horsepower at the car will do nothing to make it any more liveable.

I was all prepared to start a discussion about modding a Porsche 924 transaxle with a 915 ring and pinion and building the new motor up to turn backwards, IE clockwise.

This morning "Dave the gear man" came into my work and since I had audience with him I chose to pick his brain a bit. Dave is a mechanical engineer who went to work for Hewland transmissions out of college in the 60's and later went to work in NASCAR doing gearbox and diff setup for Earnharts team. Since then he is the local go to guy for diff and LSD setup.

An idea I have had for years (and brought it up here a few times) is taking a FWD Audi trans and flipping it around to the rear of the car . That would give me 5 reverse gears and 1 forward. But the 850 lump spins CCW so I would have 5 fully synchronized forward gears. I worried about the ramifications of working a transaxle backwards and never did it.

Dave set my mind at ease. Everything will work fine. All the gears and synchros don't care and the ring and pinion will actually be a bit stronger running on the coast side. They will be noisier though.

Great news! I already own an Audi 4000s trans. A Honda flywheel and pressure plate will provide function in the CCW direction and work with the Audi clutch disc.

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Man! Everything is coming up Millhouse this week.

SyntheticBlinkerFluid PowerDork
12/23/13 10:36 p.m.

Awesome to see you back working on it again.

Kenny_McCormic UltraDork
12/23/13 11:22 p.m.

Wait, won't spinning a helical gear set backwards reverse the direction of the thrust forces?

Ditchdigger SuperDork
12/23/13 11:27 p.m.

Me too!

So back when I started throwing around the idea of using an Audi transaxle a gent named Gabi with the help of some iffy translation software got the idea that I had already done the swap. In the grassroots way that seems to only exist in places like eastern Europe he "followed my lead" and did the swap using a VW polo flywheel, clutch and pressure plate and contacted me a year later to see if mine was working as well as his was.

Here are the pics he sent me.

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His issues pretty much were just that the stock shift linkage resulted in a backwards pattern. I need to look into solutions for that.

If he could do it with little more than an angle grinder, drill and what looks to be the tool marks from a rock and sharpened stick (Gabi if you are reading this I am just joking, I totally respect and am in awe of what you did!) I can do almost as well with friends with CNC plasma cutters, my lathe and borrowed time on knee mills.

Now for the fore and aft movement of the shifter I think I have a solution.

The 850 shifter has the fulcrum above the linkage

But a Fiat 600 shifter happens to have the fulcrum at the bottom and the linkage up higher

I am a little stuck on reversing the side to side motions. If I can't figure that out I still have a cable shifter setup on the garage wall that I will try to fit much like the VW dune buggies use.

Ditchdigger SuperDork
12/23/13 11:28 p.m.
Kenny_McCormic wrote: Wait, won't spinning a helical gear set backwards reverse the direction of the thrust forces?

Yep. But there are thrust bearings on both sides of these gear boxes.

Kenny_McCormic UltraDork
12/24/13 12:00 a.m.

:facepalm: of course there would be, or else it would grenade under engine braking.

AngryCorvair PowerDork
12/26/13 2:31 p.m.

Ditchdigger, i'm glad to see this car being resurrected. very cool.

Kenny, don't ever feel ashamed of not having all the answers all at once. just asking the question shows you've got your thinking cap on, and are far ahead of a lot of the mouth-breathers out there in the world. :-)

crankwalk HalfDork
12/26/13 7:57 p.m.

Super cool! Good luck with it.

Kenny_McCormic UltraDork
12/27/13 1:41 a.m.

In reply to AngryCorvair:

I'm well aware of it, its all the people around me who keep calling me smart.

Knurled PowerDork
12/28/13 8:05 a.m.
Kenny_McCormic wrote: :facepalm: of course there would be, or else it would grenade under engine braking.

But engine braking is never as much force as the engine can provide.

That said, the 4000S transaxle is more than likely more stout than you'll need. More stout than you can fit clutch, anyway. One local-ish guy found that once you figure out the clutch problem, 300+hp is enough to break gears at will. (roll into power - trans goes boom) That's in the forward direction.

But you have half the displacement so you should be good to go.

For the shifter, I wonder if you can take a shifter box off of a RX-7/Miata trans. They reverse the "rotation" of the shift knob as well as the direction of throw. The problem is that the shift rod isn't located by the shifter box, it's located by the transmission.

Boxy02 New Reader
9/30/16 12:05 a.m.

Great build! I know this is an ancient post, but...any progress? Interested in the implementation of the Audi gearbox and your upgraded turbo motor, thx!

BrokenYugo UltimaDork
9/30/16 1:48 p.m.


Boxy02 New Reader
9/30/16 3:58 p.m.
BrokenYugo wrote: https://grassrootsmotorsports.com/forum/build-projects-and-project-cars/71-fiat-850-sedan-the-redux/100510/page1/

Muchos gracias!

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