Alfa V6 into 73 Spider

[adelspyder]

Well, the good news is that after a few false starts, my brother and I managed to source an Alfa Sei diff. The not so good news is that of the 2 differentials located, the best gear set that we could source was the 4.27 ratio (his preference is the 3.62 or 3.83 ratio), but he has some ideas to adapt a different crown and pinion set that may get him around this problem.

So with the diff in transit to Australia, he was able to source a local v6 75/Milano deDion setup (complete with stronger v6 CV joints and the Watts link rear end), carefully measured the required reduction in track and length required, and has just picked up the tack-welded unit from the engineer tonight to test fit on the car.

I just got around helping him - it’s looking great!

Here are some photos of the deDion unit and the trial install. Clearance around the petrol tank seems be close, but okay (wait until the Watts link is installed!), and the front of the deDion triangle lines up just behind the rear of the floorpan, so no sheet metal mods required here.

Some more trial fitting will occur soon, so I’ll try and get some better photos up shortly.

We are still trying to chase up the upper diff mounting beam from an Alfa Sei to help with mounting the differential, and an Alfa Sei gear set (either auto 3.62 / diesel 3.83) so if anyone has any leads…….heeeelp!

To those who helped with leads in sourcing the diff, thanks so much.

[Hamish]

Most impressive conversion, very well thought out & engineered, and that's just the engine swap! And then you go and decide to fit a de-dion rear end as well

Interesting to see how well the de-dion fits under the back of a 105, I would have thought 'stuff' would be in the way, and a lot more sheetmetal would have to be modified.

One question though, if you were starting from scratch again with the intent of changing the rear suspension from the outset, would it be easier just to fit the entire transaxle setup, even though I'm sure that would require body mods around the rear floorpan, rather than designing & casting up a new bellhousing etc to bolt up the original gearbox? I'm sure what you are doing now will work just fine, just thinking 'benefit of hindsight'

[adelspyder]

Hamish,

I'll try and get some more rear suspension photos out next week, as my brother and I will dummy trial everything in the rear end - BUT if all goes according to plan, you'll be in for a surprise. The plan is to keep as many standard body mounting points as possible, and modify the mounts on the deDion.

Good questions on the drivetrain layout – I remember playing “Devils Advocate” to my brother when he first planned the conversion, just to make sure that he was thinking through all the options while planning the project.

Initially, his thinking was to drop in a 24V V6 into the Spider, but trying to find an engine from a salvage yard here in Australia wouldn’t be easy. Therefore, he broke the project down into two stages:

Stage I: Putting the 12V engine bay, keeping the standard gearbox and differential

Hopefully, in the next few years as some of the late 90’s – early 2000 cars become available, Stage II could swing into action:

Stage II: Putting in the 24V (say, a 3.2+L ….), then modifying the rear suspension setup to the Alfa Sei deDion (and installing a Getrag box if the Alfa box proved unsuitable).

Ah well, the way the project is progressing, you’re looking at Stage I and a half (his thinking was that if he had to go through engineering certification, he might as well get the whole thing inspected and approved)!

I also asked early on whether he should replicate the drivetrain setup of a GTV6 / Milano early on, but his thoughts were simply that if he made the standard drivetrain fit the sheetmetal (body), he’d have a transmission tunnel where there wasn’t one up front, and he would have to modify the floorpan for the rear for the gearbox. And even then, he’d still have to shorten the deDion to get the track right, and modify the chassis to make it all fit. Up front, while he wouldn’t have to make a sump or bellhousing, he’d have to modify the cross member to fit the stock V6 sump, and some of the inner guard and/or rear firewall to get the exhaust to fit.

So, you have a dilemma – make the sheetmetal fit the standard V6 Milano / GTV6 drivetrain, or modify some critical components (bellhousing, drivetrain) to fit the Spider sheetmetal?

As the car has to be inspected and approved by the authorities, the latter was the easier option, as any modifications of the bodyshell would be critically reviewed. The other advantage of this option was that, if the car ever got involved in an accident, it would be easier to replace standard panels and components, rather than modified guards, cross members or floorpans.

So, with the benefit of hindsight, would he have done anything differently? Yup – should have heavily rear-ended a 147GTA, and setup Stage II right from the start!

[Hamish]

I'm very curious to see how this turns out.

[adelspyder]

Here are some photos of the initial Alfa Sei de Dion layout, and some dummying up of the Alfa Sei diff onto the Milano/75 dedion which may be of interest to some.

While I can’t confirm whether the Sei / 75 de Dion tube is the same, there do seem to be some surprising similarities:

• springs seem to be in a similar location

• shock absorbers also seem to mount in a similar location

• the front mounting beam holding the de Dion assembly seems to look the same; and

• the front of the diff (snout) also seems to perfectly fall into place on top of the front mounting beam

Just out of curiosity, the entire diff weighs around 60kgs, with the cast iron snout alone weighing in at 28kgs (ouch!). Whilst my brother and I could only guess why Alfa would make such a paperweight (as it was on a luxury sedan, quite possibly it was to reduce NVH characteristics?), the diff snout has to go as its length interferes with the floorpan.

The last photo shows the snout removed, with the rear discs and calipers (Alfa Sei discs, and would you believe some cheap NOS Alfasud calipers complete with handbrake assembly bolted right up!)

Thanks to everyone for looking and your PM’s of support – hope this adds to the Alfa knowledge database.

Dino

PS: Still seeking that elusive Alfa Sei upper mounting beam for the diff, and ANY knowledge of 3.5~3.6 diff gears that may fit!

[Hamish]

That's interesting, it looks like the snout is there to fill in the gap that would normally be filled by the transaxle, & they probably did it in iron because it was cheap. I'm guessing this would be to let them use as much existing mounting hardware as possible.

Given that you cast up an entire new bellhousing, a new 'short snout' should be do-able.

Looking at your pics, it looks as though you could make a de-dion kit that isn't much more work to fit than some of the live axle panhard rod/watts linkage conversions.

Just out of curiosity, I'm going to have a look under the bum of my GTV & see how much metal would have to be cut to fit an entire transaxle.

Very Cool!

[geofd]

Great project, really looking forward to watching this project move forward - some nice idea's.
If the kit comes to fruition I would be very interested as I have an un registered Alfa 90 with all the bits (I am sure the transaxle could be modified so it was only a diff, just like the sei diff). And would love to have a 105 GTV with the torque of the 6cylinder and most of all the noise of the 6 cylinder engine.

[hughqv]

Hey! cool project, im really curious what on earth is the sei diff out of? Does this diff have a torque tube like a 275 GTB Ferrari? Or those V8 Porsche's I forget the names of them. Real cool

[adelspyder]

Hugh,

Regarding the Sei diff, all of the research that both my brother and I have done seem to indicate that this was a unique diff only for the Sei - the housing, crown and pinion gears seem unique to Alfa, while other internals seem to be ZF-sourced.

As for the torque tube setup (this one had me scurrying for wikipedia), I don't think the Sei was this advanced, but I'd love to see some images of what a torque tube setup actually looks like.

Dino

[adelspyder]

Hi everyone,

Being the middle of winter here in Adelaide, working in a cold garage on a concrete floor isn’t the best working environment. Therefore this month turned into a planning month, focusing on tracking down key parts and the engineering required for installing the dedion and Alfa Sei differential.

Regarding the diff gears for the Alfa Sei rear end, my brother and I took a “divide and conquer” route, whereby:
• I was going to perform a worldwide search, emailing people / companies to locate new or secondhand diff gears; and
• Mark was going to research crown and pinion gear sizing from several different catalogues to find the “least mods / best fit scenario”, and then adapt to match

As luck would have it, today we took delivery of a NOS 3.61 ratio crown & pinion!

Mark is in the process of dummying everything into the rear end, and has done some trial fabrication for a main beam that will mount the diff to the chassis. He’s also had a chassis engineer over to help design the rear end, focusing on suspension layout and chassis strengthening (as well as leaving enough space to fit the watts link & exhaust).

On the front end:
• the bottom of the 2L sump has been cut off, with early dummying up of the pan under the V6 indicating it should have the same ground clearance as standard.
• still waiting for adapter plates to be made to bolt the 75/Milano calipers to the front uprights (new hubs and discs are ready, but the engineer has these and the front uprights to ensure that everything fits properly).

Thanks for looking, and I promise more photos when he has made some progress.

Dino

[Trav]

Cool project, nice work. What are the advantages of installing the Sei diff over a simpler conversion of the stock diff to watts link or panhard bar?
I don't get the design behind the Sei, it looks like they took a independent rear and turned it into a solid axle? Would someone please explain why or what I am missing?

Thx

[Subtle]

The diff is independent and the Dedion beam locates the wheels such that camber changes are minimized.

[adelspyder]

Trav,

The major advantage with the conversion to the Sei’s de Dion rear suspension is the reduction of the unsprung mass (ie. taking the weight of the differential, calipers and discs from the standard live axle suspension, and adding it to the overall “sprung” weight of the car).

If you’re ever had a RWD car bogged, you’ll know that adding weight to the back of the car helps you to gain traction – just imagine taking the diff weight off from the live axle and adding it to the body (switching unsprung weight to sprung weight), and you have the same principal (except that you’re not really adding weight, you’re transferring it from the suspension to the body).

Anyway, here are some links that probably explain it better than I do:
http://en.wikipedia.org/wiki/Unsprung_weight
http://victorylibrary.com/mopar/sprung-c.htm

So in summary, the added benefits of the de Dion rear end are:
• traction (while the watts link & panhard rod improve handling, they don’t improve straight line traction)
• improved ride quality, due to the reduction in unsprung mass

Dino

[Trav]

Thanks, I get it now. I'm guessing the de Dion tube is a lighter way to locate the wheels than a couple of A-arms on each side?


Thx

[darth dino]

Quote:

Originally Posted by hughqv im really curious what on earth is the sei diff out of?