Race Engine Forum UK

Progress update...

The pictures should be self explanatory.

Miro

You probably have it in hand Miro but I strongly recommend you get all those old lower suspension arms shot-blasted and crack tested before final assembly. Whatever the result of that it would be wise to have a competent welder go over them and fillet/reinforce some or all of the joints esp where the rubber mounts are. I had a fracture there on my 124CSA which makes driving rather, 'interesting' to say the least...

G

Guy

You will be be surprised - the arms and axis I have mounted were never used !

We have inspected them all right and they proved to be brand new. The axis are and CV joints are also brand new !!.
There are two spare sets of arms ( used ) and one set of used axis assemblies. They will be kept for spares.

Anyway all elements we install are carefully inspected inspected, than dry fit onto the chassis and finally they will be taken off sandblasted and powder painted and than undergo final installation.

Now more updates .

The diff. It was checked out and all seals were replaced. The LSD is set at 40% , and the ratio is 7/43 ( 6.14 ! ),,.

The diff housing was previously cracked and repaired in 1980 (repair markings and signature of the welder inside the diff housing). This is the later type with modified bottom ( solid 6 mm steel plate with a front part bent upwards to slide over any obstacle rather than hit it.) My dff expert says it is in perfect shape and requires no part replacement ).
One thing: I am not sure of is what oil should be used in it given the LSD. I want to use Motul diff oil with molybdenum additive , but I am not sure this is good for LSD difs. Anybody knows ?

The flange on the diff is an exact match to my shaft - so we will not have to change any of this. I was told the shaft will have to be shortened , but this is easy . Got two old mechanics that do that .
I am still amazed that the all of Abarth suspension is parasitically a starlight fit except for diff "hanger" and support structure for reaction rods and rear arms mounting ( the easy ones).
The strut inserts issue -resolved thanks to my Bilstein expert !!

When we have originally put Bilstains adjustable fronts and Bilstein non adjustable rears we have taken a new H&R front spring and moved the original stiffer front springs to the rear ( cut off 1,5 coil ) and it worked out fine . Now I need help ....


My front Bilsteins work just fine and I have no technical reason to replace them.
I also have modern Koni struts and springs for the rear which were never tested but were made by a guy for his replica and he assures me they will work fine as well.
But I am an originality freak and want to make this as original as possible if i only can.
I want to move to original front hubs, use the original housings /inserts ( 50mm) I have for the front and the housings with new Bilstein inserts ( 45mm) for the rear. All housing inserts problems are resolved.

I am am however having a problem with the springs:

Both rear and front springs have a large ( odl style) internal diameter. In addition the front strut housings have grease nipple on its side effectively forcing the large spring diameter. ( We estimate that that safest would be 100mm inside diameter of the spring . The rear can probably accept smaller diamer-ter spring , but not less than 70-80 mm.
I actually would like to have the rear aof big diameter as in the original ( does anybody know the exact Stradale/Corsa rear and front spring diameters ?

My knowledge of the springs is marginal. I have dug up Original 131 Abarth Stradale data on the springs. They should be:

FRONT
Fiat (Abarth) part number: 4335641
Height of spring under load of 3156 + / - 127 N (322 + /- 13 kG) = 270 mm
Minimum load to compress it to the height of 194 mm = 4459 N (455kG)


REAR
Fiat (Abarth) part number: 4151719
Height spring under a load of 2793 +/- 127 N (285 +/- 13 kG) = 310 mm
Minimum load for the height of 232 mm = 4067 N (415kG)


The problem is that current most current catalogs list them either by application ( no use ) or by uncompressed length and diameter rate in (N/mm) and weight. This is totally useless, or at least not easily translatable.

Does anyone know how to translate the original Fiat data or what springs cane be used (modified as replacement for 131 Abarth).

Does anybody know what Fiat springs could be used modified to fit ?

Miro

Hi Miro

from you data you can calculate the spring rates:

A force of 4459-3156 (N) compresses the spring by 270-194 (mm)
1303 / 76 N/mm
17 N/mm
uncompressed lenth guessed 450 mm assumed linear rate

A force of 4067-2793 (N) compresses the spring by 310-232 (mm)
1274 / 78 N/mm
16.3 N/mm
uncompressed lenth guessed 480 mm assumed linear rate

That is quite soft by todays standards...are you sure about the data?

I would not take the effort to go for the big diameter springs.
With a common small diameter spings as you have them, you can easily exchange spring rates to make the suspension suit your liking.
I would not consider that "unhistoric"...

Thomas

You're such a helpful guy Thomas!

Not doubting your maths for a moment - it got me thinking - internet and all....

searched on Google with 'spring rate calculator'

http://www.pontiacracing.net/js_coil_spring_rate.htm

I guess there are others, none that I wrote, sadly.

GC

Thomas, and CG

Most helpful data !

Re certainty of the data ; This is the data from 131 Abarth Rally original data book . I guess this pertains to Stradele though.

I have made the following logical extrapolation in my email to the spring manufacturer :( would like to post his link with GC permissieon ?)

I have found the following specs on 131 Abarth Stradale (street version).

FRONT
Fiat (Abarth) part number: 4335641
Height of spring under load of 3156 + / - 127 N (322 + /- 13 kG) = 270 mm
Minimum load to compress it to the height of 194 mm = 4459 N (455kG)


REAR
Fiat (Abarth) part number: 4151719
Height spring under a load of 2793 +/- 127 N (285 +/- 13 kG) = 310 mm
Minimum load for the height of 232 mm = 4067 N (415kG)

Note that the springs internal diameter should be exactly as on the 131 sport (aka :Racing) - (ca. 100 mm)

As you know they made only 400 of these 131 Abarths just to qualify for FIA gr.4, so data is scarce.

I will use the car for vintage competition rallying (on tarmac), while the Stradale was really a civilian street version car they sold to general public .

I know that the competition cars had lost of unregistered modifications done to them, and suspension was probably one of the most often modified elements. They had as many versions as there are surface kinds (tarmac, gravel, mud, snow) and each driver had his own settings/ specs). We however need to work out only one for tarmac and for only one driver ; myself. Also this car will not rally for FIA world championship, but needs to be safe and handle well on hard paved curves.

I believe however that if you can interpret the old fashion data on the Stradale springs , we will be able to figure out pretty close combination.

By experience I know that the ones used for Stradale on the front will be hard enough for the rear (though they will be probably 1,5 coils too high ) (which should translate into 3,5 -4.0 cm suspension height with the car on the wheels).The hardness on the front should be higher by the same ratio as front to rear. For example : if the standard front to rear hardness ration is 1.3 :1.0 , my version of fronts should e 1.3 x the standard fronts . As to the height they should probably be fronts should be of the same length as original fronts. Both front and rear will be adjustable and thus we will be able to fine tune them.

Note that the car will carry no load except for driver, co-driver and petrol !!! It is not used for civilian use - vintage competition only- thought it is road legal.


Does this reasoning make any sense ? It is based on my standard springs experience.

Re: Unhistoric: You are right I do not think the solution based on modern shocks and springs is not unhistoric. It currently looks like at least initially I will keep my "unhistoric" Bilstein on the front and my "unhitoric" Koni on the rear. However since I got my hands on original GR 4, front turrets and inserts and original rear turrets I want to rebuild it based on original parts . It will probably be a trial and error process but in some time we should be able to get this right as well. Any assistance in this process will be greatly appreciated.

NOTE that the front spring diameter of 100 mm is forced by presence of grease nipples on the turrets ( bodies). The cylinders are 500 mm in diameter , with the body it is almost 6omm and the nipples are 12mm , so we need to clear 72 mm . the 100 mm diameter gives us just 14. mm on each side. which I believe is the minimum to clear it some safety margin.
Miro

UPDATE :

The rear springs used so far are original front 131 springs shortened by 1.5 coil.
The shocks I used for rear standard suspension (which worked perfectly) and the springs will be up for sale.

Problem with suspension coil springs resolved!

After brief exchanges with Neil of Coil Spings (1989) Ltd ( http://www.coilsprings.co.uk/) we have translated scarce data into real life specs.

Neil proved to be extremely knowledgeable , helpful.

If anyone needs springs he can do them any size any hardness this is the place to turn to ! .

Miro

PS : final order is like this

FRONT
25.4 N/mm
393 mm

REAR
24.2 N/mm
424 mm
INSIDE DIA. 100 MM.

Engine arrived!

Here are first pictures of this beauty !

Issue of what oil to use for the LSD is resolved : CASTROL SAF-XJ 75W-140

Miro

See this for detailed description of the spring mounting problem :

"Conversion to abarth suspension problem HELP PLEASE !"

viewtopic.php?f=14&t=2176


Miro

In the mean time the diff was positioned
in preparation for building the top diff hanger plates.

See the original plates we will try to replicate :

W have also reinforced the original support for the arms supports and reaction rods :

This is it for the day !

More to come...


Miro

Ok, the diff is hanging

The "hanger is different than original , but :

1. I did not have anything to copy and had to make it from scratch;
2. the builder decided this would be the strongest he can manufacture
3. nobody will look see this part from underneath
4. I did not have any better ideas and it really looks strong.

Miro

PS this will be fully welded on both sides and the fins will e welded together too, so it should be at last as strong as original and not too much heavier.
Minor adjustment required to make sure it does not collide with the diff bolt and nut of the housing ...

Did I give this 'MODEL POST' status yet?

I think not.

'MODEL POST!'

GC

Dear Guy ,

Thank you for this recognition, indeed.

The opportunity to share all this is very much appreciated and I owe this to the GCRE forum.

Miro

I am so glad this is such an exclusive forum with racing gentlemen members ONLY !

Some important progress:

One of my friends from Belgium friends took pictures of the top mounting turret modification. This is the later version , which has been developed for the "new" - spherical bearing based top mounts for the struts.
Previously the original front top mounting was used.
This is essential to understand the options. Currently , the solution will use currently will the "original" - based on the same top mount as used in Mk 1 on the front , which requires no major cutting and welding.

However I have already ordered the spherical top mounts with matching strut tubes (housings).
I have also ordered from a friend from Turkey whole rear towers.
These will be the towers, that we will be modified and replace the ones currently installed once the top mounts are received and he final springs as well as original strut tubes are ready.

Ooff ... it certainly is not and easy and quick task to modify standard 131 rear suspension to Abarth standards.

It seams that 70 % of the problem is lack of information and 70 % lack of parts.

Hopefully we have passes the middle point. thought we have already definitely passed the point of no return...

More to come as we make progress ...

Miro