'73 Fiat Abarth 124 Rally - project

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miro-1980
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Re: '73 Fiat Abarth 124 Rally - project

Post by miro-1980 »

Thanks Erik,

We have been invited a traditional "end of a season rally" ( Bison Rally organized for 48th time by our WRC champion Sobieslaw Zasada for elite of rally drivers and guests).

We will go with our replica 124 Abarth "as is" - without any further modifications.

There is no time now , but when we return I will certainly ask you for some pictures and measurements.

Thanks

Miro

PS: this is may be good time to present our new team addition...
MANIEK NEW .jpg
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miro-1980
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Re: '73 Fiat Abarth 124 Rally - project

Post by miro-1980 »

Short update on car's performance during 48th Bison Rally/

It is really incredible how the var handles!

Absolutely predictable and even when the rear starts to move sideways , all it takes is a small correction on the steering wheel without taking the foot off of fully depressed gas pedal! This is really a great feeling to drive it on a rally.

The car's standard suspension actually worked very well, Th sports (yellow) adjustable Bilstein shocks on front and rear with standard springs did the trick , though the car was a bit "swingy" on curves .

I can see why so many top drivers of the day really loved it.

When we get a new engine gaining some 80 bhp and full Abarth suspension this will really be fun to drive . cannot wait to get it all done.

In the meantime few pictures from the rally...
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Building a rally car is fun but real fun is driving it ...



Miro
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miro-1980
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Re: '73 Fiat Abarth 124 Rally - project

Post by miro-1980 »

Mick,

When you come back from the trip , please let me know and let's
pick up when we left off re: parts.

Miro
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miro-1980
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Re: '73 Fiat Abarth 124 Rally - project

Post by miro-1980 »

Need help on 124 abarth gear box.

I tried to source one with homologated gear ratios and ..

The only one I have found was from Bacci, but at prohibitive cost of ca. 6500 Euro.

I know the Bacci boxes are very good , but ... need to find a less expensive alternative.

I have seen Hungarian 6 gear dog boxes but the ratios are all wrong.

Does anyone know if Quaife makes the homlogated ratios?

Miro
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TomLouwrier
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Re: '73 Fiat Abarth 124 Rally - project

Post by TomLouwrier »

hi Miro,

How good is your Spanish?
There's a quite active rally scene in Spain around the Seat 124, which means suppliers of parts and equipment. Try searching for "caja de cambios crabot seat 124 5 velocidades" either text of pictures.

Alternatively, I remember Guy working on a Spanish 16v conversion where the late FWD reversed flow head was reversed, creating a 16v 124 with the ports on the historically correct sides of the car. That is a very well engineered project and the owner should be able to help you out regarding possible sources over in Spain. Guy?

regards
Tom
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miro-1980
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Re: '73 Fiat Abarth 124 Rally - project

Post by miro-1980 »

Hi Tom,

Unfortunately my Spanish is non existent.

Will try searching but I may turn more questions than answers ..

Miro
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miro-1980
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Re: '73 Fiat Abarth 124 Rally - project

Post by miro-1980 »

Looking at several options ...
Last edited by miro-1980 on November 13th, 2014, 9:53 pm, edited 2 times in total.
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miro-1980
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Re: '73 Fiat Abarth 124 Rally - project

Post by miro-1980 »

Well ,

The shifting pattern on the Spanish 5 gear dog box seems to quite awkward:
shifting patern on Spanish 5 and 6  gear dog box.jpg
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The Colotti shifting pattern is this
colotti shifting .jpg
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:

Is Bacci the same ?

The 6 gear Hungarian box is relatively inexpensive ( 2 K euro) and has a standard shifting "H" pattern
Screen Capture #438.jpg
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I am afraid that anything else than a standard H would take me 5 seconds to kill the box permanently on the first try to shift.

As far as the gear ratios are concerned : the originally homologated were :
124 abarth.jpg
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The Clotti did not give me details but indicated that the 1:1 straight ratio is in 5th gear - not the 4th, which means the gear rations are different than homologated. The cost 7500 Euro for the kit

Bacci gear ratios also do not match the homologated ones :
Bacci 124  ratios.jpg
Bacci 124 ratios.jpg (29.2 KiB) Viewed 21449 times
The cost is 6500 Euro

Conclusion: the 124 abarth dog gear is a costly item , and it is not available in originally homologated gear ratios.

Getting something reasonable will not be easy and will require compromises, unless onethinks about an original ... But an original dog box will be beat up and require parts ( which are apparently not to be bought .

So we are beck to square one ...

Miro
Last edited by miro-1980 on November 13th, 2014, 11:19 pm, edited 1 time in total.
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miro-1980
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Re: '73 Fiat Abarth 124 Rally - project

Post by miro-1980 »

Looked at some details of the Hungarian box and it actually looks pretty good ...
variant 2 graph a .jpg
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variant 2 data.jpg
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I have selected final diff ratio at 10/45 to make it mildly short .

Also the gear ration selected (so called variant 2) was selected to be short but well spread over the RPM range giving each gear a reasonable operating RPM range.

The gear ration are significantly different then Corsa , but given this is a 6 gear box i believe this is reasonably "close" to the Corsa.

124 Abarth Corsa ratios were as follows:
original.jpg
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All this for just less than 26% of Colotti and 28% of Bacci. The Hungarian hard steel 6 gear dog box for 124 1800 is just above 2 K Euro.

(I'd' rather add the difference to my engine budget.)


Guess that the choice is clear.

Miro

PS: I called some friends who use the Hungarian box for their historic rally cars and I heard : " rallied this box hard for 3 year and - no problems".
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miro-1980
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Re: '73 Fiat Abarth 124 Rally - project

Post by miro-1980 »

Brake progress:

I was able to find a nice original set Abarth brakes :
set of 124  gr 4 brakes  .jpg
set of 124 gr 4 brakes .jpg (81.91 KiB) Viewed 21363 times
front : 256 unventilated disks (12.4 thick )
2 x 48 ATE calipers
matching front mounting brackets
rear: 256 discs (9.6 thick)
2 x 34 ATE rear calipers.
we will manufacture the brackets locally

As the rear calipers are without handbrake I will have to use a separate handbrake caliper.

Luckily , we have a spare matching ATE caliper for the hand brake on the shelf

hand brake caliper .jpg
hand brake caliper .jpg (55.9 KiB) Viewed 21363 times
and the Abarth hubs can accept two separate calipers.

We should be pretty much done with brake parts.

Miro
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TomLouwrier
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Re: '73 Fiat Abarth 124 Rally - project

Post by TomLouwrier »

hi Miro,

Original parts, good for you mate!
Same pistons, not ventilated, discs 13% larger diameter. On paper not much of a shocking upgrade, but the double piston (fixed) calipers should give better response and a bit more efficiency. Nice to see they kept strictly to the original static balance F/R. You could conclude that the street version was in fact quite well designed in the first place.

regards
Tom
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miro-1980
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Re: '73 Fiat Abarth 124 Rally - project

Post by miro-1980 »

Thanks tom,

The original design was in fact quite good.

In judging the advancement of r gr. 4 over a street version one has to remember the historical context. The need to regulate the allowed modifications arose already in the 50's. The first appendix J was issued in 1961. The "arms race" continued and the J appendices become more and more specific and increasingly restrictive. The arms race came to its peak in 70's and early 80's culminating in the short lived group B , which was designed to liberalize restrictive regulations of J appendix for other groups. Allowing the group B monsters to rally proved to be a grave mistake.

Originally the rally cars were really quite close to mass production street version. They were obviously becoming increasingly dissimilar to the street cars only. The first ones were in fact street cars. At the end of 196o' and beginning of 1970's the differences between a street and a rally car were already quite significant though not even close to where we are now , when a rally car just looks similar to a production car and inside it is a completely different vehicle.

At the time of g1-2-3-4 FIA required a minimum of 400 to 1000 production of a homologated model. Thus all rally cars were uprated street cars.

The '73 124 Abarth is a good example. The engine was only moderately tuned up. The main changes were in suspension and differential. In fact the 3 times WRC champion 131 Abarth used exactly the same diff and 124 Abarth suspension just adapted to the 131 body. The brakes were uprated from 227 to 256 ( by 13 %) and the calipers from 1 x 48 to 2 x48 (which is double) and the friction area from 62 sq cm to 80.65 sq cm which is 30%. This in total is not an small increase of braking power at all !

But the success of 124 (which was not crowned by a WRC constructors title) lead directly to Lancia Stratos (3 such titles) and Fiat 131 Abarth also 3 titles followed bu Lancia 037 (one title) and Lancia Delta/ six WRC titles.

Fiat 124 Abarth was just the first stage of this long and successful journey of 13 WRC titles for Fiat. of which all but 3 were win on the Aurelio Lampredi designed DOHC engines.

So the 124 Abarth of 1973 has to be seen as a precursor of the Fiat rally success from mid to 70's until 1992 when Fiat pulled out of WRC.

This is exactly why this very model (1973) launched at the start of WRC is so appealing to me. It is a grand daddy of all the Fiat (Lancia) WRC winners , of special importance in the history of WRC rallying .

Miro

PS: Exactly as you say: "You could conclude that the street version was in fact quite well designed in the first place". This is the essence . At that time WRC was a test of how well designed were the street cars and now WRC is the test of how well you can design a rally car. This is exactly why watching historic rally cars in action is exciting and watching current WRC is so boring . If you buy a VW Polo or Hyunday i-20, Citoroen DS3 , Ford Fiesta I do not get even a small of its rally version. Not o to mention that there are only 4 makes in WRC today, while there used to be several dozens.
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Re: '73 Fiat Abarth 124 Rally - project

Post by TomLouwrier »

hi Miro,

As usual we seem to agree on almost everything here. But...

You can only count the piston area on 1 side of the disc when comparing them! The original 124 items are sliding calipers with one 48mm piston providing all the force @ twice the travel. The caliper moves the other way, pulling the second pad against the disc. Clamping force is line pressure x piston area.
The uprated ones you now have are fixed type with a single 48mm piston on both sides, each providing the same force at half the travel.
Effectively these calipers yield the same clamping force @ same line pressure! We've been here before, remember? viewtopic.php?f=14&t=1901&start=90

Extra brake pad surface will help with heat dissipation and wear, but will not increase braking force as such. It's clamping force x friction coefficient, full stop. So plus 13% is all you'll get, maybe a bit more due to the fixed calipers being more efficient (no stick slip in the lock wedges). But not double or even over that. Sorry.

regards
Tom
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miro-1980
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Re: '73 Fiat Abarth 124 Rally - project

Post by miro-1980 »

Ho, ho...

2 x 48 is double 1 x 48 ( but only on paper !)

I am very well aware of the fact that it WILL not double the braking power.
I was just talking the "pure numbers" not dynamic results.

Incidentally , the brake efficiency issue is far more complex than most imagine. You have demonstrated this many times.

For the benefit of less experienced readers let me just stress that braking consists of three key elements: size, pressure and friction. But as a dynamic process the ability to slow down /or stop varies depending varies with other factors as temperature. It also involves the same 4 key elements of the tires as well as such factors car weight, disc material, pads material, road surface, to name just a few .

When comparing braking effectiveness of different discs and calipers combination we assume all other elements being constant, which they never are. While this is fine as regards all except temperature, this has to be given special consideration.

In sports brakes are not working under average conditions but mostly under extreme conditions.

Thus heat dispersion is far more important than in civilian brakes.

Following homologated upgrades in brakes for 124 Abarth and later for 131 Abarth an interesting lesson can be drawn:

The basic gr 4 131 abarth front brake homologation was 2x48 caliper ( exactly as in gr 124 ) but on a 300 mm ventiltated disc. During the running time they tried 4x38 Lockheed and Girling setup but gave it up. The basic front set up held until the end of rallying of this model, with the only variation of a smaller disc of 275.

The rear was 2x38 on a 252 ventilated disc (larger cylinder diameter but smaller disc then 124 ( 2 x 34 on 256 unvented disc).

My observations are as follows:

Given space under 13 inch wheel 256 is probably the largest disc to fit onto a 124. So the 2x 48 caliper must be working well. Importance of vented vs unvented is signified by homologation at a very late stage vented 256 discs for the front.

With more space under a 15 inch wheel in 131 the Abarth engineers went for a smaller rear disc but instead of 2x 34 - for 2x 38.

Abarth designers after a lot of trial and error decided that two elements really count: vented discs and larger discs. But they also seemed to prefer half the number (but slightly larger) pistons than the other way around.

Larger ventilated disks being better than smaller unventilated ones does not surprise anyone. We all intuitively would have the same guess. However, preference of 2 pistons with larger diameter over 4 pistons of smaller diameter is not intuitive at all.

By the way : this is exactly what you have been saying all along including your post just above.

C-h-e-e-r-s

Miro
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miro-1980
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Re: '73 Fiat Abarth 124 Rally - project

Post by miro-1980 »

GREAT RALLY SEASON IN THE NEW YEAR TO EVERYONE ON GCRE FORUM !

Miro

PS: the work is progressing slowly as we are still collecting all the required parts. But things are looking good.

Hopefully , the car will be ready by early July.

By ready I mean the Abarth suspension and brake system in place. Looks : the rear lights , side markers and door handles as in a genuine piece. Interior stripped : carpeting removed, inner side door panels replaced with simple flat light material, big handles replaced by small ones. Dash - like in a gr 4 car with a Heuer stop clock and a Twinmaster Halda. Vintage map light. Roll cage will be in place. The car will be equipped with a n OMP extinguisher system plus a 2.4 Zero 2000 hand held extinguisher

The seats and safety belts are already FIA homologated.

Engine and ancillaries : new engine 160-180 bhp in place, remote oil filter, oil cooler, in-head thermostat, reduction gear starter, 90 AMP generator, 4-2-1 exhaust header, 2x 44 IDF Weber carburetors, mash filters with no air box, Two Red Top fuel pumps will feed fuel. The tank will be filled with anti explosion filler.

Gearbox: standard 5 gear with steel Porsche type synchro wheels. Hellix metallic clutch.

Brakes : 265 unvented discs front and rear , 2x 48 front and 2x 34 rear calipers, 2x 38 handbrake caliper ( if we can fit it onto a 13 inch wheels with a separate handbrake BMC. ( we will make it in-line if the 2x 38 caliper cannot be fit in the 13" wheels) . The servo will be removed. The single BMC will be ereplaced by a bias adjusted twin Girling BMC's.

This will be enough to rally in 2015 but will not be a finished project.

Remaining elements will have to wait for the new 2016 season.

Updates with pictures as we go along.

Wish me luck

Miro
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