Upper front A arm weight reduction

Just some images of work in progress on a spare set of 308 upper A arms that I have for my group iv project. Although these are not strictly copies of the Michelotto cars, there is still a useful weight reduction to be had.

All that was required was to draw up a template, check the clearances to the edges etc, then make a centre hole template. I then just used standard Bosch bi metal hole saws in 14, 20, 30, 35, 40mm diameters to remove the material in a standard bench drill press.

The plan is then to shotblast, re-paint and use the energy suspension black bushes.
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The upper front A arms on the michelotto cars look as if they were just drilled, the lower fronts and rears had plates welded in to tie in the U section rails top and botoom, as the pressed parts are only connected on one side. The whole point of the exercise is a reduction in unsprung mass. If you some up the total package it amounts to quite a few kg, see below;

Weight saving in A arms
Alloy calipers plus 2 piece discs (alloy bells) I have 355 parts on my car
Alloy dampers (intrax or similar)

All up in the region of 5-6kg per corner for a given wheel and tyre size. I will add it all up once complete, but this was done whilst I had a week back in the UK, plus stripping out some GT4 rear stub axles which do not have the same stress rasiers that the GTB stub axles have. So the work is not yet complete. You can see more details if you look on www.mat.fi at their project 308's.

 

From what I can establish based on old UK FOC articles plus part history the stub shafts have had 3 evolutions as follows;

Early GT4's to chassis number 12006 had rear stub axle part 106128 (this part is used in conjunction with the cast iron rear upright, it looks like an evolution of the Dino rear upright)
GTB's started with rear stub axle part 124964
This has then been replaced by part number 108046

It is also interesting to note that the early GT4's had cast iron rear uprights and that the cost of the part 106128 is £238.50, i.e. considerably cheaper than 108046 which are £707. I do not know the reason for this, but the earlier stub axles seem to have a very generous radius at the 'T' where it joins the wheel hub i.e. is not a stress raiser and should have improved fatigue life. These are the parts that I believe are the most robust, other than inspecting yearly and/or buying the latest parts.

However the problem does seem to only afflict cars that have had hard use e.g. track days, and or have wider wheels, different wheel offsets,or if the car has had previous damage affecting the integrity of the shaft. Attached is pic borrowed from an earlier thread of the rad in question (marked in red), plus part sheet showing earlier and later rear uprights.

With respect to the upper wishbones the top plate only really prevents 'racking' of the wishbone, the main bending loads being taken by the U section rails. I do not anticipate any major issues with life as the car will only be used on the road, and in fairness wishbones can be obtained fairly cheaply and there is a ready supply. I also have the original parts which are not modified if there are any signs of any problems.
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from caluclation based on material thickness, density of steel, and the diameters used for the holes the weight saving should be approx 90g per arm for the uppers. Sorry did not measure these whilst at home, it seemed more important to get the job done than worry about the total weight saving.

 

I have just used the homologation papers, plus the work MAT have done as the basis for a similar copy. I cannot find any reports that the Michelotto cars ever had any suspension releated issues, but take on board that parts may have been replaced frequently. The other worthy point on this is that the front end loading on the michelotto cars was much less due to the fact that these cars weighed in the order of approx 200kg's less than a fibreglass road car.

Guess I could get some FEA done to be sure but at the moment the car is a long way from being finished so there will be time to run through everything. Will also see how Morten gets on with his car.

 

The whole point is this is just a bit of a hobby (the design of these parts have been poven out on the original michelotto cars), the upper A arms are part of a bigger picture to create a group iv rally replica, the weight saving for the entire car from people that have done this before is approx 200kg - close enough to a 20% weight reduction from a standard euro fibreglass car.

If you take the suspension then it all adds up as follows;

Upper A arm 90g (by calculations)
Lower A arm 120g (by calculations)
Swap out front brakes to 355 plus 2 piece discs - 1.4kg - already on car
Swap out Koni's to Intrax or similar - approx 3-4kg - based on weight data from similar cars

The whole reason for doing this is that the group iv cars just look so good!

 

And some further good news today, Kari has sent me the invoice for the group iv body bits, now it is starting to come together, and for me its worth every penny.