Alfa Giulietta Sprint

[sladey]

Weirdo!

Great stuff - thanks for sharing

[911hillclimber]

Villiers Services, a great company!
Interesting 3 shoe fronts, good to see another approach on a different car.

[Mike]

Weirdo!

[Lightweight_911]

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So, the other (nearside) front brake swap over was more or less a 'carbon copy' of the first one - the complete 3-shoe brake assembly was replaced by the std 2-shoe set up ... except that when I came to fitting the drum, I noticed it was another 'Destro' (right side) drum as opposed to the correct 'Sinistro' (left side) drum .

The difference between the 2 sides are the angle of the radial 'fins' which are designed to channel air over the drums to assist in cooling them:



It wasn't a big problem since, as mentioned earlier in this thread, I had (& was about to replace) the 'big rear' brake set up on the car & these utilise the same drums that were fitted as std on the front.

However, I still needed a pair of std 'helical-finned' alloy rear drums so started to search for some.

As you can imagine, there aren't many Giuliettas being broken for spares in the UK these days & those drums that I could find for sale in Europe were mainly fronts. I did find a few rear drums in the US but they were typically only available as part of a set of 4 - & shipping was prohibitively expensive ...

Then, out of the blue, a set of F&R drums popped up on ebay in the UK - not only that but they had been further lightened

I don't know if they'll introduce their own problems - excessive dust contaminating the wheels ? - but I managed to bag them for a good price so worth the gamble.





At the moment I've just given them a good clean & will see how they fare - if they don't present any problems I may get them vapour blasted.

So with the front swap completed it was onto the rears ...


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[Lightweight_911]

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Strip down was much the same as for the fronts except that in order to remove the backplates I had to remove the axle shaft.

The sequence speaks for itself - again, note the lovely lightweight cast alloy brake shoes:












Both 'big' & 'std' rear brakes use the same wheel cylinders & adjusters &, even though I had some spare original Girling wheel cylinders which I had already cleaned up ready for new seals, etc, I decided to swap the existing ones over since I'd previously refurbished them last year.

Backplate assembled ready to go back on the car :



- & with the lightened brake drum fitted:




Last job was to clean up/swap over the thin steel 'torque plate' which fits in the centre of the alloy drum to prevent the steel or alloy wheel from 'biting' into the surface of the alloy over time which in extreme situations can lead to loosening of the wheels.

The same process was then carried out on the other side.

This just left adjusting the shoes all round & bleeding the system ...


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[Lightweight_911]

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Out of curiosity I decided to check what the weight saving for my brake swap was & found that I'd saved a total of 10kg by changing from the 3-shoe/'big' rear set-up to the standard braking system.

Add a bit more for my drilled/lightened drums plus probably another kilo for downsizing my tyres from 165 to 155 & I reckon I've saved ~ 12kg of unsprung weight - a useful bonus !

Next I wanted to try a few minor changes to the Weber carb jetting...

The car had been prepared by the previous owner as a competition car (for circuit racing & hill climbs) & the engine had been built to a 'Veloce plus' state of tune - influenced by the specs of the Autodelta 1300 GTA engines in period.

As such, max power was achieved high up in the rev range (7000+ rpm) consequently sacrificing power lower down - the car wasn't by any means 'intractable' but it had a tendency to run rich in traffic & 'bog down' so I wanted to see if I could improve on this without losing too much at the top end.

Obviously this needs ideally to be done in conjunction with a rolling road but that can work out quite expensive so I wanted to try some alternatives with a view to minimising the time I'd eventually need on the rolling road.

First off was the venturi (choke) size - my engine utilised 30mm chokes which had been bored out to 34mm which is quite big for a 1300cc engine (standard Giulietta Sprint Veloces used 28 or 29mm venturi).

Using Jim Kartalamakis' "How to Power Tune Alfa Romeo Twin Cam engines" as one of my references, he suggests the following formula for determining venturi sizes:

Venturi size (mm) = √A x B
. ....... ............... . 50

- where A = capacity of one cylinder (322.5 for a 1290 cc engine) & B = revs for max power

So, for max power at 7000rpm we get: √322.5 x 7000 = 30.05
........................................................50

So that would be my initial venturi size to try - 30mm

[Lightweight_911]

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For main jet sizing in a modified engine Jim K recommends using between 3.8 & 4.2 x the chosen venturi size, so with the 30mm chokes a good starting point for main jets is 120.

The mains in my Webers were 145 so that seems like a logical change to try (std Sprint Veloce mains were 110).

The only other jetting change I wanted to try at this stage was to the idle jets.

According to Jim K, the sizing of these is entirely dependent on the type of cam used & this is where the problem lies - the cams in my engine are somewhat of an unknown, being 'custom-ground' from steel billet to Conrero specs (one of the period Alfa tuners).

However, most of the smaller capacity Alfa twin cam engines use a 50F11 idle jet whereas mine were 50F8's as used in the 1300/1600 GTA's so I opted to try switching to the F11's ...

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[Darren65]

Very interesting Andy, thanks for sharing

[KS]

Interesting – I was given some advice on this matter by Don who used to run the rolling road at Phaegre Engineering, Hartley Wintney (Denis Jenkinson's old garage). And guess what? Exactly the same formulae! I used it on all my VW motors running dual Webers, and recommended it to others, all with great results. It's a great way to find a starting point before hitting the rolling road.