Hi UnoCento/JW,
As 1986Uno45S said, 'branches' are most likely to be tubular extractors that replace the original cast-iron exhaust manifold. And, I also agree that for a quick 'hit', you can upgrade the air filter box and the exhaust back box to make a better sound (and not much difference to power
)
The design of the original cast-iron exhaust manifold (Americans call this a 'header') - and the rest of the exhaust system - is not something that happens by accident. I think FIAT would have spent quite a lot on designing those parts
I'm of the view that if you upgrade one part of the system, you must upgrade some other part as well to notice any real benefit. And it has to be done by someone who knows what they're doing (or who copies the original system faithfully with only slight changes).
Also I feel that the exhaust is less of a restriction than the intake system - the single-point injection is basically a single-carburettor as far as intake airflow goes. There's room for much improvement.
So - to install 'branches' (extractors), you should also replace the rest of the exhaust with one that has a larger tube diameter (but not too large; say, 1-7/8"), AND you should raise the engine compression, change the camshaft, fit multi-point injection, and re-map the injection and ignition systems.
With changes on that sort of scale, you'll get noticeable increases in power and torque. Again, the changes have to be made by someone who knows what they are doing, ideally with experience of FIAT engines, but at least with experience of similar-sized engines.
With a car like the Uno (one where originality is not much of a concern), it's usually more financially-economic to drop in a different engine (engine swaps have been discussed here many times; do a search for 'engine swap').
Just my thoughts,
-Alex
