Changed the exhaust (catback) to 55mm, also changed the muffler with an inox sport one (free air flow). The car runs better. At low rpm is fine (as it used to be, no decrease) and at high rpm it seems that it is better.

Does anyone know what is the original exhausts pipe diameter? because i think it was 50mm, but i'm not sure.

 

Also removed the resonator from 1.0, but after testing the car several times, it definetely lost power at low rpm. After that another resonator was put and it was fine at low rpm.

 

 

Also does anyone know what kind of catalyst 1.0 has? is it metallic or ceramic? does it provide free flow?

Not sure about the catalytic, but I believe the stock piping is 2".

My next plan is to upgrade the exhaust also. I want a nice throaty sound so I'm thinking of getting a Borla catback from 4wheelonline.

Do you have the 1.0 125 version?

The catalyst has been inspected (with a camera) and it is alright.
The exhaust has been changed. Pipe diameter 21,6 inches. Free flow inox resonator, free flow inox muffler.
Performance seems increased and throttle response more stable and better.
Sound is more racing, but not annoying, not too loud.

Should the downpipe be larger than the (other) exhaust pipe?

What if they are same size?

The catalyst was changed one year ago.

The new one is euro 6 metallic 200 cpsi (sport) catalyst.

So far nor cel, no error/fault codes.

Performance increased just a bit but the car is performing overall better especially during summer's very hot weather. Fans aren't activate so often as before.

The sound is nice. A bit more sport than before.

 

 

I would never recommend that kind of exhaust's resonator (box).

That with that curved shape inside. This shape is supposed to reduce the noise and keep back pressure a bit (so not loose torque).

It was tested on the first aftermarket exhaust the car had.

It produces a very disturbing noice.

 

 Exhaust with stock catalyst - before sport catalyst and exhaust after sport catalyst's installation.

Downpipe is stock.