Power loss from exhaust mods?

I have a 2.75 inch exhaust system all the way from turbo to tip. It consists of center box and back box but no cat. The pipe is continuous from downpipe through the center box, over the wheels to just before the start of the back box where there is a flange join. The car has been tested to 315bhp, but that was a while ago and before my ownership.


I'd like to get legal and would like to add a sports cat without loosing power. Since 2.75 inch parts are hard to find on ebay/Web I'm considering the following :

Cut out center box, replace with 2.75"/3" expander connected to a 3", 200 cell sports cat connected to a small center box with 3" pipe fittings connected to 3"/2.75" reducer back into main pipe.

Can anyone give me a guess as to how much power this might cost?

Is there better way to add a cat?

Should I just get a complete spare system for mot time?

Just trying some forward planning for once!

Top gear in st.albans fitted a 100 cell race cat on my powerflow system witch I think was 2.75, may be worth finding your local powerflow dealer.

Probably no power loss.

Jst do what most of us do and keep a cat for mot time, only takes couple min to swap over!

No power loss frm putting cat back on??
Sure as hell does!! Without cat my wheels spin at full chat yet doesnt when cats on!! Not very.sicentific like but does show how much power you loose without that freeflowing air!

Is that a 3" Hi flow cat or the std one?

i never lost any power with a sports cat on well nothing noticeable anyway.

I doubt you will lose any power. Also being a fiat owner we go to mechanics so many time we get to know the guys there n they pass your car anyway.

Well they do mine anyway never once even had a car on my car apart from its birth.

Not sure if its high flow but yea its 3inc cat, got full 3inc exhaust system
you see.. but even though its 3inc cat it definitely drops performance when put bk on for mot..
As i said befor without cat i floor the loud peddle and my wheels spin but soon as cats on for mot she wont spin at full chat!! Make your own minds up! Lol