I am looking at replacing the back box on my 170, any recomendation on a box that is good value for money (even one that would improve performance if possible)
I was hoping to buy a CAT back system but can't afford to at the mo and just want my ST to sound sweet without spending a bomb at the minute

 

Replacing the back box will not give any performance gains as the standard system is very efficient. Even with a cat back you may only gain 1-2bhp.
Cat back systems usually remove the rear box completely leaving you with only 2 siilencers in the system which gives a nice increase in sound but its not in your face. I have a mogoose cat back system and its no louder than the standard exhaust when plodding around infact its quite understated at full chat too.
I would save up and get a blue flame exhaust as they have a good rep and are under £300

 

The standard system is as good as any mate and was designed to get the best from the engine, what you pay for an aftermarket system and what you gain in BHP is not worth it.

 

Ok cheers for info.
What is a decent back box then that won't affect things too much?
Just want a nice sound

Just seen this on ebay http://cgi.ebay.co.uk/FORD-FOCUS-1-8...item1e597002eb
Is this a blue flame cat back, as have been on their website and looks the same.
If not is it any good?

 

Yes that looks the same as a blue flame and its the same as my mongoose too. Rumor has it that blue flame and mongoose cat backs are identical as in made in the same factory. A decent back box will cost you near on £160 so i would pay the extra for a full sytem. When i fitted mine it definately breathed better, i could feel a noticable increase in the pick up when you put your foot down.