Can anyone recommend an awesome performance muffler or exhaust system for my 2009 S40 2.4i non turbo ?

 

EST has a good sounding exhaust for the 2.4i's.
Eurosport Tuning: EuroSport Dual Sport Stainless Steel Cat Back Exhaust Kit - S40/V50 2.4i FWD
Or you could go custom and save a few dollars.

 

Do you know of any performance chip to improve horsepower and gas mileage ?

 

Go custom and save a lot of money, and for chipping, make sure your chip is last mod. and i would go with custom tune over chipping, so if you ever add anything you can just go back and get it re-tuned. Also please use the search bar before posting a thread, most likely there is one about it already.