My last Subaru was a 1998 Liberty RX, 2.5L, cat back exhaust, cold air intake, power chip tuned for 98RON petrol. When i 'compared' it against a friends 01 Impreza RS, my car would leave his for dead, so its fair to say my heavier car had a decent increase in power
That said, it still pulled a 15.72 down the 1/4 mile. Mat has pulled 13.5 in a 1997 wrx with a cat back exhaust down the 1/4. you can make improvments, but you are pretty much wasting your money if you do. save the cash you would waste on a WRX half cut. Have a squiz at
www.japanesewholesale.com.au for rough prices