A big improvement will be noticed with a modified exhaust. Allowing a easier path for exhaust gases to flow makes it easier for your engine to breathe. A cat-back exhaust will unleash some good power in your machine. This is basically a larger pipe with less restrictive bends allowing easier passage of those ugly HOT gases. The stock system in your Jeep is made for the Sunday driver going to church. If you are even somewhat of a driving enthusist you will never gain serious power without some kind of exhaust modification. A larger pipe (2&1/2") with a free flow muffler will put a smile on your face right away.A nice exhaust tone will appear as well when you put your foot in it. If your local laws permit (which they never do) you can bypass your catalytic converter and pull another dose of power out of it. All i did is have a bolt in catalytic whenever i needed to get it air friendly for the government boys. This entire system is amplified with an exhaust header. Prices can again widely vary from $200.00-$750.00 Canadain depending on what you want. This would consist of Stainless Steel(the best) down to a backyard Midas job at your local shop. Be aware again and find out before hand that some shops will not remove your Catalytic unless they replace it with another. It should only take a few calls to find a place that will.