One of the first things most riders do when they first purchase a bike is change out the stock exhaust system with an aftermarket motorcycle exhaust. If you have a sport bike you may just opt for some slip-ons. A cruiser will usually require a full exhaust system. The benefits of aftermarket systems is an increase in power as well as that it will improve the sound of the bike. When you get your bike from the factory the baffles usually restrict the sound of your bike so much that it can be barely herd as well as restrictions in exhaust flow are in place which restrict the horse power. The other most significant factor especially on sport bikes is the weight reduction a full race exhaust system can offer.
If you are the proud owner of a Cruiser you are most likely to replace the stock exhaust system with an aftermarket system. Their are many manufacturers available for cruisers. Cobra, Vance and Hines and Samson are just a few. Most of these will reduce the weight of the stock exhaust system by about 15 pounds, increase the performance of the bike and will make it louder. A new system will run somewhere between 300 to over 1000 dollars depending on the system you choose. Cobra makes some nice exhaust systems at a very affordable price. If you have a V-Twin whether its a American or metric bike a new motorcycle exhaust will make the bike sounds ten times better then any stock exhaust. If you do decide to drop the OEM pipes and go with an aftermarket system you will need to adjust your carburetor or have someone remap your fuel injection system in order to accommodate the new pipes. If you do not you will find that the bike will not perform properly or it may even cause engine damage. If you have a fuel injected bike you will likely need to buy a power commander to make the adjustments needed to accommodate the new exhaust. When figuring out the cost of getting a system make sure you figure this in to the equation. I recommend that you have the system installed and the bike tuned by a reputable motorcycle shop.
OEM Exhaust Systems on Sport Bikes have become fairly decent, however many restrictions are still put in to the OEM systems due to laws that have been passed. For a sport bike you will tend to have a choice of just replacing the Cans or replacing the whole exhaust system. This is really a matter of how deep you want to get in to it. Re tuning is going to be needed either way, the only real question is if you want to spend a few hundred bucks or a thousand or so. Usually their is significant weight reduction by going with a full system replacement versus just the slip-ons. The Slip-ons are the cheaper way to go and still get the most bang for your buck. You will definitely need to get a power commander to remap the fuel injection. A lot of the newer liter bikes that are coming out already have a full titanium exhaust system on them so all you need is to replace the cans to take out the restrictions. For those that want to really skimp, especially on the newer bikes with the lower side mount exhaust you can get away with removing the exaust can and placing a beveled open slip on over the end of the pipe, and with the proper dyno and mapping can gain 2 to 8 hp. The draw back is that it will be extremly loud and will not pass emissions and will be subject to ticketing. Their are lots of manufacturers to choose from when picking a aftermarket exhaust for a sport bike. Here are a few: Cobra, Vance and Hines, Two Brothers, Yoshimura, Jardine to name a few. Choosing one is just a matter of taste.
Remember not matter what system you decide to go with it is important that you get the bike tuned to it to get the best performance form your bike. It is recommended that you have the exhaust system installed and the bike tuned by a reputable shop