First off, most stock exhausts are made of steel so they can stay cool under high temperatures which allows the car’s engine to run properly. Aftermarket performance exhaust systems are usually made from lighter materials such as aluminium or titanium, which means they will heat up much quicker and transfer more power to the engine – but only if you let them cool down properly. 
Improper installation of an aftermarket performance exhaust can result in damaging your car’s engine by allowing it to overheat or even melt down completely due to the excess heat from the exhaust system.
Next, you need to consider the type of car that you have and what kind of aftermarket exhaust system will work best for it. Different vehicles require different types of exhaust systems, so be sure to choose one that fits your needs. If you have a sports car, you may want to look into an aftermarket performance exhaust system with a muffler that reduces back pressure while still allowing extra airflow for added horsepower. 
If you have a truck or SUV, you might want to consider getting an exhaust system with a resonator which will reduce the sound level of your engine and give it more power without losing any HP.