Headers are one of the top aftermarket bolt-ons you can put on to your engine to make power. Most cars come with a cast design which is cheap to produce and very durable, however not very good for flow. What a header does is give each exhaust port its own primary tube which will give the exhaust gas a longer distance to travel meeting up with the other exhaust gases which meet up in the collector which allows for a smoother transition of the gases allowing for more exhaust velocity.
There are two typical types of headers. Shorties and long tubes. Their names are exactly what they imply. Shorty headers are short in design with short primary tubes which allow for gains through out the whole RPM range, results will vary depending on how restrictive the stock design is. Shorties are great when space is limited or if you're looking for a direct bolt on unit. If you are looking for maximum flow and gains you'll have to put on a long tubes. This design allows your engine to really breather properly. To make your engine really happy try to find a set of equal length long tube headers. By having each exhaust primary the same lengths all the exhaust pulses will meet in a smoother fashion when they hit the collector. Keep in mind long tubes are an expensive route. The exhaust has to be modified all the way to the catback system usually meaning relocating the catalytic converters.
Headers can come in a variety of coatings, from a light coat of paint to prevent rust while in store to high heat ceramics. Ceramic coatings are the way to go, inspite of their added cost there is a lot of benefit to this treatment. The ceramic coating keeps the heat in the header allowing for cooler under hood temperatures, saving items like the electronics under the hood. The coating is also very durable so your headers will look good for a very long time.
Catback systems offer a lot of "bang for your buck". You get looks, sound and performance. For everyone considering an after market exhaust I recommend purchasing the kit which is designed for your car. Most people that buy cat-backs or full exhaust systems have relatively stock motors. A lot of people believe that having no back pressure is that best thing for the engine in order to make power. This is a misconception because only horsepower is on their mind. Keep in mind that horsepower is a bi-product of torque.
Bigger is not always better! With too big of a pipe diameter your motor will lose a significant amount of bottom end power killing your off the line performance. Exhaust companies such as Magnaflow and Flowmaster pick a pipe diameter relative to the amount of air your engine can flow and increasing air velocity potential. An engine is nothing more than a glorified air pump so having the correct pipe diameter will actually help increase the air velocity of air flowing through your exhaust. The more air you can flow through the motor the more power you can make. A proper exhaust system can actually flow better than just a straight pipe due to better exhaust scavenging (basically means moving all those exhaust gases out of the combustion chamber), resulting in more power. Most V8 kits only go to about 3 inches in diameter because those motors make around 300 HP in most modern applications. If they make more that pipe diameter is still ok. So motors that are 3.8 liters in displacement or 231 cubic inches don't need to be that large. Most exhaust kits are 2.5" or smaller. True a larger diameter might affect the "sound" of your vehicle but I have yet to see a 3inch make more number on the dyno over a 2.5inch system on a stock motor. So if you're a performance enthusiast take all the guess work out of "how big of an exhaust should I go with?" and trust the companies that invest millions into this area and go with what they say.
A proper exhaust system will maintain a consistent diameter all the way through as well. This is accomplished by either mandrel bends or pie cuts which ensures the exhaust gases have a smooth path to take through all the bends.
Proper diameter translates to better efficiency and exhaust scavenging (pulling all the exhaust out of the exhaust chamber allowing for more fresh air to enter) leads to more power and less fuel consumption saving you money.
Good aftermarket exhaust kits will fit in a vehicle with relative ease. Major exhaust companies will prototype their designs, test and then re-test to make sure their design will have proper clearance under a vehicle. A lot of systems now a days come with all the necessary hardware in order to install the catback system in your driveway over the weekend. I would however recommend welding all the joints of the exhaust system to ensure a very solid and leak free installation (weld around the entire pipe, don't just to tac welds!).
Choosing an exhaust system that uses high quality materials will not only make sure your vehicle look good, but will also save you money. Choosing a system that uses high quality stainless steel means it'll be the last exhaust system you'll put on your vehicle, and owning your vehicle for longer will save you thousands of dollars.
HIGH FLOW CATALYTIC CONVERTERS
Catalytic converters are placed a little after your headers or exhaust manifolds. They act like an "after burner" helping eliminate a lot of emissions that your engine produces. Unfortunately they are a source of a lot of restriction. A lot of people cut them off, I however do not believe in doing this. For one in a modern vehicle with O2 sensors if the catalytic converter is removed the readings the O2 sensors pick up will be drastically changed, usually throwing a code and in turn giving poor performance. Another thing is it's illegal in many places to run a vehicle with out the cats and it's just playing not good for the environment.
You can have the best of both worlds with a high flow cat. You can maintain good flow throughout your exhaust system while trying to burn as clean as possible. If you're going to build a vehicle and make power, you might as well be responsible and try to be as environmentally friendly as possible.
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