Aftermarket exhaust parts
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Aftermarket exhaust parts are intended to replace the factory fitted exhaust components in order to gain a performance increase. Some aftermarket parts are designed to improve the look and sound of the car, rather than its performance. In general, the goal of aftermarket exhaust systems is to increase the engine power by reducing the back pressure of the factory exhaust system. Frequently a side effect of a free-flowing exhaust system is the increased engine sound, which is desirable to some people. Aftermarket exhaust parts can also be a styling upgrade by change the visible parts of the exhaust like the exhaust tips.
It should be noted that the intent of any aftermarket component is not necessarily to modify the appearance, sound, or performance of the vehicle in question. While that is almost always the goal if the aftermarket component is replacing a fully working or perfectly good component, it is frequently the case that when the stock or factory component has worn out that an aftermarket component is either more widely available (or less expensive) than a factory or OEM replacement.
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[edit] Common aftermarket exhaust parts
[edit] Headers
Switching from an exhaust manifold to exhaust headers (also known as extractors in Australia) will decrease the amount of back pressure and in turn increase the high-end power of the engine. This is done by using an individual pipe for each exhaust port that has smoother bends, decreasing airflow resistance. The pipes then merge together at a collector and then flow into a larger pipe (down pipe), just before the catalytic converter. In equal length, headers as each exhaust valve in the head of the engine is opened and exhaust gas is forced out it passes down one of the header pipes, and through to the down pipe where the exhaust gas velocity causes a slight vacuum in another header pipe. This has an effect of sucking exhaust gas from the cylinder next releasing exhaust which is beneficial for performance. Exhaust headers can be of tuned length to perform best at specific RPM ranges. Stock exhaust manifolds are usually made of cast iron, and can be restrictive. Headers may or may not increase the dB level of the exhaust, depending on the original exhaust manifold it replaces and the engine. Headers can be ceramic coated to reduce the heat radiated in the engine compartment, and to increase the temperature of the pipes which increases the velocity of the exhaust gases.
Terminology:
- 4-2-1 Headers where 4 pipes merge into 2 which merge into 1
- 4-1 Headers where 4 pipes merge directly into 1
- Shorty Headers where each exhaust pipe travels the shortest distance from the exhaust port to the collector cup
- Equal Length Headers where each exhaust pipe is the same length from the exhaust port to the collector cup
[edit] Catalytic converters
Catalytic converters are necessary to reduce emissions but create back pressure due to the exhaust gases being forced through a catalyst, and therefore decrease high end engine power. Many modern catalytic converters only produce 1-3 psi of back pressure. Hi-flow catalytic converters can replace the standard units in order to provide lower backpressure. Installing aftermarket catalytic converters is restricted by law in some countries.[1]
[edit] Mid-pipe
The section of tubing between the catalytic converter(s) and the rear muffler on cars that have two parallel exhaust pipes. Performance mid-pipes often have a perpendicular connecting pipe or the pipes temporarily merge. This is to equalize the pressure in both exhaust pipe and keep the engine back-pressure as low as possible since back-pressure is detrimental to high end power.
- H-Style Pipe where there is a perpendicular connecting pipe, resembling the letter H
- X-Style Pipe or X-Pipe where the exhaust pipes temporarily merge, resembling the letter X
[edit] Glasspacks
Glasspacks (commonly called cannons) employ two tubes, an inner perforated one, and an outer solid one. Between these tubes, there is sound insulation. These mufflers decrease back pressure and don't decrease the decibel level much. Glasspacks can be used to give the engine a deeper "throaty" sound.
[edit] Silencers
Silencers are a series of concentric pipes around the exhaust pipe. These concentric pipes allow sound to travel into them and cause the sound waves to bounce off the closed, flat, ends of the pipe. This reverses the direction of the sound waves making them collide with oncoming sound waves and cancel each other out. This design is usually very free-flowing but does not offer as much sound reduction as muffler.
[edit] Resonators
Resonators, also known as Helmholtz resonators are sections of exhaust pipe that expand to a larger diameter and allow the sound waves to reflect off the walls and cancel out. Resonators are mostly used to reduce raspiness and popping. Resonators are similar to an Expansion chamber, only for 4 stroke engines. They do not produce much back pressure.
Many North-American cars (and possibly cars in other parts of the world) made since the early to mid 1990's can have up to 3 distinct (but similar looking) exhaust components downstream from the catalytic convertor(s). Each of these components may be called resonators or mufflers. Usually only the last component is the actual muffler, and the other components are the resonators.
[edit] Stock mufflers
Stock mufflers typically bounce sound waves off of the back, front, and sides to cancel out sound. They also increase back pressure, but are very effective at reducing the sound levels.
[edit] Exhaust piping
The piping that connects all of the individual components of the exhaust system is called the exhaust pipe. Contrary to popular belief, the largest diameter exhaust pipe is not always better. If the pipe gets too large, the exhaust gases will cool down, and become more dense and therefore require more force to propel them out of the pipe, which consumes horsepower. And the risk of running a pipe that is too large will decrease a car's ground clearance leading to the exhaust being damaged when the car moves over an uneven surface. Sometimes very loud.
[edit] Construction
While it was common for the stock or factory automotive exhaust system to be made from ordinary (and sometimes "aluminized") steel, some manufactures (such as Chrysler) have been using stainless steel for the entire exhaust system (pipes, mufflers, resonators) since the mid to late 1990's. The use of stainless steel has made it possible for the exhaust system to last for practically the entire life of an automobile. This is a considerable improvement given that in some locations (such as the North-American rust-belt) it was quite common for ordinary steel exhaust components to fail after 3 years of service.
[edit] Performance
Free-flowing exhaust systems may maximize peak horsepower; this is typically accomplished by making the path as straight as possible, using a consistent diameter throughout the system and eliminating obstacles such as catalytic converters and pre-catalytic converters or by replacing the muffler with a less restrictive (and usually louder) one. In a normally-aspirated engine, this often results in a loss of back pressure which may negatively affect low-end torque. (Forced induction engines are not as susceptible to this side effect). Furthermore, eliminating catalytic converters and other emissions control hardware will often render the vehicle illegal for street use in many jurisdictions.
[edit] Advantages
- An increase in peak engine power.
- Mileage can be increased.
- Engine sound is more noticeable.
- Factory or OEM replacement part is not available (or is more expensive)
- Aftermarket part is available in stainless steel (but OEM part is not)
[edit] Disadvantages
- Most modifications increase the noise level and can interfere with vehicle noise level laws.
- Some aftermarket systems can decrease car ground clearance and can be easily damaged.
- Modifications of the exhaust system can interfere with pollution laws in some countries.
- Loss of torque at low engine speeds on stock engines which are not re-tuned for the flow capability of the new exhaust system.
[edit] Aftermarket manufacturers
There are several companies that offer ready-made exhaust kits for certain cars. Some also offer custom fabrication and universal fit applications. Some better known companies include QuickSilver, Borla, Flowmaster, Magnaflow, Edelbrock, and AEM. Other manufacturers (or brands) are Milltek, Rogue Engineering, Walker and AP Exhaust.
