Below we have listed many common terms used to talk about Exhaust Systems and the related Exhaust components. These are generic definitions and may or may not apply to your vehicle. You can view our entire Exhaust Section Here.
Manifold or header
In most production engines, the manifold is an assembly designed to collect the exhaust gas from two or more cylinders into one pipe. Manifolds are often made of cast iron in stock production cars, and may have material-saving design features such as to use the least metal, to occupy the least space necessary, or have the lowest production cost. These design restrictions often result in a design that is cost effective but that does not do the most efficient job of venting the gases from the engine. Inefficiencies generally occur due to the nature of the combustion engine and its cylinders. Since cylinders fire at different times, exhaust leaves them at different times, and pressure waves from gas emerging from one cylinder might not be completely vacated through the exhaust system when another comes. This creates a back pressure and restriction in the engine's exhaust system that can restrict the engine's true performance possibilities.
A header (sometimes called extractor in Australia) another name for a manifold,is specifically a manifold designed for performance. During design, engineers create a manifold without regard to weight or cost but instead for optimal flow of the exhaust gases. This design results in a header that is more efficient at scavenging the exhaust from the cylinders. Headers are generally circular steel tubing with bends and folds calculated to make the paths from each cylinder's exhaust port to the common outlet all equal length, and joined at narrow angles to encourage pressure waves to flow through the outlet, and not back towards other cylinders. In a set of tuned headers the pipe lengths are carefully calculated to enhance exhaust flow in a particular engine revolutions per minute range.
Headers are generally made by aftermarket automotive companies, but sometimes can be bought from the high-performance parts department at car dealerships. Generally, most car performance enthusiasts buy aftermarket headers made by companies solely focused on producing reliable, cost-effective well-designed headers specifically for their car. Headers can also be custom designed by a custom shop. Due to the advanced materials that some aftermarket headers are made of, this can be expensive. Luckily, an exhaust system can be custom built for any car, and generally is not specific to the car's motor or design except for needing to properly connect solidly to the engine. This is usually accomplished by correct sizing in the design stage, and selecting a proper gasket type and size for the engine.
Header-back (or header back) is to the part of the exhaust system from the outlet of the header to the final vent to open air — everything from the header back. Header-back systems are generally produced as aftermarket performance systems for cars without turbochargers.
Turbo-back (or turbo back) is to the part of the exhaust system from the outlet of a turbocharger to the final vent to open air. Turbo-back systems are generally produced as aftermarket performance systems for cars with turbochargers. Some turbo-back (and header-back) systems replace stock catalytic converters with others having less flow restriction.
With or without catalytic converter
Some systems (including in former time all systems) (sometimes nowadays called catless or no kitty) eliminate the catalytic converter, which may or may not be legal depending on place and whether the car will be driven on public roads.
Cat-back (also cat back and catback) refers to the portion of the exhaust system from the outlet of the catalytic converter to the final vent to open air. This generally includes the pipe from the converter to the muffler, the muffler, and the final length of pipe to open air.
Cat-back exhaust systems are a very popular aftermarket performance enhancement. They generally use larger diameter pipe than the stock system. Good systems will have mandrel-bent turns that allow the exhaust gas to exit with as little back pressure as possible. The mufflers included in these kits are often glasspacks, again to reduce back pressure. If the system is engineered more for show than functionality, it may be tuned to enhance the lower sounds that are lacking from high-RPM low-displacement engines.
Tailpipe and tip
Dual exhaust pipes attached to a car's mufflerWith trucks, sometimes the silencer is crossways under the front of the cab and its tailpipe blows sideways to the offside (right in UK, left in USA looking from the back of the car). The side of a passenger car on which the exhaust exits beneath the rear bumper usually indicates the market for which the vehicle was designed, i.e. Japanese (and some older British) vehicles have exhausts on the right so they are furthest from the curb in countries which drive on the left, while European vehicles have exhausts on the left. The petrol filler flap is normally on the opposite side to the exhaust tailpipe for reasons of packaging (keeping the filler pipe away from the hot exhaust) but also to position it closest to the curb. Of course, many vehicles have tailpipes on both sides, especially those with vee-type engines.
The end of the final length of exhaust pipe where it vents to open air, generally the only visible part, often ends with just a straight or angled cut, but may include a fancy tip. The tip is usually chromed, and is often of larger pipe than the rest of the exhaust system. This produces a final reduction in pressure, as well as prevents rusting of the tips, and can be used to enhance the appearance of the car. These are the least expensive parts of the system.
When a bus, truck or tractor or excavator has a vertical exhaust pipe (called stacks or pipes behind the cab), sometimes the end is curved, or has a hinged cover flap which the gas flow blows out of the way, to try to avoid foreign objects (including droppings from a bird perching on the exhaust pipe when the vehicle is not being used) getting inside the exhaust pipe.
In some trucks, when the silencer is front-to-back under the chassis, the end of the tailpipe turns 90° and blows downwards. That avoids anyone working by the truck when stationary from getting a directed blast of the exhaust gas, but often raises dust when the truck is driving on a dry dusty unmade surface such as on a building site.
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.
-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
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.
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
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.
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.
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.
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.
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.
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.
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.
-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)
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.
You can view our entire Exhaust Section Here. Also check out some of our sound and video clips of different Exhaust Systems Here.