Last days of exhaust pipe

It wasn’t so long ago that the pipes used to remove the combustion products leaving the engine were one of the main pillars of increasing the performance of passenger cars. It will remain so for a few years, but more than likely the days of this component group are numbered.

However, as long as internal combustion engines exist, this seems to be insignificant element will play a crucial role in the operation of vehicles. This role is presented in the following article. 

Criteria

Both gasoline and diesel vehicles produce significant waste heat during the combustion process. A significant part of this leaves through the exhaust, in the form of numerous compounds.

The exhaust pipe must be carefully designed so that the flow of gases is as smooth as possible. The lower the resistance of the system, the fewer obstacles the flowing gas encounters, thereby increasing the ability to flush the engine – in other words, the power output of the resource.

In addition, safety is also an important factor; the pipe must be heat resistant and must not pass through or be close to any object that can be burned or damaged by heat.

Downpipe

In most production engines, the downpipe is an assembly that collects the exhaust gases from two or more cylinders into one pipe. In stock cars, downspouts are often made of cast iron and may have material-saving design features such as using the least amount of metal, taking up the least amount of space, or having the lowest manufacturing cost. These design limitations often result in a design that is cost effective but does not do the most efficient job of exhausting gases from the engine.

Exhaust system developed for racing purposes (source: www.wikipedia.org)

The lack of efficiency is usually due to the nature of the internal combustion engine and its cylinders. Because the cylinders fire at different times, the exhaust gas leaves them at different times and the pressure waves from the gas leaving one cylinder may not completely exit the exhaust system when another cylinder takes its turn. This creates back pressure and restriction in the engine’s exhaust system which can mask the engine’s true performance.

A common method of increasing engine performance is to use improved downpipes. The reason for the increased performance is often due to the larger cross-section of the pipes (reducing the resistance of the exhaust gases) and/or the design of the pipe lengths in such a way that the pressure wave helps the exhaust gas drainage. Exhaust manifolds on inline-fours and V8s are usually either a 4-2-1 design (where the four pipes are combined into two sections and then these two pipes are separately combined into one) or a 4-1 design (where the four pipes join directly).

Downpipes are usually made by aftermarket companies but can sometimes be purchased from high-performance parts departments at auto dealerships.

Catalyst

The main purpose of a car’s catalytic converter is to reduce harmful emissions of hydrocarbons, carbon monoxide and nitrogen oxides into the atmosphere. They work by converting polluted exhaust gas components into water and carbon dioxide. There is a switching temperature above which catalytic converters are efficient and work properly.

Catalysts can cause back pressure if they are not designed for the required flow rate or if they are clogged. In such situations, upgrading or removing the catalytic converter can increase performance at high rpm. However, the catalytic converter is a key component of the vehicle’s emissions control system so a non-standard product can make the vehicle unroadworthy.

Exhaust pipe

The pipes connecting individual components of the exhaust system are called exhaust pipes. If the diameter is too small, the performance will decrease at high speed. A diameter that is too large can reduce low-rpm torque and push the tailpipe closer to the ground, increasing the risk of knocking and damaging the car while it is moving.

On cars equipped with two exhaust pipes, a cross pipe is often used to connect the two pipes. The common design of cross tubes is a perpendicular tube (“H-tube”, due to their shape) or angled tubes that join and separate diagonally (“X-tube”).

Muffler

Original mufflers generally reduce pipe noise by bouncing sound waves off the back, front, and sides of the exhaust. They are designed to meet the maximum allowable noise level required by government regulation, however some original equipment mufflers are a significant source of back pressure.

C7 Corvette with 4 exhaust manifolds (source: www.wikipedia.org)

Bottle mufflers (also known as “cannons” or “hotdogs”) are straight design mufflers consisting of an inner perforated tube, an outer solid tube, and fiberglass sound insulation between the two tubes. They often have less back pressure than the original mufflers, but are not effective in reducing noise levels. Another common type of silencer is the chamber silencer, which consists of a series of concentric or eccentric tubes in the cavity of an expansion chamber. These tubes allow sound to enter and bounce the sound waves off the closed, flat ends of the tube. These reflections partially cancel each other, reducing the sound level.

Resonators are sections of pipe that expand to a larger diameter and allow sound waves to bounce off the walls and cancel them out, thereby reducing the noise level. Resonators can be used inside mufflers or as separate elements of the exhaust system.

In trucks, it is possible that the silencer is crossed under the front of the cab and the exhaust pipe blows sideways (right side if you drive on the left side, left side if you drive on the right side). The side of a car where the exhaust exits under the rear bumper usually indicates the market the vehicle was designed for, so Japanese (and some older British) vehicles have a right-hand exhaust, so those countries are farthest from the curbside where drive on the left, while European vehicles have exhausts on the left.

The end of the final length of the tailpipe, where the gases escape is usually the only visible part of the exhaust system component in the vehicle, often ending in a straight or beveled cut, but may also include a decorative exhaust manifold. It often consists of a larger pipe than the rest of the exhaust system. This results in a final pressure drop and is sometimes used to improve the appearance of the car.