Exhaust Systems and Air-Fuel Controllers Explained
Where does the exhaust gas go and how can we extract the most from the system? Welcome to the second installation of Automotive News. In the first, we talked about the intake system and exhaust headers and how to get more juice from your car's engine.
The exhaust header is the first component of an exhaust system and this month, we will cover the remaining parts of the system and some basic tuning gadgets. After the exhaust header, the pipes meet at a "collector" which ends with a flange, allowing it to be bolted to the rest of the exhaust system.
Here, it usually meets the catalytic converter which reduces the toxicity of exhaust emissions by passing them over a honeycomb of precious metals that turn noxious emissions into carbon dioxide and water vapour. With such an important role, catalytic converters, though mildly restrictive to the flow of exhaust gases, are usually left in place by drivers.
You may have heard the term "cat-back" system when shopping for an aftermarket exhaust system. This refers to the remaining exhaust components that are found after the catalytic converter, usually consisting of more exhaust piping that end with the muffler box and tip. These let you drastically change how your automobile performs and sounds.
Aftermarket cat-back systems work on principles similar to performance headers. They're less restrictive and the reduction in backpressure means less force required to expel exhaust gases. And if a cat-back system is sufficiently free-flowing, it helps the engine to take fresh air in - the same way exhaling freely helps you take nice deep breaths.
But if there's more air going into (and out of) your car's engine, the increase in oxygen would have to figure in the engine computer's calculations when it signals the fuel injectors, so that every cylinder gets just enough fuel.
The factory ECU (the "brain" of your automobile) calculates the fuel-to-air ratio for an unmodified engine, but introducing basic modifications might require an adjustment in the amount of fuel injected. This is where an air-fuel controller comes in handy as it allows a technician to fine-tune air-fuel ratios, providing the engine with the precise amount of fuel needed for the larger amount of air fed to the engine.
By tapping onto the signal of the automobile's airflow/pressure sensor (which measures the amount of air moving through the engine's intake system), corrections to the air-fuel mixture can be performed across the RPM range. For a smoother power band and maximised use of aftermarket parts' capabilities, all you need is proper tuning. Handy displays also allow users to monitor engine statistics such RPM and throttle position. With these three basic modifications (intake, header and exhaust), a complementary air-fuel controller usually increases the performance of your automobile and makes your ride a more enjoyable one.
This article is written by Leow Julen, contributing writer for Top Gear Singapore, and Samuel Kang, editor for Rev magazine.