Monday, November 17, 2014
What Is Between the Catalytic Exhaust Manifold
Catalytic converters, also called "cats," absorb exhaust heat, and should, ideally, be as close as possible to the exhaust manifold for emissions compliance. This placement varies by make and model and can have a significant impact on performance.
The Y-Pipe
V-type engines often use y-shaped pieces of tubing to join the cylinder banks exhaust streams before entering into the converter. Converters are often bolted right to the back of this Y-pipe.
Direct Connection
Many manufacturers, such as Honda and Toyota, are becoming known for bolting the catalytic converters right to the exhaust manifold outlet, with nothing in between.
Down Tubes
Most turbocharged engines use a down tube, which is a smooth piece of tubing that allows a turbos exhaust flow to move away smoothly, before encountering the restrictive cat.
Oxygen Sensor
All new vehicles have an oxygen (O2) sensor somewhere between the exhaust manifold and cat. This works in conjunction with an after-cat O2 sensor to notify the engine control computer of any converter malfunction.
Exhaust Brakes
Large diesel trucks often have a large valve in between the cat and manifold, known as an exhaust or "Jacobs" brake. When closed, these valves create back pressure in the engine and allow a driver to control downhill acceleration without using the foot brake.
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