
Everything You Need to Know About Exhaust Manifolds
Contents
While internal combustion engines have existed for over a century, the working blueprint (with some modifications) remains the same. Engines produce power by burning an air and fuel mixture to push pistons down and turn crankshafts and wheels. Combustion takes place in a sealed engine block housing the cylinders and engine internals, while spent gases are released through the exhaust manifold and pushed through mid-section tubing and onto the exhaust tips.
Each part plays a significant role. Directly bolted onto the block is the car manifold. This is a single piece or series of welded tubes that collects exhaust gases from the cylinders and directs them to the catalytic converter for treatment (or in turbocharged cars to separate downpipes to power turbines). While most parts are built to a standard and of decent-quality metals, drivers have reported manifold issues, such as decreased power and higher-than-usual fuel use, due to cracks and leaks in the piping. Understanding how these parts work provides a glimpse into the complexities of combustion engines and gives drivers the knowledge to recognise minor issues before they spiral out of control.
What Exhaust Manifolds Are

Exhaust manifolds are the first part of the exhaust system. They’re an integral car component connected to the engine cylinder head and transport waste gases away from the engine, enabling subsequent combustion cycles to take place.
As such, they’re directly involved in engine efficiency, longevity and performance. The component gathers all spent gases, burns off unburnt fuel and gas, and ensures proper airflow within the exhaust system.
Smaller-engined 3 and 4-cylinder cars have a single car manifold, while bigger displacement 6 and 8-cylinder engines have two, one from each cylinder bank.
How They Work
Removing and redirecting waste gases away from the cylinder heads may sound simple, but there’s a lot more going on. The manifold collects spent gases from each cylinder, with high temperatures and pressures pushing exhaust fumes out through the exhaust valves. These go through a series of tubes before being collected into a collector tube. By combining pipes of varying lengths, the manifold helps equalise airflow and prevents the buildup of backpressure, or resistance, ensuring an easy passage towards downpipes or catalytic converters.
There are dozens of variations to manifold designs, differing in pipe lengths, diameters and weld and joint locations. The aim is to streamline airflow out of the car, thereby aiding power. Performance manifold or sport headers are optional upgrade parts that help with torque and horsepower when combined with similar performance parts like cold air intakes. Both components deal with airflow; air intake with atmospheric air drawn in for combustion, and manifolds and headers with spent gases that need to be removed as quickly as possible.
Design Specifics
Depending on the intended purpose and the engines they appear in, exhaust manifolds come in two basic types – cast and tubular. Cast manifolds are made of a single piece of metal cast into a mould to achieve the final shape. They’re what you’d find in most production models. The downsides are the uniform tubing length that impedes airflow and creates restrictions, their higher weight and that they rob the engine of power. They’re widespread due to low production costs but are bettered by tubular designs (or sport headers) in almost every aspect.
These have individual pipes extending from each cylinder, often in different lengths to balance pressure and temperatures from cylinders firing in different sequences. They’re also recognisable by their designs, with 4-2-1 and 4-in-1 piping configurations common in performance vehicles where they help with mid-range torque and reducing backpressure with improved airflow. Additional benefits are lower weight and materials more suitable for higher engine loads with increased heat and pressure.
Materials Used in Manifold Production

Cast iron, aluminium, stainless steel and titanium are the most common materials. Cast iron types are preferred for their high heat loading, decent durability for most uses, and low production costs. The material is relatively heavy compared to other options, can suffer under higher engine loads, and is known to be brittle and crack with increased pressure.
Choose an aluminium car manifold if you’re after low weight, high strength and unmatched corrosion resistance for the price. The material is also malleable and machinable, especially for tubular designs and is now the standard in most new cars. Another viable alternative is stainless steel. Manifolds made with this material are durable, resistant to rust, and cope with higher temperatures and pressure generated in bigger and more powerful engines. Like aluminium, stainless steel is also machineable, so is suitable for performance or custom manifolds, but typically requires more work, often leading to higher prices.
Lastly, choose titanium if you’re after high-performance exhaust manifolds. The material is lighter than aluminium, tougher than steel and has better heat and corrosion resistance than both. These properties though come at a price and you’ll find titanium in one-off builds or exclusively in racing applications.
When to Look for a Replacement?
Cracks, dents and leaks due to metal fatigue, high heat, pressure, corrosion or a combination of all four are when you’ll need repairs or a new unit. Typical signs are hissing, tapping or vibrating noises, reduced performance including poor acceleration and high fuel consumption, and noticeable smells leaking into the engine.
While it’s possible to continue driving with a damaged exhaust manifold, you risk damage to engine parts like exhaust valves, camshafts and injectors due to the ECU overcompensating for leaks with higher fuel spray (leading to rich fuel mixtures, off timing and black smoke) and damage to all exhaust systems components, including oxygen sensors.
To prevent further damage, decide if the unit can be fixed with welding or if it needs replacing. Shop for manifolds compatible with your engine, or go with upgrades from established brands if you’re rebuilding or modifying your car for more power.