Headers vs. Exhaust Manifolds: How Do They Affect Performance? – Jalopnik

Upgrading the exhaust is one of the first steps many take when looking to improve the performance of their car. One of the most obvious choices in this regard is to install a header in place of the stock exhaust manifold, which will certainly give your vehicle a little more oomph. But manifolds have their own thing to do.

An exhaust manifold is the starting point of the exhaust system and its job is simple: it collects spent gases from each cylinder and directs them to the rest of the exhaust system. However, a lot is asked of it in other areas. It must thanklessly do its job year after year with minimal maintenance, fit reliably into tight spaces, bear the brunt of constant heat cycles, and do it all silently. Manufacturers take all of this into account when designing a manifold, and most factory versions are made of cast iron (which Dodge and Ram still use to make their engine blocks) or stainless steel. They fit easily into tight engine bays and can withstand whatever the vehicle throws at them.

Headers are an important upgrade for drivers who want more from their engine without major internal work. Simply put, headers replace the stock exhaust manifold with individual pipes for each cylinder, allowing exhaust gases to escape more efficiently. By improving airflow and reducing back pressure, headers help your engine breathe better, supporting stronger performance and better throttle response.

In a manifold, the exhaust from each port is often vented into a single chamber or short channels, so the interaction between the exhaust pulses from different cylinders is rapid. While this softens much of the noise associated with exhausts, it can also create back pressure. Back pressure is the pressure buildup and resistance created in the exhaust system that opposes the flow of exhaust gases leaving an engine. This poses a problem because to push the exhaust gases out against this pressure, the pistons have to work harder, causing a loss of efficiency.

Headers take a different approach. Each cylinder gets a separate tube and the exhaust gases leave the tubes before joining a collector, rather than coming together immediately. The use of individual tubes also means that the length of each tube can be adjusted, controlling how the pulses flow together and reducing back pressure.

Headers with different tube lengths are called unequal headers. By having pipes of unequal lengths, they can spread torque delivery across different rpm ranges and create a smoother, broader powerband. This header design is also what makes Subarus so unique. Equal-length headers use pipes cut to the same length so that the exhaust pulses reach the collector evenly, allowing the power to be sharpened over a narrower rpm range.

The performance difference between headers and exhaust manifolds is real, but not universal. Headers generally produce more horsepower and torque by improving exhaust flow. They also help remove exhaust gases, especially during the short period when both the exhaust and intake valves are open at the same time. When an exhaust pulse flows through a collector tube, a low-pressure area is created behind it. If the timing is correct, that low pressure helps pull the remaining exhaust gases out of the cylinder and allows the incoming air-fuel charge to come in more efficiently.

That said, the winnings are highly dependent on the rest of the combination. On a near-stock engine with a restrictive downstream exhaust, the improvement may be modest. With a well-tuned setup with good intake flow and a free-flowing exhaust, the benefits are easier to measure and feel.

Manifolds, on the other hand, excel in areas that don’t show up on a test bench. They are resistant to warping and cracking. Installation is usually simpler and heat management is usually more predictable.

Sound also plays a role in the decision. Headers retain sharper exhaust pulses for longer, resulting in a more aggressive tone. Manifolds blend these pulses sooner, creating a deeper and more subdued sound. But whether you use manifolds or headers, a cheap exhaust sounds terrible.