Do Exhaust Headers Add Horsepower?

When it’s time to start upgrading to a performance exhaust system, it’s easy to get enamored with a throaty rumble coming from shiny exhaust tips.

But if you’re chasing horsepower, don’t overlook a good set of performance headers.

Given that’s where the exhaust gasses begin their journey, that notion may be obvious—but not many gearheads really dig into the science of why. We’ll explain it all in a bit more detail by addressing this question:

How Do Headers Add Horsepower?

Think of your engine as a big, fancy air pump. The more air it can move in and out, the better it will perform.

Admittedly, we use this analogy a lot, but it’s particularly apt here. When many folks think about engine airflow, they often stop the journey once they make it to the combustion chamber—but that’s just where the party begins. After that, the engine has to expel all those spent exhaust gasses and, then of course, pull new air in; lather, rinse, and repeat.

A good set of headers allows the gasses from each cylinder to exit the engine more efficiently, passing down a smoothly transitioned primary tube before mixing with the exhaust from the other adjacent cylinders.

This is in contrast to a stock manifold that may have a rough casting finish that can restrict flow and, more importantly, a design that forces the exhaust gasses from each cylinder to mix almost immediately upon leaving the engine.

As an added benefit, a good header design takes advantage of the scavenging effect—it can actually help pull a fresh air/fuel mixture into the cylinder head.

Since exhaust gases escape the cylinder very quickly, the high-speed pulse moves down the header tube and creates a low pressure spot behind the initial pulse. The resulting low pressure vacuum helps draw new air back into the engine. Want a more elaborate explanation? Read this: Exhaust Scavenging, Explained

So, Do Headers Add Horsepower?

For the answer, we turn to our pal and OnAllCylinders contributor Richard Holdener—he’s logged more dyno time than any human we know, and better still, he documents all of his finds in brilliant tech articles and videos.

Let’s start with this article he penned for EngineLabs: Cast Manifolds Vs. Tubular Race Headers. Here he’s testing a turbocharged LS using a set of OE-style cast manifolds from Hooker against a full set of race headers. Granted, this is a bit more ambitious than swapping out the manifolds on your daily driver, but the results speak for themselves:

But one series of dyno pulls doesn’t make it the truth. To that end, Richard Holdener also has some other tests that support the horsepower benefits of adding headers. You can check those out on the Richard Holdener YouTube Channel using the links below:

• How to Improve 8.1L Power: Stock Manifolds vs. Headers
• Do Long Tube Headers Add HP?
• High HP LS Header Test

Obviously most of these tests are run with other performance upgrades and power adders, but given the consistency of the results, it’s fair to say that headers do add horsepower.

Now the question remains…

How Much Horsepower Do Headers Add?

It depends. Which we know isn’t the greatest answer—but there about a thousand other variables that impact the output of an engine, including both the weather and elevation during the dyno test.

But more directly, you’ve got to consider heads as merely part of a broader picture. Just like an air intake kit, adding a set of headers alone may not move the HP needle all that far.

The magic lies in compounding numbers—headers by themselves produce modest gains. But combine headers with a full cat-back performance exhaust system, a cold air intake kit, and a pair of performance cylinder heads and you’ll really see the benefit.

The overall goal here is to ensure your engine’s flow (both intake air and exhaust gas) is free of potential choke points that could inhibit performance.

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Performance exhaust technology is a complex, nuanced topic—so we’ve put together some more articles on related subjects to help you out. If you really want to go down the rabbit hole of exhaust system performance, give these posts a read too:

• Will These Exhaust Headers Fit my Vehicle?
• A Beginner’s Guide to Aftermarket Exhaust Systems
• How To Choose an Aftermarket Exhaust System
• An Introduction to Exhaust System Components
• How Does an Exhaust Pipe Affect Engine Performance?
• How Much Horsepower Does a Dual Exhaust Add?
• What is the Purpose of a Crossover Pipe on an Exhaust?