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How Much HP Does a Downpipe Add?

How Much HP Does a Downpipe Add

A downpipe can add up to 10 to 20 horsepower to an engine’s performance – it’s a gain you’ll feel every time hit the accelerator and your turbo spools.

But as with most performance upgrades, you should think of installing a downpipe as part of a larger exhaust upgrade that includes a cold air intake, catback exhaust and tune.

In what follows we’ll take a look at the importance of a downpipe on a turbocharged engine; the difference between a catted and catless downpipe; how it can boost the sound of your ride; as well as how installing an aftermarket downpipe might affect your car’s warranty. Let’s dive in.

How Downpipes Works

Downpipes work with the turbo to deliver more oxygen to your engine.

A downpipe is a unique component to a turbocharged engine – it connects the turbo to the rest of the exhaust system. A turbocharger sucks in air which it then compresses and delivers into the combustion chamber. This higher concentration of oxygen mixes with fuel in the cylinder heads causing greater combustion resulting in more power.

Downpipes are a turbo’s connection to the exhaust system. A downpipe connects to the exhaust side of a turbocharger (more specifically it fits between the turbocharger and catalytic converter). Spent exhaust gases exit the turbocharger through the downpipe. Downpipes are also responsible for reducing backpressure and the temperature of the air the turbo feeds into the engine.

Not only this but downpipes are designed to meet emissions standards often employing components like their own catalytic converters to keep harmful pollutants from entering the atmosphere. But stock downpipes are restrictive.

You Should Consider Aftermarket Downpipes

Aftermarket downpipes are worth the consideration along with other exhaust upgrades for some interesting horsepower gains.

Aftermarket downpipes have a wider diameter than what you get from factory. This girth allows more oxygen to be fed into the engine. Aftermarket downpipes also don’t have as many bends and angles as stock downpipes which restrict air flow thereby choking performance. Most vehicles with a turbocharged internal combustion engine come from the factory with a downpipe.

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The problem is factory downpipes are designed to provide a stock engine with just enough air to meet performance requirements and emissions restrictions. But what’s enough air for your engine changes if your desire is to improve performance. The purpose of installing an aftermarket downpipe is to improve and/or eliminate everything that hampers the flow of oxygen to the turbo. Some of the characteristics of an aftermarket downpipe are fewer bends and a wider diameter. Let’s look at the two different type of aftermarket downpipes:

Catted vs. Catless Downpipes

The difference between catted and catless downpipes means the difference between driving your car legally and not being able to pass emissions.

There are two different types of downpipes. They both help the turbo increase the horsepower of your engine in different ways.

Catted downpipes come with a high-flow catalytic converter. Factory downpipes also come with catalytic converters which work to clean the exhaust gases as they pass through the exhaust system. Upgraded catted downpipes can help the turbo add 15 to 20 horsepower to an engine’s performance. It’s not just horsepower though, you also get more torque out of the deal. Plus, you’ll still be able to pass emissions testing. As we already touched on in the introduction. Adding to your driving engagement, is the fact that a catted downpipe will increase turbo sound. But like with the performance, the change isn’t super noticeable.

Cattless downpipes don’t come with a catalytic converter as you’ve likely already guessed. But are they still worth it? You would think that since there’s even less airflow restriction with a catless downpipe due to the lack of catalytic converter that the horsepower numbers gained would be more impressive. They’re not. You get the same HP figures. But with tuning, you can expect a gain of 50 HP which edges catless downpipes slightly ahead of catted downpipes in terms of sheer performance. The disadvantage here is that there’s no catalytic converter. This means you’re breathing in more noxious fumes which is bad for both you and the environment. And a catless downpipe will result in a check engine in light and numerous codes.

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Downpipes Make Your Car Sound Louder

Along with the appropriate modifications, aftermarket downpipes can make your car sound louder.

Installing an aftermarket downpipe will make your car sound louder and more aggressive. How? Because an aftermarket downpipe is even more efficient than a factory downpipe at reducing backpressure since it doesn’t have as many bends and angles in the design. This allows more sound from both the engine and the flow of exhaust to come through louder and more clearly.

Again, think of this as part of a larger build effort. Swapping your stock exhaust manifold for a high flow performance exhaust along with aftermarket downpipes will go a long way to not only improve the sound quality of your car’s exhaust note. But this combination will also improve performance. While going with a catless downpipe will make your car sound even louder, it will come at a cost.

Your Vehicle’s Warranty Will Be Affected by Installing Aftermarket Downpipes

Before you install that aftermarket downpipe you need to consider how it can affect your vehicle's warranty.

While installing an aftermarket downpipe won’t completely void your warranty, you may lose coverage if anything goes wrong with the rest of the exhaust system. Under the Magnuson Moss Warranty Act, however you have the perfect right to install pretty much any aftermarket part you’d like on your car (within the limits of the law of course).

Just remember that anything that can go wrong likely will go wrong which can limit your coverage. That said, an aftermarket downpipe shouldn’t void your warranty. However, if something goes wrong with your turbo or any other part of your vehicle. It is likely that the dealer will blame it on the addition of an aftermarket part. And on that ground void at least part of your warranty – a failure related to a modification might not be covered by the warranty.

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Other Disadvantages of Downpipes

As with anything else you choose to install on your car, there are some disadvantages that come with upgrading downpipes:

  • For all the benefits of unrestricted airflow, the horsepower gains are marginal. You only start to see a 50 HP increase if you do a tune, which we’ll talk about.
  • Another disadvantage is the smell. Since the exhaust gases are less restricted – whether you go catted or catless – you’re going to notice more of an exhaust smell than with a factory downpipe.
  • You’ll also most likely get a check engine light. Once again, this is where a tune comes in clutch. A tune allows you to change the parameters of the ECU so the check engine light won’t come on.
  • Depending on the state you live in (like California where emissions restrictions are strict), an aftermarket downpipe may be illegal.

Installing Downpipes Require a Tune

To get the most out of your aftermarket downpipe install, you're going to want a tune.

To get every bit of horsepower coming to you after installing new downpipes, you’re going to want to do a tune. Doing this provides a significant horsepower increase to a turbocharged engine. Without a tune, horsepower gains are minimal.

Making the installation of downpipes pretty much worthless. The reason why is because the engine’s software needs an upgrade to take advantage of the higher volume exhaust flow. With a tune after a downpipe upgrade, you’re talking horsepower gains of as much as 100 HP on a smaller engine. And up to double that number on a bigger engine. Of course, these figures also depend on the fuel grade and other engine modifications.

Sources:

Pipsisland.com; Maperformance.com; Roadandtrack.com