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What Is an EcoBoost Mustang's Downpipe and What Does it Do?

Shop EcoBoost Downpipes

All turbos lead to downpipes, and as you can imagine there's plenty of power to be scavenged from one pipe. The aftermarket has been quick to provide with on-road and off-road options.

Shop Downpipes

It's been a while since we've a turbocharged Mustang, and other technology has changed, the components are familiar. You can alter your EcoBoost's attitude by changing out one pipe: the downpipe.

American Muscle

What is a Downpipe?

A downpipe is the section of your exhaust that runs from your exhaust manifold to your catback. The factory catalytic converter is integrated into the downpipe. This section of exhaust is equivalent to the H pipe or X pipe found on GT and 11 V6 Mustangs, or the Y pipe found on older V6 Mustangs. Upgrading this portion of your exhaust will result in better flow and more horsepower. They come in two different styles, off-road or catted. The off-road downpipes provide better flow, but will not pass emissions testing.

Why Should I Upgrade My Downpipe?

As you modify your EcoBoost Mustang, you will surely be ramping up your boost. With the increased boost, you’ll have even more exhaust gasses fighting to get out. Even with a completely stock engine, the factory downpipe is restrictive and will rob you of horsepower. Deleting the catalytic converter or replacing it with high flow converter will result in more horsepower over the factory catalytic converter, allowing your modified Mustang to breathe a lot better.

Since the turbocharger is essentially a pump, it is important the pipes entering and exiting the turbocharger are free from restriction. The stock downpipe usually has many bends which creates pressure within the system. By reducing the amount of restriction, the turbocharger can spool up more quickly. A faster spool-up time will increase efficiency in power and fuel economy.

S550 EcoBoost Downpipe Air Flow Diagram

Off-road Downpipe

If you have ever installed an off-road downpipe or mid pipe before, you know that they drastically increase the volume of your Mustang. Without the catalytic converters on the car, you will also notice the smell of raw fuel. If you do not mind having a really loud Mustang and excess fuel smell, you will want to go with an off-road downpipe for the most horsepower gains. You can still get a ticket for removing your catalytic converter in states without emissions testing, so keep that in mind when making your choice!

2015 Ecoboost Downpipe

Catted Downpipe

For those of you that live in states with emissions testing, you will want to install a catted downpipe. This will allow you to pick up most of the gains of an off-road downpipe, while still keeping your Mustang emissions compliant. In states with California emissions standards aftermarket catted downpipes may not be legal. You will need to check with your local testing agency before ordering your downpipe if you need a downpipe that is California compliant. Even if you do not live in an emissions restrictive state, a catted downpipe is perfect for Mustang owners that do not want the increased exhaust volume and fuel smell associated with an off-road downpipe.

What Gains Will I See With an Upgraded Downpipe?

Installing an off-road downpipe on your Mustang will give you a gain of around 20-25 rear wheel horsepower if you already have a custom tune. You will gain even more power on a stock Mustang if you load a custom tune while installing your downpipe. For those of you that choose to go the catted route, you can expect to see about 5 RWHP less than an off-road downpipe, since the high flow catalytic converter will still restrict your exhaust a little bit.

Ecoboost Dyno Test

Which One Should I Choose?

Catted Downpipe:

  • Live in an emissions restrictive state
  • Want to keep your exhaust volume quiet
  • Do not want excess fuel smell
  • Do not want to risk getting a ticket

Off-road Downpipe:

  • Do not live in an emissions restrictive state
  • Want a loud exhaust
  • Do not mind excess fuel smell
  • Are not worried about getting a ticket
  • Looking for maximum power gains

Legality around Aftermarket Downpipes

Changing downpipes can affect the passing of inspection/emissions in certain states. If your state tests for catalytic converters, swapping to an off road downpipe can be cause for failure to pass inspection. On the other hand, aftermarket catted downpipes can still pass provided one is not in California. In California, changing the downpipe or modifying in any way is prohibited and will not pass inspection.

Fitment includes: 2015, 2016, 2017, 2018, EcoBoost