How Different Downpipes Work

How Different Downpipes Work

Last Updated August 4, 2019 | Meghan Drummond

On turbocharged vehicles, like the Mustang EcoBoost, a downpipe is what carries exhaust gases from the turbine housing to the rest of the exhaust system. Downpipes can also refer to the tubing in older cars that runs straight from the exhaust manifold to the rest of the exhaust. Aftermarket downpipes are available that can further improve performance, but it’s important to note that not all of these modifications may be legal in your state.

Factory Downpipes

Your EcoBoost Mustang came with a stock downpipe equipped with a catalytic converter. Catalytic converters run exhaust gas through a honeycomb that’s coated in rare metals like platinum and palladium. These metals act as a catalyst, and re-burn your exhaust fumes, allowing fewer harmful gases to exit.

This is a good feature, nitrous dioxide, in particular, has been linked to a significantly increased risk of lung cancer, but it can make your vehicle less powerful as well.

Like many factory parts, the standard catalytic converter isn’t necessarily the best functioning cat available; it’s a model that is used for many different vehicles and is designed to more or less meet the needs of all of those vehicles. When upgrading, there are aftermarket downpipes that include a better catalytic converter as well as downpipes that eliminate the catalytic converter entirely.

A stock downpipe and an aftermarket one lay beside each other

Aftermarket Downpipes with Catalytic Converters

Aftermarket downpipes often come with high-flow catalytic converters installed. These are designed to impede the flow of exhaust fumes less than the stock catalytic converter does and will work with your specific vehicle more efficiently.

Catted downpipes offer a solution that cleans exhaust fumes and keeps your horsepower intact. It’s impossible to estimate exact horsepower gains, but consistently owners report seeing up 20 rear wheel horsepower increases, which is definitely substantial.

Because states have different restrictions for aftermarket catalytic converters, you should check your individual state’s requirements before purchasing an aftermarket downpipe. You may also need a tune following installation because it is likely that you’ll see a “check engine” light come on after installation. That’s normal and easily cleared, but if it’s not removed before your vehicle’s emission inspection it is likely that it won’t pass.

A braided steel section of a pipe where the cat is

Off-Road Downpipes

Off-road downpipes, true to their name, are only legal for off-road performance. If you have a performance vehicle that only ever sees track use, then these downpipes show the largest performance gains and change the sound of the exhaust to a rumble so deep your neighbors will certainly be upset if you ever do try to drive it on the street.

By removing the catalytic converter entirely off-road downpipes are able to offer a completely unrestricted exhaust flow. This is not street-legal in any state and if you are caught with it even in a state without emissions testing you will get a ticket, fortunately, they don’t issue emissions tickets on the track.

Without the catalytic converter, there is nothing stopping the exhaust fumes from affecting you either, so it’s important to try to limit your exposure or wear protective equipment to prevent yourself from inhaling unfiltered exhaust.

Installing an Aftermarket Downpipe

Installing a downpipe is relatively easy, the most challenging part is ensuring that everything is properly replaced and installed, including the 02 sensors. In this CJ’s video, Bill shows us how to do a basic downpipe install.

If you have a turbo engine, then upgrading your downpipe is an easy way to see big performance increases with relatively minimal effort. By ensuring that your downpipe is legal in your state, you can also avoid tickets.

With a variety of aftermarket downpipes available, one of the easiest ways to narrow down your options is to think about where you think you’ll be using your Mustang most often. If you’re frequently driving on streets or around people, then buying a catted downpipe will give you a healthy mix of safe to breathe air and performance boosts.

But a non-catted downpipe will provide the surest performance boosts, and if you’re only breathing in the fumes one or two days a week you’ll be unlikely to notice any substantial health concerns.

How Different Downpipes Work

Downpipes are an important part of a turbocharged vehicle's exhaust system Aftermarket downpipes can improve performance, but may or may not be legal in your state. There are a lot of different options for downpipes, and here's what you should know about each of them, including legality and safety.