What is a downpipe and why do I need one?

What is a downpipe?

Are you looking to add more power to your vehicle? If your vehicle is equipped with a turbocharger, a downpipe may be part of your solution. The downpipe bolts directly to the turbine housing and helps direct exhaust gases through the rest of the exhaust system. Most factory downpipes will have at least one very restrictive catalytic converter. These do a great job of cleaning the exhaust gases but are also very restrictive causing potential power to be lost.

CTS Turbo 3.5" Downpipe - w/o Cat (15+ A3, 15+ GTI/Golf) - CTS-EXH-DP-0014

The CTS Turbo 3.5″ Catless Downpipe for MK7 GTI, Golf and the 8V A3 is a popular choice for front wheel drive MQB VW and Audi vehicles.

What does a downpipe do?

The downpipe on your turbocharged vehicle is directing the exhaust gases out of the turbine housing into the exhaust system. An aftermarket downpipe will typically be larger in diameter and either uses a high-flowing catalytic converter or remove the catalytic converter altogether.

By removing the factory downpipe and replacing it with a high flowing unit you are allowing the turbo to more efficiently move gases away from the turbine which creates more power. Since the factory restrictions are now gone you can increase the boost on the vehicle as the factory downpipe is a choking point for performance.

Why do I need one?

The biggest bang for the buck will come from an ECU tune and a downpipe. If you are looking to make the most power from your stock turbo, a downpipe is a critical piece of the puzzle. The downpipe paves the way for Stage 2 power levels.

What does it mean when I see (cat vs catless)?

Aftermarket downpipes typically come in two configurations. One being catted (with high-flow catalytic converter) and the other being catless(all the catalytic converters are removed). The catalytic converter cleans the exhaust gases as they pass through the catalyst. This means you will not have to worry about the smell of raw exhaust fumes. If you purchase a catless downpipe be aware that the vehicle is going to smell as those exhaust gases are not being cleaned prior to exiting the vehicle.

DFG Tuning 3" Downpipe w/Cat (15+ A3, 15+ GTI/Golf) - DFG-70003-CAT

Here you can see the catalytic converter on the DFG Tuning 3″ Catted Downpipe (15+ 8V A3, 15+ MK7 GTI/Golf).

What do I need with a downpipe to make it work?

On most Audi & Volkswagens you will need what people refer to as a “stage 2” tune. This means that the computer has been modified to a. Produce more power now that a downpipe is installed b. Recalibrate the O2 sensor so it does not throw a catalyst inefficiency code. If you install a downpipe on a vehicle and don’t have the proper software you will get a check engine light for this reason.

Is it street legal?

The short answer is NO. Modifying the factory emission systems automatically guarantees you will not pass local or state emissions. Even if you have a high-flow catalytic converter some states may not pass the vehicle as it is not the OEM unit. This is not the case for every state but it is very important to know the laws of your state or county prior to installing an aftermarket downpipe.

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