Secondary Downpipes BMW XM G09

1. AXI Performance Catted Downpipes (With High-Flow Catalytic Converters)
Design:
AXI Performance's catted downpipes use a high-flow catalytic converter, which is designed to be less restrictive than OEM cats while still reducing harmful emissions.
These high-flow cats allow for a better exhaust flow, which improves performance compared to stock downpipes.

Performance:
High-flow catalytic converters in AXI’s catted downpipes are engineered to increase power by reducing backpressure compared to OEM downpipes. This leads to better turbo spool, more efficient exhaust flow, and increased horsepower and torque.
The power increase is generally moderate, but it's noticeable when compared to stock setups.

Emissions:
Catted downpipes still provide some level of emissions control, making them legal in areas with emissions testing requirements (depending on local laws).
They won't be as clean as OEM catalysts but are designed to strike a balance between performance and emissions.

Sound:
Expect a more aggressive sound compared to stock downpipes. It's louder and deeper, but not as extreme as catless downpipes.
The high-flow cats still somewhat reduce exhaust noise, but the overall sound will be much more pronounced than OEM.

2. AXI Performance Catless Downpipes (Without Catalytic Converters)
Design:
Catless downpipes from AXI Performance completely remove the catalytic converter, allowing for the maximum possible exhaust flow.

This results in a direct path for exhaust gases, with no restriction from catalytic filtration.

Performance:
This setup provides the biggest performance gains, especially in turbocharged vehicles. Without any cats in the way, the exhaust flow is maximized, which leads to significant improvements in horsepower, torque, and throttle response.
Turbo spool time is quicker due to reduced backpressure, allowing the turbo to operate more efficiently.

Emissions:
No emissions control with catless downpipes, which makes them illegal in most areas with emissions laws.
In addition, catless downpipes will trigger a check engine light (CEL) due to missing O2 sensors or no catalytic converter.

Sound:
Expect a loud, aggressive exhaust tone. With no catalyst to muffle the sound, it will be significantly louder and more raspy than stock or catted setups.

3. Original Catalysts (OEM Catalytic Converters)
Design: These are factory-installed catalytic converters in your vehicle's exhaust system. They are designed to meet the required emissions standards for road use and are usually very restrictive to ensure they trap as many harmful particles as possible.

Performance:
OEM cats are designed to be emission-compliant rather than optimized for performance.
They create more backpressure, which can limit power and throttle response.
This means stock Catalytic Converters generally result in less power output compared to high-flow aftermarket downpipes.

Emissions:
The main purpose of stock catalytic converters is to reduce pollutants (carbon monoxide, hydrocarbons, nitrogen oxides, etc.).
They're highly restrictive to capture these pollutants but ensure that the car passes emission testing.

Sound:
OEM catalysts are relatively quiet, and they help reduce exhaust noise, keeping it within legal limits.

Final Thoughts:
If you're looking for better performance but still need emissions compliance, AXI Performance’s catted downpipes are the better choice.

For maximum performance gains and if emissions are not a concern, catless downpipes are the best choice, but be aware of potential legal issues and sound levels.

Original catalysts are fine if you want to keep things stock, but expect limited performance improvements and higher restrictions in terms of exhaust flow.

When upgrading a turbocharged vehicle, one of the most effective modifications is replacing the factory downpipe. This change can unlock horsepower, improve turbo response, and enhance overall driving performance. However, a key decision must be made: should you install a catted or catless downpipe? Each has its own advantages, drawbacks, and best-use scenarios.

What Is a Downpipe?
A downpipe is a section of piping that connects the turbocharger to the rest of the exhaust system. AXI Performance downpipes are designed to reduce restriction and improve performance. They come in two main forms: catted and catless.

Catted Downpipe
A catted downpipe includes a high-flow catalytic converter. This allows for better performance than the stock unit while still helping reduce harmful emissions.

Pros:
Legal for street use in many areas;
Reduces or prevents check engine lights (CEL);
Less exhaust odor compared to catless downpipes;
Better environmental impact than catless downpipes;

Cons:
More restrictive than a catless downpipe;
Generally more expensive;
May still require tuning to avoid CEL on some vehicles;

Catless Downpipe
A catless downpipe removes the catalytic converter entirely to maximize exhaust flow.

Pros:
Highest possible horsepower and torque gains;
Faster turbo spool and reduced lag;
Less expensive;
Ideal for race or off-road vehicles;

Cons:
Not emissions compliant in most regions;
Strong fuel or exhaust odor;
Likely to trigger a CEL without proper tuning;
Illegal for public road use in many areas;

Catted vs. Catless: Which Should You Choose?
Choosing between a catted and catless downpipe comes down to your goals, driving habits, and local regulations. Both can provide performance benefits, especially when paired with a proper ECU tune. For most street-driven vehicles, a high-flow catted downpipe is the safest and most practical upgrade. For pure performance builds, catless may be worth the tradeoffs.

Does the AXI Performance Downpipe Increase HP?

One of the most significant benefits of upgrading to a performance downpipe, such as the AXI Performance downpipe, is improved exhaust flow. The downpipe (catless or catted) is designed to be less restrictive compared to the stock catalyst. With better exhaust flow, the engine can expel gases more efficiently, which means the engine doesn’t have to work as hard to get rid of the exhaust. This improvement in efficiency directly lead to increased horsepower.

• Reduced Turbo Lag:
• For turbocharged engines, one of the key factors in improving performance is reducing turbo lag. Turbo lag occurs when the turbocharger takes time to spool up and deliver more power. A restrictive original catalyst can exacerbate turbo lag by limiting the exhaust flow that’s needed to spin the turbo. By installing a performance downpipe, such as the AXI Performance downpipe, exhaust gases can flow more freely, reducing turbo lag and allowing the turbo to spool up faster. This means the engine will respond more quickly to throttle inputs and generate power sooner, which contributes to a noticeable increase in horsepower.
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• Increased Boost Efficiency:
• The more freely exhaust gases can flow through the system, the more efficient your turbo system will be at generating boost. With an upgraded downpipe, such as the AXI Performance downpipe, the turbocharger doesn’t have to work as hard to produce the same level of boost. This increased boost efficiency can directly impact the amount of horsepower produced by the engine, often resulting in a gain of anywhere from 10 to 30 horsepower, depending on the vehicle and other supporting modifications.
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• Supporting Modifications:

  It's important to note that a downpipe alone may not provide the largest horsepower increase. For maximum gains, it's typically recommended to pair a performance downpipe with other supporting modifications, such as:

ECU Tuning: After installing a performance downpipe, a proper ECU soft tune is often required to adjust the engine management system for the increased exhaust flow, ensuring optimal performance (stage2).

Upgraded Turbo: If you're looking for even more substantial power gains, an upgraded turbocharger can be paired with a performance downpipe to fully unleash the car's potential.

Power Gains – What to Expect:
With a well-designed downpipe like the AXI Performance downpipe, you can expect noticeable power gains.

For most turbocharged vehicles, the gains will typically range up to 30 horsepower, depending on the car’s model, engine, and existing modifications. On a BMW B48 2.0L turbo engine, for instance, you might see an increase of around 20 hp just from the AXI Performance downpipe alone. However, the exact gains will vary based on several factors, including whether your car already has performance modifications in place or if it's running a stock setup.