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Choosing the right exhaust upgrade for your vehicle can feel overwhelming. Headers and high-flow catalytic converters each serve distinct purposes, and understanding their differences is crucial for making an informed decision that aligns with your performance goals and legal obligations.
Headers are designed to maximize power output and deliver a more aggressive exhaust note. High-flow catalytic converters, on the other hand, aim to reduce emissions while minimizing power loss. If you’re chasing substantial horsepower gains and a throatier sound, headers typically deliver better results. But if maintaining emissions compliance and passing inspections is your priority, high-flow cats offer a safer, more street-legal solution.
This article explores what headers and high-flow catalytic converters actually do, how they impact your vehicle’s power and sound, and what they mean for emissions compliance. By the end, you’ll have a clear understanding of which upgrade—or combination of upgrades—best suits your needs.
What Are Exhaust Headers?
Headers replace your factory exhaust manifold with individual tubes that guide exhaust gases away from each cylinder more efficiently. Headers have a tube construction with one tube for each exhaust port, and both meet in a large tube, also known as the collector.
Headers add horsepower by reducing restrictions and supporting scavenging. These components accelerate the flow of exhaust gases and create less back-pressure on the manifolds. By allowing exhaust gases to exit more freely, headers help your engine breathe better, which translates to improved performance.
There are two main types of headers: long-tube and short-tube (shorty) headers. Long-tube headers make their power in the mid- to high-RPM range and are superior to both stock and most aftermarket shorty headers. If you can get long-tube headers to fit, you’ll usually realize the most power gains.
Short tube headers improve low-end torque, making them a solid choice for daily driving or towing. For those looking for extra power without sacrificing drivability, short tube headers are a great option. Shorty headers are also easier to install and typically work with your existing exhaust system.
Aftermarket headers can be catless or catted. Catless headers eliminate the catalytic converter entirely, which can provide maximum flow but will almost certainly cause emissions compliance issues. Catted headers include integrated catalytic converters, offering a compromise between performance and legality.
What Are High-Flow Catalytic Converters?
A high-flow catalytic converter is designed to perform the same emissions-cleaning role as a standard catalytic converter but with far fewer restrictions to exhaust flow. Unlike gutted cats or test pipes, high-flow cats retain emissions controls while allowing exhaust gases to pass through more easily.
By using advanced materials and construction techniques, high-flow cats allow exhaust gases to pass through more freely, improving the overall efficiency of the exhaust system and boosting engine performance. Unlike standard converters, which are optimised for emissions at the cost of performance, high-flow catalytic converters strike a balance between environmental responsibility and power output.
The key difference lies in the internal structure. CPSI is the acronymn for cells per square inch. So therefore 400CPSI, 300CPSI, 200CPSI, 100CPSI and 0.00 CPSI equate to sqeezing 400 small squares into a 1.0″ sqaure all the way down to only 100 square cells per 1.00″ square. As one goes dwon the scale from 400 cells per inch to 100 CPSI you will be less backpressure and restriction per unit area given the same design criteria an washcoat.
Stock catalytic converters typically feature 600-800 CPSI, which provides excellent emissions control but restricts flow. High-flow cats usually range from 100 to 400 CPSI. Lower cell counts mean larger openings and better flow, but they may not scrub emissions as effectively.
G-Sport designed our high-flow Advanced Catalytic Converters with 300 and 400 cells per square inch (CPSI). Our advanced substrate design, combined with our proprietary wash coat nano-technology, ensures the highest level of emissions reduction with comparable flow rates of similar 200 CPSI converters on the market. This demonstrates that modern high-flow cats can achieve strong emissions performance while still improving flow.
Quality matters significantly. Cheap 200-cell cats often fail to provide adequate emissions control and may trigger check engine lights. Premium high-flow cats use metallic substrates instead of ceramic, which offer better durability, heat resistance, and flow characteristics.
Understanding Exhaust System Components
Your exhaust system consists of several interconnected parts that work together to manage exhaust flow and emissions:
- Headers/Exhaust Manifolds: Collect exhaust gases from the engine cylinders
- Midpipes/Test Pipes: Connect headers to catalytic converters or the rest of the exhaust
- Catalytic Converters: Reduce harmful emissions through chemical reactions
- Resonators: Fine-tune exhaust sound
- Mufflers: Reduce overall exhaust noise
Stock exhaust manifolds and catalytic converters are designed primarily for cost-effectiveness, durability, and emissions compliance. The OEM manifolds cannot boost the exhaust flow rate the same way headers can, and manifolds have a small design to take up as little space as possible. This conservative design leaves room for performance improvements through aftermarket upgrades.
Performance Impact: Power Gains Explained
Horsepower and Torque Gains from Headers
Headers deliver measurable power improvements by reducing exhaust backpressure and improving scavenging. The horsepower gains from exhaust headers can vary between different engines, typically ranging from an additional 5 to 20 horsepower depending on the specific setup.
Aftermarket headers can yield anywhere from 5 to 20+ additional horsepower, with larger gains seen in heavily modified, high performance engines that are moving a lot of air and a lot of exhaust gas out of the chamber. The actual gains depend on your engine’s displacement, compression ratio, camshaft profile, and overall tune.
Real-world testing confirms these numbers. Peak-horsepower improvements were actually even more impressive with a 70hp gain at 6,200 rpm. We did the math and came up with a staggering average increase of 46 lb-ft of torque. However, this test involved a modified engine, so stock applications will see more modest gains.
Long-tube headers typically outperform shorty headers. The long-tube headers outperformed the shorties. At the peak, horsepower jumped from 313 to 324 (an 11hp increase) and torque climbed from 329 to 346 (17 lb-ft), however, at 3,600 rpm, torque was up about 30 lb-ft.
Power Gains from High-Flow Catalytic Converters
High-flow catalytic converters provide more modest power improvements compared to headers. By reducing backpressure, high flow catalytic converters can help in improving engine efficiency and potentially increasing horsepower. However, the exact gains can vary based on the vehicle model and other modifications.
High-flow cats allow for the more efficient flow of exhaust gasses, removing restrictions that can impede performance. Vehicle owners who’ve significantly upgraded their engine power output will notice more power by upgrading. Same goes for any vehicle with old or cheap catalytic converters that are impeding flow. However, if you have a stock engine with no modifications, and relatively new OEM catalytic converters, you won’t see much of performance increase going with high flow cats.
For modified vehicles, the benefits are more pronounced. If you have a modified car with significantly more engine power than stock (20% increase or better), you will almost certainly see improved engine power switching to high flow catalytic converters (especially top-end performance as measured on a dyno).
Expect gains of 5-15 horsepower on modified vehicles, with the higher end of that range applying to heavily modified or forced-induction applications. On stock vehicles, gains may be negligible or nonexistent.
Understanding Backpressure: Myth vs. Reality
There’s a persistent myth that engines need some backpressure to perform well. This is fundamentally incorrect. It is a widely spread myth that some back pressure on the exhaust is good, however this is the wrong conclusion of experimentation. Back pressure on the VQ’s exhaust does not increase performance for naturally aspirated (NA) or turbo applications.
When backpressure builds up, the engine has to use more horsepower just to push those exhaust gasses out. This is called pumping loss — horsepower wasted on overcoming resistance instead of driving the vehicle. Less power, poor fuel economy, and a less efficient engine.
The confusion arises from misunderstanding exhaust velocity. When someone installs an oversized exhaust pipe, they may lose power—not because they eliminated backpressure, but because they killed exhaust velocity. Properly sized exhaust components minimize backpressure while maintaining optimal gas velocity for effective scavenging.
Sound Characteristics: What to Expect
Headers and Exhaust Note
Headers significantly change your vehicle’s exhaust sound. They increase volume and alter the tone, typically producing a sharper, more aggressive note with increased rasp or growl. The sound becomes more raw and mechanical, which enthusiasts often describe as a “race car” sound.
Long-tube headers are particularly loud, especially when combined with catless configurations. Although many enthusiasts love the sound of an exhaust outfitted with long tube headers, it’s rarely a popular choice with the neighbors. These headers have a tendency to be incredibly loud.
The increased volume can become droning on long highway drives, which is an important consideration for daily drivers. Shorty headers produce a more moderate sound increase compared to long-tubes.
High-Flow Cats and Sound
High-flow catalytic converters have a minimal impact on exhaust sound compared to headers. They smooth out exhaust flow slightly and may add a subtle depth to the tone, but the change is far less dramatic than with headers or catless setups.
One significant advantage: high-flow cats eliminate the raw gasoline smell that comes with running catless or using test pipes. This makes them much more pleasant for daily driving and reduces the likelihood of complaints from passengers or neighbors.
If you want to maintain a relatively quiet, stock-like sound while improving flow, high-flow cats are the better choice. If you want a loud, aggressive exhaust note, headers—especially long-tubes—will deliver that experience.
Emissions and Legal Compliance
How Modifications Affect Emissions
Any exhaust modification can impact your vehicle’s emissions output. Headers that remove or relocate catalytic converters will significantly increase harmful emissions. A catalytic converter’s primary job is to convert harmful gases produced during combustion – like hydrocarbons, carbon monoxide, and nitrogen oxides – into less harmful substances before they exit through the exhaust.
Catless headers or test pipes will almost certainly cause you to fail emissions testing. High-flow catalytic converters are designed to maintain emissions control while improving flow. A high-flow catalytic converter is designed to perform the same emissions-cleaning role as a standard catalytic converter but with far fewer restrictions to exhaust flow. By using advanced materials and construction techniques, high-flow cats allow exhaust gases to pass through more freely.
The effectiveness of high-flow cats depends on their cell count and quality. The EPA & Federal Government would say 400 cells is best as it scrubs exhaust the very best and allows the least pollutants and makes the car the most quiet. For car enthusiats like all of US………going to 200 or 100 cells or to NO CAT if that is allowed or permitted is the way to go.
Smog Tests and Inspections
Smog checks verify that your vehicle’s emissions fall within legal limits. Most jurisdictions require functioning catalytic converters to pass. High-flow cats can help you pass by maintaining emissions control while improving flow. Running headers without cats virtually guarantees failure.
Inspectors may perform visual checks or use sensors to detect missing or modified emissions equipment. Rules vary significantly by state and country. Some states have strict visual inspection requirements, while others rely primarily on tailpipe emissions measurements.
The EPA and California Air Resources Board (CARB) have strict standards. Many aftermarket high-flow catalytic converters are not legal for road use unless they are CARB-compliant and carry an Executive Order (EO) number. Non-compliant units are for off-road or track use only.
Always verify local regulations before purchasing or installing exhaust modifications. What’s legal in one state may result in fines or failed inspections in another.
Check Engine Lights and Sensor Issues
Modern vehicles use oxygen sensors (O2 sensors) to monitor exhaust gases and catalytic converter efficiency. The Engine Control Module (ECM) compares readings from upstream and downstream O2 sensors to verify the catalytic converter is working properly.
Removing or significantly altering catalytic converters often triggers a check engine light. Seeing that many cars aren’t programmed with high flow catalytic converters in mind, they may not be happy with you adding it. The onboard computer, in particular, may not have been calibrated properly, thus throwing out false-positive error codes. The most common diagnostic trouble codes that you may encounter are the P0430 and P0420 codes.
High-flow catalytic converters are generally designed to work with factory O2 sensors and avoid triggering check engine lights, but success depends on the quality of the converter and your vehicle’s year. GEN2 (400 CPSI) converters are designed to prevent catalyst efficiency-related CELs, especially in 2017 and newer vehicles, which utilize more advanced OBD monitoring. GEN1 (300 CPSI) converters typically function without triggering a CEL in vehicles 2016 and older.
Installing O2 sensors in the wrong location or removing them entirely will almost certainly trigger a check engine light and cause you to fail emissions testing. Proper installation and sensor placement are critical for avoiding these issues.
Headers vs. High-Flow Cats: Direct Comparison
Performance Perspective
Headers are the clear winner for maximum power gains. They provide the most significant horsepower and torque improvements, especially at higher RPMs. Long-tube headers deliver the best performance but require more extensive installation and may necessitate custom tuning.
High-flow catalytic converters offer modest performance improvements with minimal downsides. They’re most beneficial on modified vehicles where the stock cats have become a bottleneck. On stock vehicles, the gains are often negligible.
Sound and Driving Experience
Headers dramatically change your vehicle’s sound, making it louder and more aggressive. This appeals to enthusiasts but can be fatiguing on long drives and may draw unwanted attention.
High-flow cats maintain a relatively stock-like sound while eliminating the unpleasant smell of catless setups. They’re ideal for drivers who want improved flow without the noise and attention that comes with headers.
Emissions and Legality
High-flow catalytic converters are designed to maintain emissions compliance and help you pass inspections. Quality units with appropriate cell counts (300-400 CPSI) can meet EPA standards while still improving flow.
Headers, particularly catless or long-tube designs, often create emissions compliance issues. They may be illegal for street use in many jurisdictions and will likely cause you to fail emissions testing.
Installation and Cost
Shorty headers are relatively straightforward to install and typically work with existing exhaust systems. Long-tube headers require more extensive installation, often necessitating modifications to the exhaust system and potentially requiring custom tuning.
Most long tube headers will require that you receive a custom tune. This is due to the added airflow and replacement of the factory catalytic converters; whether you go catless or high-flow. Adding a custom tune will allow the PCM (Power Control Module) to balance the correct air-fuel management in the engine.
High-flow catalytic converters are generally easier to install, as they’re designed to replace stock cats in the same location. Quality high-flow cats range from $200-$800 each, while headers can cost anywhere from $300 to over $2,000 depending on design and materials.
Choosing the Right Upgrade for Your Vehicle
Daily Drivers and Street Cars
For daily drivers, high-flow catalytic converters offer the best balance of performance, legality, and livability. They improve flow without creating excessive noise or emissions compliance issues. Pair them with a quality cat-back exhaust for a noticeable improvement in sound and performance.
If you want headers on a daily driver, shorty headers are the better choice. They provide power gains without the extreme volume and installation complexity of long-tubes. Ensure they’re catted to maintain emissions compliance.
Track and Performance Vehicles
For track-focused vehicles, long-tube headers deliver maximum performance gains. Long tube headers are best for track cars or other machines that spend most of their time in the higher end of the RPM range. Combine them with high-flow cats (or catless if legal for off-road use) for optimal flow.
Keep in mind that you’ll likely need custom tuning to maximize the benefits and prevent check engine lights. Budget for professional installation and dyno tuning as part of your upgrade.
Modified and Forced Induction Vehicles
Heavily modified vehicles benefit most from comprehensive exhaust upgrades. If you’ve added a supercharger, turbocharger, or significant engine modifications, both headers and high-flow cats can provide substantial benefits.
The stock exhaust system becomes a major bottleneck on modified engines. If you’ve added a supercharger or turbocharger to your vehicle – or substantially increased the boost of an existing supercharger or turbo – you’ll likely find high flow cats a good investment.
Budget Considerations
If budget is a primary concern, start with high-flow catalytic converters. They provide meaningful improvements at a lower cost and with less installation complexity than headers. You can always add headers later as your budget allows.
Avoid cheap, low-quality parts. Inexpensive 200-cell cats often fail to control emissions properly and may trigger check engine lights. Similarly, poorly designed headers can actually hurt performance and create fitment issues.
Combining Headers and High-Flow Cats
For maximum performance, many enthusiasts install both headers and high-flow catalytic converters. This combination provides the best flow from the engine all the way through the exhaust system.
When combining these upgrades, consider catted long-tube headers with high-flow cats integrated, or install separate high-flow cats downstream of the headers. This maintains some emissions control while maximizing flow.
The combined approach requires careful planning. Ensure all components are properly sized and compatible. Professional installation and custom tuning are highly recommended to achieve optimal results and avoid check engine lights.
Key Takeaways
Headers and high-flow catalytic converters serve different purposes in your exhaust system. Headers maximize power output and create an aggressive sound but may create emissions compliance issues. High-flow cats improve flow while maintaining emissions control, making them more suitable for street-legal vehicles.
Your choice depends on your priorities:
- Maximum power: Long-tube headers deliver the biggest gains
- Emissions compliance: High-flow cats keep you street-legal
- Daily driving: Shorty headers or high-flow cats offer the best balance
- Track use: Long-tube headers with high-flow or catless pipes provide optimal performance
Consider your local emissions regulations, intended use, and budget when making your decision. Quality components from reputable manufacturers will provide better performance, durability, and emissions compliance than cheap alternatives.
For more information on exhaust system design and performance, consult resources from the Society of Automotive Engineers or EPA vehicle emissions standards. Professional tuners and exhaust specialists can also provide valuable guidance specific to your vehicle and goals.