Top 10 Best Air Filter For WRX That Boost Performance Fast

Like many Subaru WRX drivers, you want to keep your engine running smoothly while protecting it from harmful dust and debris. Choosing the best air filter for WRX can make a noticeable difference in performance and engine longevity.

This product is ideal for daily drivers and those who want reliable engine protection without complicated installations. In this review, we will explore several leading air filters for the WRX.

You’ll learn about their build quality, filtration ability, ease of maintenance, and how each option might fit your needs. By the end, you’ll have a clearer idea of which air filter suits your WRX best.

Top Choices to Boost Your Subaru’s Performance and Airflow

Image	Product	Price
Our Recommended 1	K&N Engine Air Filter: Long Life 18,000 Mile Replacement Air	Check Price
Our Recommended 2	Engine+Cabin Air Filters Fit for Crosstrek 16-17, Forester 09-18, Impreza	Check Price
Our Recommended 3	EPAuto CP930 (CF10930) Cabin Air Filter Replacement for Subaru Forester	Check Price

1. K&N Engine Air Filter: Long Life 18,000 Mile Replacement Air

Improve your Subaru WRX’s engine efficiency with the K&N Engine Air Filter. Designed for durability and high performance, this air filter ensures long-lasting protection and optimum airflow.

Its rugged build offers reliable operation through 18,000 miles of use, making it a solid upgrade for your vehicle’s intake system.

Offering a balance between excellent filtration and extended lifespan, the K&N Advantage Plus Air Filter stands out among replacement options. It uses premium media to provide superior engine protection with up to 99% filtration efficiency.

The K&N Advantage Plus Air Filter is crafted from durable materials to withstand harsh driving conditions. It lasts 50% longer than standard filters rated for 12,000 miles, making it cost-effective for steady use.

The filter’s design maintains steady airflow, supporting improved engine responsiveness and fuel efficiency without compromising cleanliness.

Installation is straightforward, fitting easily into the WRX’s air intake system without modifications. This makes the filter suitable for daily drivers and those who cover significant mileage. Additionally, the product includes a 1-year limited warranty, guaranteeing peace of mind for consumers seeking reliable aftermarket parts.

Additionally, the product includes a 1-year limited warranty, guaranteeing peace of mind for consumers seeking reliable aftermarket parts.

Compared to many typical replacement air filters, the K&N model delivers an excellent combination of long life, robust construction, and high filtration standards. It is an ideal choice for Subaru WRX owners focused on engine performance and longevity without constant replacements or expensive maintenance.

Pros

• Extended lifespan of up to 18,000 miles between replacements
• Premium filter media providing 99% filtration efficiency
• Durable build designed for rugged conditions

Cons

• May require occasional cleaning for optimal performance beyond mileage

The K&N Engine Air Filter offers a dependable and long-lasting solution for WRX owners seeking to maintain engine health. Its balance of filtration effectiveness and rugged durability makes it a valuable upgrade for sustained driving conditions.

2. Engine+Cabin Air Filters Fit for Crosstrek 16-17, Forester 09-18, Impreza

Enhance your vehicle’s performance and interior air quality with the Engine+Cabin Air Filters designed for select Subaru models. These filters provide reliable protection by keeping the engine and cabin air clean, supporting smoother operation and a healthier driving environment.

Crafted to meet the specifications of several Subaru vehicles including WRX and Forester, these air filters deliver high filtration precision. They help maintain engine efficiency while reducing noise, ensuring a comfortable ride every time.

Engine+Cabin Air Filters by RVgolf are designed to fit various Subaru models such as Crosstrek (2016-2017) and WRX (2013-2021). The engine filter uses a high-fiber structure that removes 99% of airborne impurities, helping protect engine components and performance.

The filters feature a low resistance design for improved air intake, which decreases engine noise and vibrations. Additionally, the cabin filter minimizes airflow noise, promoting quieter operation of the AC system. Installation is straightforward and can be done quickly without professional help, making maintenance hassle-free.

These filters are perfect for Subaru owners who value engine longevity and in-cabin air quality. Their durable build and efficient filtration system ensure lasting protection, enhancing overall vehicle comfort and performance.

Routine replacement every 12 months or 12,000 miles is recommended for optimal results.

Pros

• High filtration efficiency removing 99% of impurities from engine air
• Multi-layer cabin filter material improves interior air quality
• Easy installation suitable for multiple Subaru models

Cons

• Compatibility limited to specific Subaru model years; verify before purchase

The RVgolf Engine+Cabin Air Filters offer a balance of efficiency, ease of use, and durability. They suit Subaru drivers aiming to maintain engine health and enjoy cleaner cabin air. Compared to generic filters, these provide tailored fitment and consistent performance for select WRX and Crosstrek models.

3. EPAuto CP930 (CF10930) Cabin Air Filter Replacement for Subaru Forester

Maintaining clean air inside your vehicle dramatically improves driving comfort and health. The EPAuto CP930 Cabin Air Filter Replacement is designed specifically to refresh the air quality for Subaru drivers, offering a clean and fresh cabin environment.

By removing contaminants and odors, it enhances the overall driving experience. This cabin air filter supports your vehicle’s HVAC system for smooth airflow and consistent ventilation.

Offering a perfect match to Subaru models including Forester, WRX, and Crosstrek, this filter uses soda and activated carbon to neutralize unpleasant odors and refresh cabin air. Its enhanced filtration efficiently traps dust, pollen, and pollutants.

Constructed as a reliable replacement part, it maintains the original air quality standards for your vehicle. Installation is straightforward, making annual replacement convenient and hassle-free.

Compatible with popular models from 2008 through 2021, it blends durability with effective performance. Regular use supports HVAC efficiency, prolonging system life and keeping the interior environment healthier.

The EPAuto CP930 fits within the same specifications as Subaru Genuine Part# 72880-FG000 and the FRAM CF10930, ensuring trustworthy quality. It’s well-suited for anyone seeking an easy-to-install, efficient air filtration upgrade for their Subaru vehicle fleet.

Pros

• Effective odor elimination using soda and carbon layers
• Compatible with a wide range of Subaru models including WRX and Forester
• Enhances HVAC system performance and airflow

Cons

• Requires replacement every 12 months or 12,000 miles for best results

The EPAuto CP930 Cabin Air Filter replacement provides a practical solution to breathe fresher air on every drive. It balances quality, performance, and compatibility at an accessible level for Subaru owners aiming to maintain a clean cabin environment effortlessly.

4. K&N High-Flow Original Lifetime Engine Air Filter: Increase Power: Premium,

Upgrade your Subaru WRX with a high-performance engine air filter designed to boost power and improve acceleration. The K&N High-Flow Original Lifetime Engine Air Filter offers reliable airflow and consistent engine protection for enhanced driving experiences. Experience increased horsepower alongside long-lasting durability with a product engineered for premium performance.

Experience increased horsepower alongside long-lasting durability with a product engineered for premium performance.

Made with premium materials, this air filter employs multiple layers of cotton gauze combined with a special tacking treatment. This design traps harmful contaminants effectively while maintaining optimal airflow to your engine.

The filter fits seamlessly into your vehicle’s factory air box, making installation quick and straightforward. It requires cleaning only once every 75,000 miles under typical driving conditions, ensuring minimal maintenance efforts. Manufactured using advanced construction methods, the filter promises lasting use and comes with a limited lifetime warranty for peace of mind.

Compatible with a variety of Subaru models including the WRX, Forester, and Impreza from 2003 to 2019, it offers broad application versatility. Its rugged build supports the demands of everyday driving and spirited performance, helping maximize engine response and fuel efficiency.

Pros

• Enhances horsepower and acceleration by improving airflow
• Durable construction with four layers of contaminant-blocking cotton gauze
• Washable and reusable, reducing environmental impact and long-term costs

Cons

• Requires periodic cleaning to maintain peak performance

Combining longevity, performance, and ease of use, the K&N High-Flow Engine Air Filter stands out as a practical upgrade for Subaru WRX owners. Compared to standard disposable filters, its reusable design is a cost-effective investment that supports sustained vehicle performance over time. This filter meets a balance of quality and function that appeals to drivers seeking dependable engine care.

This filter meets a balance of quality and function that appeals to drivers seeking dependable engine care.

5. EPAuto GP997 (CA9997) Panel Engine Air Filter, Compatible with Subaru

The EPAuto GP997 (CA9997) Panel Engine Air Filter offers reliable and precise compatibility with various Subaru models. Designed to deliver clean airflow, it enhances engine efficiency and protects internal components from harmful dirt and debris.

This air filter supports stable vehicle performance over time. Its trusted fit and filtration quality help maintain engine health through consistent air quality control.

Precision-crafted to fit models like Subaru WRX (2012-2021) and Impreza (2008-2016), the EPAuto GP997 ensures seamless installation without modifications. It replaces original parts such as 16546-AA090 and matches FRAM CA9997 standards for dependable operation.

The filter’s design aids in keeping dirt from entering the engine, which can extend overall vehicle life and sustain performance.

Manufactured by EPAuto, it weighs just 8 ounces, combining lightweight construction with durable materials. The filter promotes enhanced fuel mileage by maintaining clean air intake and reducing engine strain. Recommended replacement every 12,000 miles supports continued engine efficiency.

Recommended replacement every 12,000 miles supports continued engine efficiency.

Its ease of use and direct-fit compatibility make it ideal for vehicle owners looking for a hassle-free maintenance update. The EPAuto GP997 suits daily drivers and long-distance commuters who demand consistent engine protection and smoother performance from their Subaru vehicles.

Pros

• Precise fit for multiple Subaru models, including WRX and STI lines
• High-quality filtration that prevents dirt infiltration and protects the engine
• Helps improve fuel efficiency and extend engine performance over time

Cons

• Replacement interval requires attention to maintain optimal performance

Offering a dependable alternative to original Subaru filters, the EPAuto GP997 balances cost-effectiveness with quality. It supports essential engine maintenance and suits drivers seeking hassle-free compatibility and reliable air filtration for their WRX and other Subaru models.

6. K&N High-Flow Original Lifetime Engine Air Filter: Increase Power: Premium,

Enhance your WRX’s engine performance with the K&N High-Flow Original Lifetime Engine Air Filter. Designed to boost horsepower and acceleration, this premium air filter combines advanced technology with durable materials for enduring results.

Engineered for both power and longevity, it offers a smart upgrade for those seeking reliable and consistent airflow. Its rugged construction ensures it stands the test of time without compromising on efficiency.

The K&N High-Flow Air Filter uses state-of-the-art cotton gauze media treated to trap contaminants while allowing maximum airflow. Multiple layers work together to protect your engine from harmful particles, improving combustion efficiency. This design helps increase acceleration and overall horsepower, ensuring better vehicle response.

Durability is a core strength, as the filter is built with premium materials and cutting-edge techniques to last a lifetime. Unlike disposable filters, it requires cleaning only every 75,000 miles under normal conditions.

Environmentally conscious drivers will value its washable and reusable nature, reducing waste compared to numerous disposable replacements. Built in the USA, the filter also carries a limited lifetime warranty, adding peace of mind for long-term ownership.

Ideal for WRX owners who want a hassle-free upgrade offering measurable gains in power and engine protection.

Pros

• Increases horsepower and acceleration through superior airflow
• Durable, washable, and reusable design minimizes replacement costs
• Easy installation with pre-oiled, factory-fit design

Cons

• Cleaning required every 75,000 miles, which might be longer than some prefer

The K&N High-Flow Original Air Filter stands out as a smart investment for WRX drivers seeking improved engine performance and longevity. Its robust design and ease of maintenance make it a preferred choice over standard disposable filters.

7. Subaru Engine Element Air Filter for Outback Legacy Impreza WRX

Keep your Subaru running smoothly with the Engine Element Air Filter designed specifically for WRX and other Subaru models. This genuine OEM filter safeguards your engine from dirt and debris while maintaining optimal airflow for performance.

Engineered to meet Subaru’s exact specifications, this air filter supports clean and efficient engine operation. It suits a wide range of Subaru vehicles, including Outback, Legacy, Impreza, WRX, Forester, XV Crosstrek, and Tribeca models.

Its durable construction ensures lasting protection against contaminants without compromising airflow, which helps maintain fuel efficiency and power output.

Designed for straightforward installation, the filter fits precisely in the air cleaner housing, making replacement hassle-free. The genuine Subaru part number 16546AA10A aligns perfectly to retain your vehicle’s warranty and performance. It holds up well under various driving conditions, from city commutes to highway cruising.

The air filter’s lightweight design at just half a pound adds minimal weight to your vehicle, ensuring no effect on handling. Its build quality sustains cleanliness longer than many aftermarket alternatives.

Pros

• Perfect OEM fit for multiple Subaru models including WRX and Outback
• Durable construction ensures long-lasting engine protection
• Easy installation supports quick replacement and maintenance

Cons

• Limited to Subaru-specific vehicle compatibility

Offering precise design for Subaru engines, this air filter delivers reliable filtration with minimal effort. Its genuine OEM status guarantees confidence in performance and longevity, making it a dependable choice for maintaining your WRX and related Subaru vehicles.

Opting for this filter helps preserve engine health and efficiency with ease.

8. Cabin and Engine Air Filter Set for Forester (2019 2020

Maintaining clean air inside your vehicle and protecting the engine are vital for a smooth and healthy driving experience. The Cabin and Engine Air Filter Set for Forester (2019-2024) and WRX (2022-2024) offers reliable filtration designed to keep dust, pollen, and harmful particles at bay.

Its precision fit and high filtration efficiency serve both passenger comfort and engine longevity effectively.

This filter set combines convenience with performance, providing two essential filters in one package. It fits specific Forester and WRX models, making it a tailored upgrade for compatible vehicles. The straightforward installation means you can replace your old filters quickly, restoring optimal airflow and cabin air quality with ease.

Designed to meet or exceed OEM specifications, the SERVKITOUR filter set guarantees dependable filtration for both the engine and cabin air. Each filter material captures airborne contaminants and prevents them from entering the engine or passenger compartment.

The engine air filter supports better fuel efficiency by maintaining clean airflow, while the cabin air filter enhances in-cabin air quality for a more comfortable ride.

Durable construction and precise engineering deliver long-lasting performance, reducing the frequency of replacements. This set suits drivers seeking dependable protection without compromise, especially those owning compatible Forester or WRX models.

The package includes both filters, offering double protection with one purchase, delivering excellent value and peace of mind.

Additionally, this filter set features compatibility with a range of reference numbers, ensuring it fits multiple versions. Regular replacement is recommended every 12 months or 12,000 miles to maintain optimal function.

Its balance of quality, fit, and performance makes it a practical choice for automotive care.

Pros

• High-performance filtration for engine and cabin air
• Fits Forester (2019-2024) and WRX (2022-2024) models precisely
• Durable design ensures long-lasting use and reliability

Cons

• Limited to specific vehicle models, check compatibility before purchase

This filter set offers an effective and hassle-free solution for maintaining clean air in your vehicle and protecting the engine. It delivers strong performance and fits select Forester and WRX models perfectly, making it a dependable option for quality-conscious drivers.

9. CA9997 Engine Air Filter for Subaru 2008-2016 Impreza,2009-2018 Forester,2005-2019 Legacy,2005-2019

Upgrade your Subaru’s performance with the CA9997 Engine Air Filter, crafted to protect and enhance engine efficiency. Designed specifically for a wide range of Subaru models from 2005 to 2021, this replacement air filter ensures your vehicle breathes cleaner air while maintaining smooth operation.

Reliable filtration is vital to prevent engine wear caused by dust and particles. The CA9997 air filter offers a cost-effective yet quality solution, tailored to keep your vehicle running longer and cleaner.

Whether you drive a WRX, Forester, or Legacy, this filter fits perfectly and performs consistently.

The CA9997 Engine Air Filter matches OE part numbers A35592, CF10285, CP285, and several others, ensuring compatibility and easy replacement for Subaru models like the 13-21 WRX and 15-18 WRX STI. It traps harmful debris efficiently, protecting the engine during daily drives, which reduces wear and potential costly repairs.

Constructed from premium composite fiber filter paper, it features a small aperture that balances breathability with precise filtering. This material extends the filter’s dust holding capacity, helping maintain optimal engine airflow.

This aftermarket alternative delivers excellent value without compromising reliability. Its design suits drivers who demand dependable engine protection, particularly those owning Subaru’s popular performance and crossover vehicles.

Regular replacement with this filter supports better engine health and enhanced fuel efficiency.

Pros

• Fits a wide range of Subaru models from 2005 to 2021, including WRX and Legacy variants
• High-quality composite fiber filter paper provides strong filtration and breathability
• Easy to install as a direct replacement for OEM filters without extra tools

Cons

• Does not include an instruction manual, which may require some user experience for installation

The CA9997 Engine Air Filter presents a smart upgrade for Subaru owners wanting reliable engine protection and improved air filtration. Its solid build and vehicle fitment make it a practical choice compared to other aftermarket filters, offering peace of mind and extended engine life with minimal effort.

10. K&N Engine Air Filter: Long Life 18,000 Mile Replacement Air

The K&N Engine Air Filter offers a highly durable option designed for long-lasting performance. Crafted to provide up to 18,000 miles of use, it keeps your engine protected and running efficiently. Its robust build combined with superior filtration sets it apart from standard filters.

Its robust build combined with superior filtration sets it apart from standard filters.

Designed for drivers seeking reliable air filtration, the K&N Advantage Plus Air Filter delivers excellent service life and engine protection without the frequent replacements. Engineered with premium media, it maximizes airflow while maintaining up to 99% filtration efficiency for cleaner engine operation.

Constructed from high-quality materials, the K&N Advantage Plus Air Filter outperforms typical filters by providing an extended service life of 18,000 miles. This longevity reduces maintenance frequency, making it ideal for drivers predominantly on highways. The filter media efficiently captures harmful particles, helping safeguard engine components from wear and tear.

Installation is straightforward, fitting easily in compatible vehicles without requiring modifications. The design maintains optimal airflow to the engine, which supports better performance and fuel efficiency.

Suitable for drivers prioritizing long-term reliability, this air filter is especially advantageous for those commuting regularly or taking extended road trips. Compared to standard 12,000-mile filters, it offers up to 50% longer filter life while maintaining strong filtration criteria.

Its balance of quality, ease of use, and engine protection represents solid value for a replacement air filter.

Pros

• Durable construction supports up to 18,000 miles of use
• Maintains 99% filtration efficiency to protect the engine
• Simple installation compatible with multiple vehicle models

Cons

• Replacement needed every 18,000 miles, which may be long for some use cases

This K&N air filter stands out by offering extended durability and high filtration performance. It provides a well-rounded choice for drivers seeking dependable engine protection combined with ease of maintenance. Its longevity and quality make it a valuable upgrade over conventional filters.

Its longevity and quality make it a valuable upgrade over conventional filters.

Top 5 Best Air Filters for WRX in 2024: Buyer’s Guide

Ease of installation and maintenance

Choosing the best air filter for WRX involves paying attention to how easy it is to install and maintain. Filters with straightforward installation processes help save time and reduce frustration, especially for beginners.

Maintenance also plays a significant role; some filters need cleaning or replacement more often than others, so understanding how frequently this should be done can help keep the vehicle’s performance steady without extra hassle. Availability of necessary tools or accessories, such as cleaning kits or replacement parts, can influence the overall experience, making upkeep more convenient and manageable for someone new to car maintenance.

Compatibility with subaru wrx models

When selecting an air filter for a Subaru WRX, paying attention to model year fitment ensures the filter matches the specific design of your vehicle’s intake system. Different engine types within the WRX lineup, such as turbocharged variants, may require filters that handle airflow and filtration differently to maintain engine performance and efficiency.

Choosing between original equipment manufacturer (OEM) and aftermarket options depends on personal preferences and priorities; OEM filters typically offer guaranteed compatibility and reliable quality, while aftermarket filters can provide enhanced filtration technology or improved airflow, sometimes at a more competitive price point. Considering these aspects can help you find an air filter that supports your car’s performance while fitting seamlessly with its configuration and your driving needs.

Price and warranty

When selecting the best air filter for WRX, understanding the price range and value offered can guide you toward the most suitable choice. Some filters come at a higher upfront cost but deliver greater durability and efficiency, potentially saving money in the long run through improved engine performance and longevity.

Warranty terms often reflect the manufacturer’s confidence in the product’s quality, with longer coverage periods providing added peace of mind. Additionally, reliable customer support can make a difference if any issues arise or if guidance is needed during installation or product questions.

Balancing these factors can help ensure that your investment in an air filter provides consistent and lasting benefits tailored to your WRX’s needs.

Filter material and build quality

The best air filter for WRX vehicles varies depending on the filter material and build quality, which play a significant role in performance and longevity. Common types of filter media include cotton, foam, and synthetic materials, each offering distinct advantages.

Cotton filters tend to provide excellent airflow and are often washable, making them reusable after proper cleaning. Foam filters usually deliver good filtration and can also be washable, but may require more frequent maintenance. Synthetic filters often balance filtration efficiency with durability and can be disposable or washable depending on the specific product.

Durability and lifespan largely depend on the material and how well the filter is constructed. Washable filters are a popular choice for cost-effectiveness over time, as they can be cleaned and reused multiple times, but they require proper care to maintain effectiveness.

When selecting a filter, considering how often it will need replacement or cleaning alongside the driving conditions and performance expectations can help in making a choice that best suits the WRX’s requirements.

Performance impact

When selecting an air filter aimed at improving a WRX’s performance, it is helpful to focus on how the device balances airflow and filtration efficiency. Filters that allow higher airflow can help the engine breathe more easily, potentially enhancing horsepower and throttle response by reducing air resistance. However, maintaining effective filtration is equally important to protect the engine from harmful particles that can cause wear over time.

However, maintaining effective filtration is equally important to protect the engine from harmful particles that can cause wear over time. Improvements in airflow may contribute to a noticeable difference in throttle responsiveness, making acceleration feel smoother and more immediate. Additionally, a well-designed air filter can influence fuel economy by optimizing the air-to-fuel ratio, which may lead to more efficient combustion and slightly better mileage.

When choosing, consider filters made from quality materials that provide both durability and adequate filtration, ensuring a consistent performance boost without sacrificing engine protection. Understanding the balance between these factors aids in selecting a product that supports both longevity and subtle improvements in driving dynamics.

Customer reviews and brand reputation

When choosing the best air filter for WRX models, many WRX owners tend to favor trusted brands known for their durability and effective filtration performance. These brands often balance enhanced airflow with solid particle trapping, which helps maintain engine health and improve fuel efficiency. Users commonly praise features like easy installation, washable designs for reusable filters, and compatibility with performance tuning.

Some common issues encountered include filters that may require more frequent cleaning or those that do not fit perfectly without slight adjustments, but these are generally manageable. Considering how the filter will be used—whether for daily driving, spirited weekend runs, or track days—helps determine the right type, such as standard paper filters versus high-flow cotton or synthetic options.

Observing what fellow WRX owners frequently mention about their experiences can guide in avoiding common pitfalls and gaining benefits from features that enhance both engine protection and power delivery.

People Also Asked

What Factors Should I Consider When Choosing An Air Filter For My Wrx?

When choosing an air filter for your WRX, consider factors like filtration efficiency, airflow performance, and compatibility with your vehicle model. Additionally, decide between reusable or disposable filters based on maintenance preferences and driving conditions.

How Often Should You Replace The Air Filter In A Wrx?

You should replace the air filter in a WRX every 12,000 to 15,000 miles or approximately once a year. However, if you drive in dusty or harsh conditions, more frequent replacement may be necessary.

Are Reusable Air Filters Better Than Disposable Ones For A Wrx?

Reusable air filters for a WRX can provide better long-term airflow and improved engine performance compared to disposable filters, as they are designed to be cleaned and reused multiple times. However, they require regular maintenance to ensure optimal function, while disposable filters offer convenience with less upkeep.

What Is The Best Air Filter Brand For A Subaru Wrx?

The best air filter brand for a Subaru WRX is typically K&N, known for its high-performance and reusable filters that enhance airflow and engine efficiency. Another popular option is AEM, which also offers durable and efficient air filters designed for sports cars like the WRX.

Will Upgrading The Air Filter Improve The Performance Of A Wrx?

Upgrading the air filter in a WRX can improve airflow to the engine, potentially enhancing throttle response and slightly increasing horsepower. However, the overall performance gains are usually modest unless combined with other modifications.

Conclusion

Choosing the best air filter for WRX involves balancing factors like filtration efficiency, airflow, and durability. High-quality options improve engine performance and longevity by providing cleaner air, while some models may require more frequent maintenance or cost more upfront. This filter is particularly suitable for WRX owners prioritizing consistent performance and protection against contaminants.

Buyers concerned about installation or compatibility can often find user-friendly designs tailored specifically to WRX models, minimizing hassle. Ultimately, selecting the right air filter depends on your driving habits and maintenance preferences.

The best air filter for WRX offers a reliable way to maintain engine health without compromising power, making it a practical choice for those looking to keep their vehicle running smoothly over time.