STI Engine Upgrades: A Guide to Reliable Power

Upgrading your Subaru STI is about more than just bolting on parts and hoping for the best. Your engine is a complex, interconnected system, and changing one component affects all the others. A new intake needs a tune to work correctly, and a bigger turbo demands a stronger fuel system to keep up. Thinking of your car as a complete system is the key to making smart choices. This guide breaks down the entire process of STI engine upgrades, from foundational breathing mods to the crucial supporting parts that ensure reliability. We’ll cover how each piece fits into the puzzle, helping you build a balanced and cohesive performance machine.

Key Takeaways

• Define Your Goals to Build a Smarter Car: Before buying any parts, decide if you're building a track machine or a powerful daily driver. A clear objective guides every purchase, ensuring you invest in components that work together to create a reliable and purposeful build.
• Support Every Horsepower You Add: Making more power requires more from your entire engine system. Upgrading your fuel delivery, cooling, and oil systems—and getting a professional tune—is non-negotiable for protecting your engine and ensuring your new power is safe and consistent.
• Adapt Your Maintenance for a Modified Engine: A modified STI operates under greater stress, so the factory service schedule no longer applies. Adopt a more frequent maintenance routine, especially for oil changes and fluid checks, to ensure the long-term health and reliability of your investment.

First Steps: Planning Your STI Engine Upgrade

Before you buy a single part, the most important work happens on paper. Planning your build is the key to getting the power you want without sacrificing the reliability you need. A well-thought-out strategy saves you time, money, and headaches down the road. By defining your goals and understanding the fundamentals, you can build an STI that’s both thrilling to drive and dependable for years to come. Let's walk through the essential first steps to get your project started on the right foot.

Define Your Performance Goals

First things first: what do you want your STI to do? Are you building a weekend track warrior, a daily driver with more punch, or a capable overlanding rig? Your answer will shape every decision you make. Knowing your endgame will help you select the right Subaru STI upgrades from the very beginning. A car built for autocross will have different needs than one designed for long-distance road trips. Be honest about how you’ll use your car 90% of the time. This clarity ensures you invest in parts that truly serve your purpose, creating a build that’s perfectly tailored to your driving style.

Set Realistic Power Targets

Everyone wants more horsepower, but it’s important to set achievable goals. A stock STI is already a potent machine, and modest gains can make a huge difference in how it feels. For many owners, a target of 350-400 wheel horsepower (WHP) is a great starting point that offers a significant performance jump without requiring a complete engine overhaul. A complete turbo-back exhaust paired with professional engine tuning services can get you there. Chasing huge numbers like 500+ WHP is possible, but it requires a much larger budget and more extensive supporting modifications. Start with a clear number in mind and build your plan around it.

Balance Power with Reliability

More power often puts more stress on your engine, but a powerful STI can also be a reliable one. The key is a balanced approach. Instead of just adding power, focus on strengthening the systems that support it. Fortunately, the stock STI transmission is incredibly robust and can handle anywhere from 600 to 900 horsepower, so you can focus your budget on building a reliable engine. Investing in quality performance parts for your fuel, oil, and cooling systems is just as important as the turbo you choose. A well-balanced build will give you the confidence to enjoy that extra power without worrying about what might break next.

Debunk Common Modification Myths

Let's clear the air on a few things. The world of car modification is full of myths that can lead you down the wrong path. One common mistake is chasing the classic “Subaru rumble” with aftermarket unequal length (UEL) headers. While they sound great, they often offer no real performance gain over the stock manifold and can be less durable. Another pitfall is buying cheap parts or skipping a professional tune to save money. This almost always costs more in the long run. Doing your research and listening to experienced builders will help you avoid these common modification pitfalls and ensure your money is well spent.

Core Upgrades for More Power

Once you have a clear plan, you can start exploring the parts that will bring your vision to life. These core upgrades are the foundation of nearly every powerful STI build. They work together to improve your engine's airflow, allowing it to take in more air, create a bigger bang, and exhale more efficiently. Think of it as helping your engine breathe better so it can perform at its peak. Each component plays a critical role, and upgrading them in a balanced way is key to making significant, reliable power.

While it’s tempting to go for the biggest turbo right away, a strategic approach will yield better results. Starting with foundational breathing mods like an intake and exhaust prepares your engine for more substantial upgrades down the line. Remember, every part you add needs to work in harmony with the others, and a professional tune is what ties everything together. Let’s look at the essential components for building more horsepower and torque.

Choose the Right Intake and Air Filter

Your engine needs to breathe, and a stock intake can be restrictive. Upgrading to a high-flow intake system is one of the first and most effective mods for your STI. A quality cold air intake pulls cooler, denser air from outside the hot engine bay, which helps your engine make more power. Paired with a less restrictive air filter, this upgrade allows the engine to inhale more freely. This simple change can improve throttle response and produce a satisfying induction sound, setting the stage for more significant power gains from future modifications.

Select Your Turbocharger

The turbocharger is the heart of your STI's power production. While the stock turbo is capable, upgrading to a larger or more efficient unit is necessary for making serious horsepower. When selecting a turbo, consider your power goals and driving style. A larger turbo can produce more top-end power but may introduce more lag, while a smaller, quicker-spooling turbo might be better for daily driving and autocross. Matching the right turbo to your engine setup and supporting mods is crucial for achieving a balanced and responsive performance build.

Improve Your Intercooler

Forcing more air into the engine with a turbo generates a lot of heat. An intercooler’s job is to cool that compressed air before it enters the engine. Cooler, denser air contains more oxygen, allowing for a more powerful combustion cycle. The stock top-mount intercooler can become heat-soaked, especially during aggressive driving or on hot days. Upgrading to a larger top-mount or a front-mount intercooler provides more consistent and efficient cooling, protecting your engine and ensuring you have reliable power when you need it most.

Upgrade Your Exhaust System

What goes in must come out. A restrictive factory exhaust system creates backpressure, which chokes the engine and forces the turbo to work harder. A complete turbo-back exhaust, which replaces everything from the turbo to the tailpipe, is one of the most effective Subaru STI Upgrades for a significant power gain. By creating a smoother path for exhaust gases to escape, you reduce backpressure, allowing the turbo to spool faster and the engine to operate more efficiently. This not only adds power but also gives your STI that iconic Subaru rumble.

What Power Gains to Expect

It’s important to have realistic expectations for power gains. With basic bolt-ons like an intake, a turbo-back exhaust, and a professional tune, many owners see gains of 25 to 30 wheel horsepower and a similar increase in torque. The real magic happens when these parts work together. Each upgrade complements the others, and the cumulative effect can be substantial. However, these numbers are highly dependent on the quality of the parts, the health of your engine, and—most importantly—the quality of your tune. A proper engine tuning service is essential to safely maximize the potential of your new hardware.

Build for Reliability: Essential Supporting Mods

Adding power is exciting, but without the right supporting modifications, you’re building a house on a shaky foundation. Pushing your engine harder generates more heat, places greater demand on your fuel system, and puts immense stress on your drivetrain. Neglecting these areas is a fast track to engine damage and costly repairs. True performance isn't just about a high horsepower number; it's about creating a balanced, reliable machine that can handle the power you throw at it, lap after lap or mile after mile. These essential mods ensure your engine stays healthy, your power delivery is consistent, and your investment is protected for the long haul.

Strengthen Your Fuel System

As you introduce more air into your engine with upgrades like a new intake or turbo, you need more fuel to maintain a safe air-to-fuel ratio. The stock fuel pump and injectors are only designed to handle factory power levels. Once you add a downpipe and a cold air intake, your car's fuel injectors will likely need to be upgraded to keep up. A lean condition—too much air, not enough fuel—can cause detonation and catastrophic engine failure. Upgrading to a higher-flow fuel pump, larger injectors, and an adjustable fuel pressure regulator ensures your engine gets the fuel it needs to make power safely and consistently.

Manage Your Engine with a Proper Tune

Think of an engine tune as the brain of your operation. It controls everything from fuel delivery and ignition timing to boost pressure. Most modifications, except for a cat-back exhaust and an Air Oil Separator (AOS), will require a proper engine tune. Bolting on parts without adjusting the ECU mapping is a major risk. A professional engine tuning service recalibrates your car’s computer to work with your new hardware, optimizing performance and ensuring the engine operates within safe parameters. Skipping this step can lead to poor performance at best and severe engine damage at worst.

Keep It Cool: Upgrade Your Cooling System

More power means more heat. The factory cooling system is adequate for a stock STI, but it can quickly become overwhelmed when you start adding performance parts that make the engine work harder and hotter. An upgraded radiator, a high-performance thermostat, or an external oil cooler are all excellent investments to help manage engine temperatures. Keeping your engine cool is critical for preventing overheating, maintaining consistent power during demanding driving, and ensuring the long-term reliability of your build. These parts are essential for anyone who plans on track days or spirited driving.

Protect Your Engine with Oil System Upgrades

Under high-performance conditions, oil can get into your intake system, contaminating the air-fuel mixture and effectively lowering your fuel's octane rating. This can lead to detonation, which is a major cause of engine failure in turbocharged Subarus. An Air Oil Separator (AOS) is one of the most important performance parts you can install, even if you're not running higher boost. It captures oil vapor from the crankcase ventilation system and returns it to the oil pan, ensuring only clean air enters your intake. This simple mod protects your engine and helps it run more efficiently.

Reinforce Your Drivetrain and Transmission

Your engine’s power is useless if the drivetrain can’t transfer it to the wheels. The stock STI transmission is robust, but it has its limits. The six-speed gear set is famously strong, capable of handling significant power increases and a high degree of driver abuse. As you add horsepower and torque, you should also consider upgrading your clutch to prevent slipping. For high-power builds, reinforcing other components like axles and driveshafts becomes necessary to create a bulletproof drivetrain that can handle the demands of performance driving.

How to Select Quality Parts

Once you have a plan, the next step is sourcing your components. The aftermarket is flooded with options, and it can be tough to tell the difference between a quality part and a cheap imitation. The parts you choose are the foundation of your build, and cutting corners here can lead to disappointment and costly repairs down the road. Investing in well-engineered components from the start ensures your STI not only makes power but also remains dependable, whether you're on a track day or a daily commute. This isn't just about bolting on shiny new hardware; it's about creating a cohesive system where every component works in harmony to achieve your performance goals safely.

Making smart choices comes down to four key principles: sticking with reputable brands, inspecting for quality construction, confirming compatibility, and finding the best overall value for your investment. Following these guidelines will help you build a parts list you can be confident in, setting you up for a successful and reliable engine upgrade. It’s about building an engine that you can trust to perform when you push it, without worrying if a subpar component is about to fail. Let's break down how to evaluate each part you consider for your build.

Find Reputable Brands

When you’re shopping for parts, brand reputation is your first line of defense against poor quality. Companies that have been in the Subaru performance scene for years have built their names on engineering, testing, and customer satisfaction. They stand behind their products because their success depends on it. While a no-name part on eBay might be tempting for its low price, you’re taking a gamble on its design, materials, and durability. Sticking with established brands means you’re buying a component that has been proven to work, often through countless hours of R&D and real-world testing by enthusiasts just like you. This is an investment in peace of mind and the long-term health of your engine.

Check for Quality Materials and Construction

Beyond the brand name, the physical quality of a part tells you a lot about its performance potential. High-quality components are made from superior materials designed to handle the increased stress of a modified engine. Look for signs of quality craftsmanship, like clean welds on an exhaust manifold, precision machining on a turbo compressor wheel, or durable, multi-layer silicone in coolant hoses. These details matter. A well-made part will not only fit better during installation but will also withstand the heat and pressure of high-performance driving, ensuring your Subaru STI upgrades deliver consistent and reliable power for years to come.

Ensure Parts Compatibility

Nothing stops a project in its tracks faster than a part that doesn’t fit. Before you click "buy," double- and triple-check that the component is designed for your STI’s specific model year and trim. The Subaru platform has seen many changes over the years, and a part for a 2008 STI might not work on a 2018 model. Compatibility goes beyond just physical fitment; it’s also about how a new part will function within your entire system. For example, installing larger injectors requires a fuel pump that can keep up and an engine tune that can properly control them. Always read the product description carefully and, when in doubt, contact the seller to confirm it’s the right choice for your build.

Find the Best Value for Your Budget

Building a high-performance engine involves a significant financial investment, so getting the best value for your money is crucial. "Best value" doesn't mean buying the cheapest part available. Instead, it means finding a balance between price, performance, and reliability. Prioritize your spending on the most critical components, like the turbocharger, fuel system, and engine internals. For other parts, you may find that a mid-range option from a reputable brand offers 95% of the performance of a top-tier part for a fraction of the cost. Do your research, read reviews, and look for performance parts that provide the function you need without breaking the bank.

Get It Installed and Tuned Right

Choosing the right parts is only half the battle; getting them installed and tuned correctly is what brings your build to life. Proper installation ensures every component works as designed, while a professional tune harmonizes all your new hardware, protecting your engine and maximizing performance. This final step is crucial for transforming a collection of high-quality parts into a reliable, powerful machine. Skipping or cutting corners here can lead to poor performance, or worse, catastrophic engine damage. Let's walk through how to ensure your upgrades are installed and calibrated perfectly.

Why a Professional Tune is Crucial

Think of your engine's computer (ECU) as its brain. When you install performance parts like a larger turbo or a full turbo-back exhaust, you're changing how your engine breathes and operates. Without an updated map, the ECU is still trying to run the old hardware, which can cause the engine to run lean, detonate, and ultimately fail. A professional tune recalibrates the ECU to account for these new parts. An expert tuner will adjust fuel delivery, ignition timing, and boost levels to create a safe and powerful setup. This is how you unlock the full potential of your Subaru STI upgrades, ensuring the engine produces more power reliably.

Understand Installation Requirements

Before you start turning wrenches, it’s important to understand what each installation entails. Some parts, like an air intake, are straightforward bolt-on modifications. Others, such as internal engine components or a new turbo, are far more complex and require a significant amount of time and expertise. It's also critical to plan your build path. Knowing your ultimate power goal from the start helps you select the right parts and avoid buying components you'll have to replace later. Remember that many performance mods can make your car less comfortable for daily driving by adding noise and vibration, so consider the trade-offs between a track monster and a street-friendly car.

DIY vs. Pro Install: What's Right for You?

Deciding between installing parts yourself or hiring a professional comes down to your mechanical skill, available tools, and the complexity of the job. If you're experienced and comfortable working on cars, handling bolt-on performance parts can be a rewarding and cost-effective project. However, for critical jobs like engine assembly or transmission work, a professional installer is your best bet. Reputable shops have the specialized tools and experience to get the job done right, often providing a warranty on their labor. This peace of mind is invaluable when you're dealing with the heart of your vehicle.

Essential Tools for a DIY Job

If you decide to tackle installations yourself, having the right tools is non-negotiable. Beyond a basic socket set, you'll need a high-quality torque wrench to tighten bolts to factory specifications—this is critical for preventing leaks and component failure. A sturdy floor jack and jack stands are essential for safely working underneath your car. For more advanced projects, you might need an engine hoist, specialized pullers, or diagnostic tools to read engine data. Investing in the proper equipment not only makes the job easier but also helps you avoid damaging your expensive new WRX upgrades or your vehicle.

Consider the Costs and Risks

Upgrading your STI for more power is exciting, but it’s a serious commitment that goes beyond just buying parts. Before you start, it’s crucial to think through the financial and practical implications. A well-planned project accounts for the total cost, potential warranty issues, insurance adjustments, and how modifications might affect your car’s future value. Thinking about these factors upfront will save you from headaches down the road and ensure your build is sustainable in the long run. Being prepared for the total investment—in time, money, and paperwork—is just as important as choosing the right turbo.

Budgeting for Different Upgrade Stages

Engine upgrades are a significant financial investment, and costs can add up quickly. While basic bolt-ons might only set you back a few hundred dollars, a complete engine build is a different story. A fully built motor with a stronger transmission can easily surpass $15,000. This includes major components like a closed deck block, a robust STi 6-speed transmission, and a high-performance turbo.

To make this more manageable, plan your build in stages. Start with foundational performance parts that provide a solid base, then build from there as your budget allows. Prioritize quality over quantity; it’s always better to buy one high-quality component than three cheap ones that could fail and cause catastrophic damage.

How Upgrades Affect Your Warranty

One of the biggest concerns for owners of newer STIs is the factory warranty. While the Magnuson-Moss Warranty Act protects you from a dealer voiding your entire warranty for a single modification, the reality is more nuanced. A dealer can deny a warranty claim if they can prove your aftermarket part caused the failure. Installing a cat-back exhaust is unlikely to cause an issue, but a custom engine tune or a larger turbo almost certainly will if you have an engine-related problem.

If you’re planning significant Subaru STI upgrades, it’s best to assume your powertrain warranty will be affected. This is why it’s so important to work with reputable shops and use reliable parts—once you modify, you and your builder are responsible for the engine’s health.

What to Tell Your Insurance Company

Modifying your engine isn't just a conversation for the forums; you also need to talk to your insurance provider. Any significant change from the factory engine should be reported to your insurance company. Failing to disclose modifications could give them grounds to deny a claim if you get into an accident. Your premium may or may not change, but transparency is essential for ensuring you’re properly covered.

Before you begin your build, call your agent and discuss your plans. Some companies offer specialized policies for modified vehicles, which might provide better coverage for your expensive new parts. It’s a simple step that protects your investment.

The Impact on Your Car's Resale Value

While you’re building your dream car, it’s easy to forget that you might want to sell it one day. Heavily modified cars can have a niche market, which can make them harder to sell and potentially lower their resale value compared to a stock example. Many potential buyers are wary of taking on someone else's project, unsure of the quality of the work or the parts used.

However, a well-documented build using high-quality parts from reputable brands can help retain value. Keeping meticulous records of every part installed, every service performed, and every tune applied shows prospective buyers that the car was built with care and expertise. Ultimately, most enthusiasts modify their cars for their own enjoyment, with the plan to keep them for the long haul.

Maintain Your Modified STI

Installing your new performance parts is just the first step. To protect your investment and ensure your STI runs reliably for years to come, you need to adapt your maintenance routine. More power means more stress on your engine and drivetrain components, so staying proactive is key. A modified engine requires a higher level of attention than a stock one, but with the right habits and schedule, you can enjoy the extra performance without the extra worry. This means paying closer attention to your car's behavior, adjusting your service intervals, and knowing how to spot potential issues before they become serious problems.

Think of it as building a stronger relationship with your car—one where you understand its needs and can respond accordingly. The factory maintenance schedule was written for a stock vehicle operating under normal conditions. Your modified STI is now a high-performance machine that operates outside of those original parameters. Ignoring this reality is a fast track to premature wear or even catastrophic failure. By creating a new maintenance baseline that accounts for your specific upgrades and driving style, you’re not just performing upkeep; you’re actively managing the health and longevity of your build. This diligence is what separates a reliable, high-powered STI from one that’s constantly in the shop.

Daily Care for a Modified Engine

Great maintenance starts with great daily habits. Always allow your engine to warm up properly before getting into boost; this gives the oil time to reach its optimal temperature and viscosity to protect vital components. Similarly, after a spirited drive, let the engine idle for a minute or two before shutting it off. This cool-down period helps prevent oil coking in the turbocharger, extending its life. Be diligent about using high-quality fuel and fluids, and check your oil level frequently—at least every other time you fill up with gas. Your daily care routine should reflect your build's purpose; a track car will require more intensive checks than a modified daily driver.

How to Monitor Your Engine's Health

Your senses are your first line of defense in monitoring your engine. Pay attention to how your STI sounds, feels, and even smells. Any new noises, vibrations, or unusual odors could be early warning signs. For more precise data, consider installing aftermarket gauges to track boost pressure, oil pressure, and air-fuel ratios. These tools provide a real-time look at your engine's vitals, allowing you to spot deviations from the norm immediately. After installing major Subaru STI upgrades, like a new turbo or exhaust, this monitoring is especially crucial to confirm everything is working together as intended with your tune.

Adjust Your Maintenance Schedule

The factory-recommended service schedule is designed for a stock vehicle. Once you start adding power, you need a more aggressive maintenance plan. A good rule of thumb is to cut the standard intervals in half. If the manual suggests an oil change every 6,000 miles, do it every 3,000. The same logic applies to spark plugs, transmission fluid, and differential fluid. Increased power puts more strain on every part of your drivetrain, so more frequent fluid changes and inspections are essential for longevity. Keep a detailed log of all your maintenance to stay organized and track your car's history.

Troubleshoot Common Issues

Modifications can introduce new behaviors to your car. It's important to learn the difference between a normal characteristic of your build and a symptom of a problem. For instance, many performance mods can add more noise and vibration, which is often normal. However, a sudden change in sound or a new, rhythmic clunk is not. Common issues on modified STIs include boost leaks from loose couplers, sensor malfunctions, or fueling problems. If you encounter an issue you can't diagnose, don't hesitate to consult a professional. A proper diagnosis from an expert who offers engine tuning services can save you time, money, and potential engine damage.

Stay Safe and Street-Legal

Building a high-performance STI is an exciting process, but it’s easy to get so focused on horsepower numbers that you overlook safety and legal requirements. A powerful car is only fun if you can actually drive it without constantly looking over your shoulder. This is about more than just following rules; it’s about building your car responsibly to ensure it’s reliable, predictable, and safe for you and everyone else on the road.

Before you go all-in on modifications, take a moment to think about the bigger picture. You’ll need to consider local emissions laws, what makes a car comfortable enough for daily driving, and how to properly prepare for a track day if that’s your goal. Keeping everything above board also involves something simple but crucial: good record-keeping. Documenting your build not only helps with troubleshooting and future upgrades but also proves invaluable for maintenance and resale. A smart, well-documented build is always more impressive than a reckless one.

Meet Emissions Standards

Depending on where you live, your STI will likely need to pass regular emissions tests. Major engine modifications, especially to the exhaust system, can easily cause your car to fail. While removing the catalytic converter is a common path to more power, it’s also a surefire way to fail an inspection. The good news is you don’t have to sacrifice performance to stay compliant. You can find a middle ground with a high-flow "sports catalytic converter" and a professional engine tune. This combination allows for better exhaust flow while still treating harmful emissions, helping you meet local standards without choking your engine’s potential.

Keep Your Build Legal for the Street

Turning your STI into a track monster is tempting, but many performance mods can make your car less comfortable for daily driving. Think about the added noise, vibration, and harshness that come with stiffer suspension, a loud exhaust, or a racing clutch. Beyond comfort, certain modifications like illegal lighting or extreme body kits can attract unwanted attention from law enforcement. The key is to strike a balance that fits your needs. Choose high-quality Subaru STI upgrades that enhance performance without turning your daily commute into a chore or a legal risk.

Prep Your Car for the Track

If you plan on hitting the track, your preparation needs to go beyond just adding power. The intense demands of track driving require a focus on safety and durability. While Subaru designed the 6-speed STI gearbox with motorsport in mind, other components need attention. Your top priorities should be upgrading your brakes with high-performance pads and fluid, choosing the right tires for the conditions, and ensuring your cooling system can handle the heat. Investing in the right performance parts will not only make you faster but will also keep your car reliable and safe lap after lap.

Why You Should Keep Detailed Records

As you modify your STI, keeping a detailed log of every change is one of the smartest things you can do. This record should include the part, brand, date of installation, and any relevant notes from the install or tune. As you increase your car's power, you will likely need to upgrade drivetrain parts to prevent them from breaking, and your records will help you track this progression. This logbook is incredibly useful for troubleshooting problems, planning future upgrades, and performing maintenance. It also adds significant value and provides peace of mind for a potential buyer if you ever decide to sell your car.

Related Articles

• The Ultimate Subaru Engine Upgrade Guide
• Best Engine Mods for STI: Power & Reliability
• 5 STI Performance Engine Upgrades for Max Power

Frequently Asked Questions

What's the best first modification for my STI? While it's tempting to go straight for power, the smartest first step is to define your goals. Once you have a clear plan, a great starting point is an Air Oil Separator (AOS). It doesn't add horsepower, but it's one of the most important reliability modifications you can make to protect your engine from oil contamination, setting a strong foundation for all future upgrades. If you're looking for sound and a small performance gain without needing an immediate tune, a cat-back exhaust is another excellent choice.

Do I really need a professional tune for minor upgrades? Yes, for almost anything that changes how the engine breathes. Parts like an intake, downpipe, or new turbocharger alter the air-to-fuel ratio, and running them without a proper tune is a major risk to your engine's health. The engine's computer needs to be recalibrated to account for the new hardware. The only common exceptions are a cat-back exhaust or an Air Oil Separator, which can typically be installed without adjusting the tune.

How much power can the stock STI engine handle before I need to build the motor? This is a common question, and the general consensus is that the stock engine internals are reliable up to around 350-400 wheel horsepower. Pushing beyond this range significantly increases the stress on the stock pistons and connecting rods, making a failure more likely. If your goals include power figures north of 400 WHP, you should budget for a fully built engine with forged internals to ensure long-term reliability.

Why is an Air Oil Separator (AOS) recommended so often? An AOS is crucial for the health of any turbocharged Subaru engine, stock or modified. Under boost, oil vapor from the crankcase can get into your intake system. This oil contaminates the air and fuel mixture, which effectively lowers your fuel's octane and can lead to detonation—a primary cause of engine failure. An AOS captures this oil vapor and returns it to the oil pan, ensuring only clean air enters your engine and protecting it from this harmful process.

Should I upgrade my brakes and suspension before adding a lot of power? Absolutely. Adding horsepower is only one part of creating a high-performance vehicle. Your car needs to be able to handle the extra speed safely and effectively. Upgrading your brake pads, fluid, and lines ensures you can stop reliably, while improvements to your suspension will help you put the power down and maintain control through corners. A balanced car that can handle, stop, and accelerate well is always more enjoyable and safer to drive than one that's just fast in a straight line.