The Expert Subaru Cylinder Head Buyer's Guide
You’ve added the intake, the exhaust, and maybe even a bigger turbo, but you've hit a hard performance wall. Your Subaru engine has more to give, but it just can't breathe. This is the moment serious builders look past simple bolt-ons and focus on the engine's core. Stock heads are designed for daily driving compromises, not the extreme demands of high horsepower. Making real power means upgrading the engine's entire respiratory system. This guide is your complete breakdown of the performance Subaru cylinder head—explaining what it is, how it works, and why it's the key to building serious, reliable horsepower.
Key Takeaways
- Choose heads based on your driving style: Performance cylinder heads are a fundamental upgrade that improves airflow to make more power. The best set for you is the one engineered for how you actually use your car, whether for daily driving, overlanding, or track days.
- Define your horsepower goal first: Before you shop, decide on a realistic power target. This helps you select heads with the right features, like CNC porting and durable valvetrain parts, ensuring your entire engine works together as a balanced and reliable system.
- Budget for the complete job, not just the parts: A successful upgrade includes the cost of professional installation, supporting mods like camshafts or a built block, and a final engine tune. Factoring in these costs from the start protects your investment and prevents costly failures.
What Makes a Cylinder Head "Race Spec"?
If you're serious about making big power with your Subaru, you'll eventually hit the limits of your stock components. That’s where race spec cylinder heads come in. Think of them as a fundamental upgrade for your engine's breathing system. These aren't just replacement parts; they are highly engineered components designed specifically for high-performance applications. Whether you're building a dedicated track car or a high-horsepower street machine, the goal of a race spec head is the same: to dramatically improve airflow, which in turn allows your engine to produce significantly more power and operate more efficiently at high RPMs.
Standard cylinder heads are designed to be a reliable compromise for daily driving, balancing performance, fuel economy, and emissions. Race spec heads throw that compromise out the window in favor of all-out performance. They are meticulously modified through processes like porting and polishing to create the smoothest, most direct path for air and fuel to enter the combustion chamber and for exhaust gases to exit. This optimization is what unlocks the next level of potential from your Subaru’s engine, turning a capable car into a true performance machine.
How They Create More Power
At its core, an engine is an air pump. The more air it can move, the more fuel it can burn, and the more power it can make. Cylinder heads sit on top of the engine block and control this entire process. They house the valvetrain—valves, springs, and camshafts—that lets the air-fuel mixture in and the exhaust out. Race spec heads are designed to perfect this function for high-stress environments like drag racing, time attack, or hill climbs. By optimizing the shape and size of the intake and exhaust ports, they allow the engine to breathe more freely, especially at higher RPMs where stock heads become a bottleneck. This improved airflow and combustion efficiency is critical for maximizing horsepower and torque.
Race Spec vs. Stock: What's the Difference?
The difference between a stock head and a race spec head is all about precision and purpose. A stock head is mass-produced for everyday reliability. A race spec head is a work of art, customized for maximum power. For example, our top-tier Outlaw cylinder heads are built for dedicated race cars aiming for over 700 horsepower. They feature hand-finished, race-specific porting, custom valve seats, and matched runners to ensure every cylinder performs identically. This level of detail, including blueprint assembly and flow sheet data, is what separates a high-performance build from the rest. It’s the difference between simply adding parts and engineering a complete, cohesive system designed to win.
Myths About Performance Heads: Busted
Two common myths can trip up even experienced builders. The first is that any performance head will work. This isn't true. The right cylinder heads must match your vehicle's purpose. A set designed for an all-out drag car will have massive ports that hurt low-end torque, making it miserable for a daily driver or an overlanding Crosstrek. You have to match the head to your specific horsepower goals and how you plan to use your Subaru. The second myth is that cylinder heads always need to be milled or resurfaced during an install. While they must always be checked for flatness by a professional to ensure a perfect seal, they don't always require milling. Unnecessary milling can alter the compression ratio and cause other issues, so it's a job best left to an expert's discretion.
Diagnosing Common Cylinder Head Issues
Before you can upgrade, you need to know the health of your current setup. Cylinder head issues can be subtle at first, but they often lead to catastrophic engine failure if ignored. Symptoms like overheating, mysterious coolant loss, or milky oil are your engine's cry for help, often pointing directly to a problem with its cylinder head or, more commonly, the head gasket. Recognizing these signs early is key to preventing a minor issue from turning into a complete engine rebuild. Paying attention to changes in your Subaru's performance and fluid levels will help you catch problems before they escalate, saving you time, money, and a whole lot of frustration down the road.
Symptoms of a Failing Cylinder Head
One of the most common signs of a failing cylinder head or gasket is a chronically overheating engine. This often happens because a breach in the gasket allows coolant to leak into the combustion chamber, where it's burned off and sent out the exhaust. You might notice your temperature gauge creeping up or find yourself constantly topping off the coolant reservoir with no obvious external leak. Another tell-tale sign is contaminated oil. If you check your dipstick and the oil looks milky or frothy, like a coffee-shop latte, it means coolant is mixing with your oil. This is a serious problem that compromises the oil's ability to lubricate, putting your entire engine at risk of seizure.
The Subaru Head Gasket Question: What You Need to Know
The Subaru head gasket is a topic of much discussion, and for good reason. A typical failure can result in coolant or oil weeping externally from the engine, but a more severe internal leak is what causes the most damage. If you see clouds of white smoke pouring from your exhaust, especially with a distinct sweet smell, that’s a classic sign that coolant is entering the cylinders. Addressing this isn't just about swapping a gasket; it's about ensuring the entire system is sound. A proper repair involves having a professional inspect the cylinder heads for flatness to guarantee a perfect seal and may require a complete engine tune to ensure everything runs correctly afterward, protecting your investment in high-quality performance parts.
Who Makes the Best Subaru Cylinder Heads?
When you start shopping for race spec cylinder heads, you’ll quickly notice a few names that stand out in the Subaru community. The "best" option really depends on your specific build, power goals, and budget. Some brands focus on creating versatile heads for street and track use, while others engineer components purely for competition. The key is to find a manufacturer that aligns with your performance targets and has a proven track record for quality and reliability.
Choosing the right heads is a major decision that impacts your engine's entire performance profile. It’s not just about peak horsepower; it’s about creating a balanced, durable, and responsive engine. We’ll look at a few of the top contenders in the market, including our own specialized packages, to give you a clear picture of what’s available. This will help you compare the different philosophies behind each design and find the perfect match for your Subaru WRX or STI.
Spotlight on Crawford Performance Heads
Here at Crawford, we engineer our cylinder head packages to deliver a precise balance of power, durability, and engine response. We offer three distinct levels—Rebel, Bandit, and Outlaw—each tailored for different stages of performance for Subaru WRX, STI, and BRZ/FRS models. Whether you're building a high-performance daily driver or a dedicated track car, our cylinder head packages are designed to maximize airflow and withstand extreme conditions. We also provide an essential inspection service to ensure every component meets our strict standards before it ever goes into your engine, giving you confidence in your build’s foundation.
Spotlight on IAG Performance Heads
IAG Performance is another well-respected name in the Subaru world, known for producing high-quality engine components. They are particularly recognized for their CNC ported race cylinder heads, which are engineered for serious competition builds. Their top-tier heads are designed to support massive power outputs, with some packages capable of handling up to 950 horsepower when paired with the right supporting modifications. For builders aiming for maximum power on the track, IAG offers a compelling and proven option that has been tested in countless high-stakes racing environments.
Other Top Brands to Consider
Beyond Crawford and IAG, you'll find other reputable manufacturers offering quality cylinder heads. Companies like Flatirons Tuning, for example, provide a wide variety of cylinder heads and valvetrain components, giving builders plenty of options to choose from. Having a diverse market is great for consumers, as it allows you to find a solution that fits very specific needs or budgets. Exploring these different brands can help you understand the full range of available technologies and approaches to head design, from multi-angle valve jobs to unique porting techniques.
AEM
While AEM is widely recognized for its high-performance cold air intake systems, their role in your engine's breathing is fundamental. An upgraded intake is often the first step in improving airflow, and AEM designs their systems specifically for Subaru models to maximize air velocity and volume. Pairing a high-flow intake with race spec cylinder heads ensures your engine gets the dense, cool air it needs to make consistent power. It’s a foundational part of a complete performance breathing system that works in harmony with your head and exhaust setup, making sure the entire path from filter to tailpipe is optimized for maximum efficiency.
Brian Crower
Brian Crower is a go-to name for the components that live inside your cylinder heads, especially camshafts and valvetrain kits. Their products are engineered to optimize valve timing and lift, which is critical for taking full advantage of ported heads. Installing a set of Brian Crower cams allows your engine to move more air at higher RPMs, directly translating the improved flow from your heads into more horsepower. For builders looking to create a reliable, high-revving engine for their WRX or STI, their valvetrain components are a trusted choice for unlocking the full potential of a cylinder head upgrade.
GSC Power Division
GSC Power Division specializes in valvetrain components built for the most demanding Subaru engines. If your goal is a dedicated track or race car, GSC is a brand you'll encounter frequently. Their camshafts and valve springs are specifically designed to handle the stress of sustained high-RPM use and extreme cylinder pressures. This focus on durability under racing conditions makes their parts ideal for builds where reliability at the limit is non-negotiable, ensuring your valvetrain can keep up with the rest of your high-performance setup when you're pushing your engine to its absolute maximum.
Kelford Cams
Kelford Cams has earned a stellar reputation for its precision-engineered camshafts. Their cam profiles are meticulously designed to improve power delivery across the rev range, not just at the peak. For Subaru builders, this means better throttle response and a wider, more usable powerband. Choosing the right Kelford cam profile to match your cylinder heads and turbo setup is key to creating a balanced and responsive engine, making them a favorite among tuners and professional builders who demand precise, predictable performance for street and track applications alike.
Manley Performance
Manley Performance is a giant in the world of high-performance engine internals, and their valves are a crucial component of any serious cylinder head build. When you're pushing for big power, stock valves can become a failure point. Manley's stainless steel and Inconel valves are engineered to withstand extreme heat and pressure, providing the durability needed to support high-horsepower applications. Upgrading to Manley valves is a smart investment for ensuring the long-term reliability of your race spec heads and protecting your entire engine. You can find these and other essential performance parts to complete your build.
Price vs. Performance: Finding the Best Value
The cost of race spec cylinder heads can vary widely, reflecting the level of engineering, materials, and labor involved. You might see prices start under $1,000 for basic or used items, while high-end, fully-built CNC ported heads from top brands can exceed $5,000. Most performance packages from reputable names fall in the $3,000 to $5,000 range. It’s important to view this as an investment in your engine’s reliability and potential. A cheaper head might save you money upfront, but a well-engineered one will provide better performance and greater peace of mind down the road.
Decoding Performance Tiers: Stage 1, Stage 2, and Rally Spec
You’ll often hear Subaru enthusiasts talk about being "Stage 1" or "Stage 2," but what do these terms actually mean? Think of them as general milestones for performance upgrades. Stage 1 is your starting point, typically involving an ECU tune and maybe an upgraded air intake to get a bit more power over the stock setup. It’s a great first step for waking up your engine. Stage 2 gets more serious, adding components like a full turboback exhaust and requiring a more aggressive tune to match the improved airflow. This is where you start pushing the limits of stock internals. When you're ready to go beyond that, you enter the realm of custom or "Rally Spec" builds. This level requires a holistic approach, upgrading core components like your cylinder heads, pistons, and rods to create a fully balanced and reliable high-horsepower engine. Choosing the right path depends entirely on your goals, whether you're enhancing a daily driver or building a dedicated track machine with our specialized performance parts.
What to Look For When Buying Performance Cylinder Heads
When you’re ready to invest in performance cylinder heads, you’ll find a lot of options on the market. The key is to look past the marketing claims and focus on the specific features that create real-world power, reliability, and efficiency. A high-quality cylinder head is more than just a casting; it’s a precisely engineered component where every detail matters. From the way air flows through its ports to the materials used in its construction, each element plays a critical role in your engine's performance. Choosing the right heads is one of the most impactful upgrades you can make, but it's also one of the most complex. This guide will walk you through the essential technical specifications to look for, helping you make an informed decision. We'll cover everything from the importance of CNC porting for maximizing airflow to the critical role of upgraded valvetrain components in maintaining reliability under pressure. Understanding these details will help you choose a set of heads that not only meets your horsepower goals but also provides the durability to handle the demands of spirited driving, whether on the street, track, or trail.
Engine and Model Compatibility
Not all Subaru engines are created equal, and neither are their cylinder heads. Before you even think about adding a set of heads to your cart, you need to know exactly what engine is in your car. The architecture of Subaru's engines has evolved significantly over the years, and parts are rarely interchangeable between different series or even model years. Choosing a head that isn't designed for your specific engine is a recipe for a very expensive paperweight. It’s crucial to confirm compatibility to ensure proper fitment, function, and to get the performance gains you’re paying for.
EJ vs. FA Series Heads (EJ20, EJ257, FA24)
The two most common engine families you'll encounter in performance Subarus are the EJ series and the more recent FA series. The EJ engines, like the EJ257 in the STI, have been the workhorse for decades and have a massive aftermarket following. The newer FA engines, such as the FA24 in the current WRX, feature modern technology like direct injection. These two engine families are fundamentally different, from their timing systems to their port designs. You cannot use EJ heads on an FA block or vice versa. When shopping, make sure you are looking specifically for parts designed for your engine code, whether you're building a classic STI or a brand new WRX.
DOHC vs. SOHC Configurations
Another key distinction is the camshaft configuration: Double Overhead Cam (DOHC) or Single Overhead Cam (SOHC). DOHC engines, standard in performance models like the WRX and STI, use two cams per head to operate the intake and exhaust valves independently. This design allows for better airflow and higher RPM capabilities, making it the standard for any serious performance build. SOHC engines, found in some non-turbo models like the Forester or Impreza, use a single cam per head. While reliable for daily driving, they don't offer the same performance potential. All true race spec heads are designed for DOHC applications, so if you have a SOHC engine, a DOHC swap would be a necessary first step for a high-horsepower build.
Matching Heads to Your Model Year (2002-Present)
Even within the same engine family, Subaru has made subtle changes over the years. A cylinder head for a 2005 STI might have slight differences from one for a 2018 STI, such as variations in casting or sensor provisions. Reputable manufacturers will always specify the exact model year range their heads are compatible with. It is absolutely critical to double-check that the heads you're buying are a direct fit for your vehicle's specific year. This attention to detail prevents installation headaches and ensures all your existing components will integrate correctly. Always verify the product description to confirm it matches your car before making a purchase.
Complete Packages vs. Individual Components
Once you've confirmed compatibility, you face another big decision: do you buy a complete, pre-assembled cylinder head package or source all the individual components yourself? A complete package from a trusted builder offers a proven combination of parts that are professionally assembled and ready to install. This route saves you the time and risk of matching valvetrain components yourself. On the other hand, buying individual parts gives you total control to create a fully custom setup, but it requires a deep understanding of how each component—from the valves to the camshafts—will work together.
Upgrading Sprockets, Seals, and Gaskets
A truly comprehensive cylinder head upgrade involves more than just the head itself. The valvetrain—valves, springs, retainers, and camshafts—must be able to handle the increased stress and RPM of a high-performance engine. This is where complete packages shine. At Crawford Performance, our cylinder head packages are engineered with perfectly matched components designed to work in harmony. This eliminates the guesswork and ensures every part is up to the task. Furthermore, a proper installation always requires fresh gaskets, seals, and often upgraded cam sprockets. A complete package ensures you have a reliable, professionally assembled system that's ready for a final engine tune to unlock its full potential.
Why CNC Porting and Airflow Matter
Think of your engine as a powerful air pump—the more air it can move, the more power it can make. CNC (Computer Numerical Control) porting is a precision machining process that reshapes and enlarges the intake and exhaust ports inside the cylinder head. This process removes casting imperfections and creates an optimized path for air to enter and exit the combustion chamber. The result is a significant improvement in airflow, which is fundamental to increasing horsepower and torque. When evaluating heads, look for details on the CNC porting process, as a well-executed port job is one of the most effective ways to get more performance from your Subaru engine.
Choosing the Right Valvetrain Components
The valvetrain—which includes valves, springs, retainers, and guides—is the engine's respiratory system, and it takes a beating in a high-performance build. Stock components are designed for factory power levels and can fail under the stress of higher RPMs and increased cylinder pressure. Upgraded valvetrain components are essential for reliability. Look for heads built with high-strength, oversized valves made from materials like stainless steel or Inconel, which resist heat and wear. Paired with stiffer valve springs and lightweight titanium retainers, these performance parts prevent valve float at high RPMs, ensuring your engine operates safely and makes consistent power.
How to Judge Material and Build Quality
In a high-output engine, cylinder heads are subjected to immense heat and pressure. That’s why the quality of the materials and the overall build are non-negotiable. Reputable manufacturers use high-grade aluminum alloys and employ rigorous quality control throughout the manufacturing and assembly process. Look for brands that have a proven track record in motorsports, as this demonstrates their products can withstand extreme conditions. Investing in well-engineered cylinder head packages from a trusted source ensures you get a product built for longevity and precision, giving you peace of mind when pushing your vehicle to its limits.
The Importance of Combustion Chamber Design
The shape of the combustion chamber has a direct impact on your engine’s efficiency and power output. This small, sculpted space is where the magic happens—the air-fuel mixture is compressed and ignited here. A well-designed chamber promotes a fast, complete burn, which extracts more energy from the fuel. This leads to more horsepower, better throttle response, and improved fuel efficiency. Performance heads often feature reshaped combustion chambers that are optimized to work with specific piston designs and improve flame travel. It’s a highly technical detail, but it’s one that separates a good cylinder head from a great one.
What Is a Multi-Angle Valve Job (and Why You Need One)
A multi-angle valve job is a machining technique that dramatically improves airflow around the valve head. Instead of cutting a single 45-degree angle where the valve seals against the head (the valve seat), a machinist cuts three, four, or even five different angles. This creates a smoother, more contoured path for air and fuel to flow past the valve. The result is better low-lift airflow, which improves throttle response and torque, and a more secure seal when the valve is closed. This level of detail is a hallmark of high-quality performance heads and is crucial for anyone serious about maximizing their engine’s potential.
Match Your Cylinder Heads to Your Goals
Choosing the right race spec cylinder heads is less about finding the "best" ones and more about finding the right ones for your specific build. A set of heads that works wonders on a 900-horsepower drag car will feel sluggish and unresponsive on a daily driven WRX. The key is to define your goals first—for power, application, and budget—and then select the components that will get you there. This approach ensures you’re not just buying expensive parts, but making a smart investment in your Subaru’s performance.
Think of it as creating a recipe for your engine. You wouldn't use the same ingredients for a quick street snack as you would for a full-course competition meal. By matching the heads to your goals, you ensure every component works in harmony to deliver the driving experience you’re after, whether you're carving up backroads or chasing lap times.
How Much Horsepower Do You Really Want?
Your horsepower target is the single most important factor in selecting cylinder heads. The ability of a head to flow air is directly tied to its power potential. For example, heads designed for serious racing offer a significant improvement in airflow, which is essential for making big power at high RPMs. If your goal is a modest 400hp for a spirited street car, you won't need the same aggressive porting and oversized valves as someone aiming for 700hp.
Start by being realistic about your power goals. This will help you narrow down the vast selection of performance parts and focus on heads that are engineered for your target range. Over-speccing your heads can hurt low-end torque and drivability, while under-speccing will create a bottleneck that chokes your engine’s potential, no matter what other mods you have.
Street vs. Track: What Do You Need?
How you plan to use your Subaru dramatically changes your needs. A street car requires a broad powerband with good response for daily driving, while a dedicated track car is all about maximizing peak power. The ideal heads for a daily driver will prioritize air velocity to maintain torque, while track-focused heads will be ported for maximum airflow, even if it sacrifices some low-end performance. This is a critical distinction that impacts everything from valve size to camshaft selection.
If you’re unsure which package is right for your car, it’s always best to consult an expert. The team here at Crawford Performance can help you weigh the pros and cons of different setups for your specific model, whether it's a Subaru WRX or a Forester. A quick conversation with a professional builder can save you from making a costly mistake and ensure your setup is perfectly matched to your driving style.
Planning for Essential Supporting Mods
Cylinder heads are a team player; they can’t achieve their full potential alone. To reach significant power levels, you need to pair them with the right supporting modifications. For instance, if you want to make 500 horsepower or more at the wheels, you’ll likely need to add aggressive components like GSC S2 Camshafts and Kelford DLC Coated Lifters. These parts are designed to work with high-flowing heads to optimize the engine’s breathing at high RPM.
Beyond the valvetrain, consider the rest of your engine. A built short block, an upgraded turbocharger, a high-flow fuel system, and a less restrictive exhaust are all necessary pieces of the puzzle. Upgrading your cylinder heads is a major step, so make sure the rest of your build is ready to support the increased power and airflow. Planning these STI upgrades together ensures a balanced and reliable setup.
How to Budget for Your Cylinder Head Upgrade
It’s important to be realistic about the costs involved in a cylinder head upgrade. Prices for cylinder heads can range widely, from under a thousand dollars for a basic set to over $5,000 for fully-built, race-ready options. Your budget will largely dictate the performance ceiling of your build, so it’s crucial to plan accordingly. Remember that the heads themselves are just one part of the total cost.
When creating your budget, be sure to factor in gaskets, head studs, supporting valvetrain components, labor for installation, and—most importantly—a professional tune. Engine tuning services are non-negotiable after this kind of work to ensure the engine runs safely and efficiently. Skimping on any of these areas can lead to catastrophic failure, turning your dream build into a very expensive paperweight.
Calculating the Total Cost: Parts and Labor
The price of the cylinder heads themselves is only the starting point. To do this job right, you need to budget for the entire project. This includes essential supporting parts like new head gaskets, high-strength head studs, and potentially other valvetrain components that should be replaced at the same time. Professional installation by a technician experienced with Subaru engines is also a major factor. Finally, and this is non-negotiable, you must account for a professional tune. After changing how your engine breathes, its fuel and timing maps need to be completely recalibrated. Skipping the engine tuning services is the fastest way to turn your investment into a pile of scrap metal.
Cost-Saving Alternatives: Rebuilding and Open-Box Parts
If a brand-new set of fully-built heads isn't in the budget, you still have options. Rebuilding your existing cylinder heads can be a cost-effective route, provided the original castings are in good condition. This involves sending them to a reputable machine shop for inspection, cleaning, and performance work like porting and installing upgraded valvetrain components. Another alternative is sourcing quality used or open-box parts. The key here is caution—always buy from a trusted seller and have the heads professionally inspected for flatness, cracks, or other damage before installation. These routes can save you money on the initial purchase, but remember that professional labor and a final tune are still essential costs for protecting your engine.
Installing Your Cylinder Heads: The Right Way
Getting a set of high-performance cylinder heads is a major step, but the real magic happens during installation. This isn't a job you can rush. Precision and attention to detail are what separate a successful build from a frustrating and expensive failure. Taking the time to follow the correct procedures ensures your new heads deliver the power and reliability you expect. From the initial prep work to the final tune, each step builds on the last to create a solid foundation for your engine's performance.
Your Pre-Installation Checklist
Before a single bolt is turned, proper preparation is essential. Start by making sure your workspace and all components are impeccably clean. Any debris, old gasket material, or grime can compromise the seal and lead to serious problems. Once the block surface is spotless, carefully inspect your new cylinder heads for any signs of damage that may have occurred during shipping. Lay out all your new gaskets and hardware. As a crucial final step, apply a light coat of clean engine oil to the threads and washers of your head bolts. This simple action ensures accurate torque readings and prevents the threads from galling under pressure.
Why Critical Measurements Can't Be Skipped
Never assume a part is perfect right out of the box. Even brand-new cylinder heads should be checked for flatness with a precision straight edge and feeler gauge. While heads don't always need to be milled, they must be verified as perfectly flat to guarantee a proper seal with the head gasket. A warped surface, even one that's invisible to the naked eye, can create a weak spot that leads to coolant leaks or a blown gasket down the road. This is a critical measurement that protects your entire investment, so have it checked by a professional if you don't have the tools.
Getting the Torque Sequence Right
Torquing your head bolts is a science, not a guessing game. Every Subaru engine has a specific, multi-step sequence for tightening the bolts, which is designed to apply pressure evenly across the entire head. You can't just tighten them in a circle. Following the factory-recommended pattern and torque specifications is vital to prevent warping the cylinder head or creating uneven stress on the block. For example, a common sequence involves tightening all bolts to 22 ft-lbs, then to 51 ft-lbs, and finally turning them an additional angle. Always consult a reliable service manual for your specific Subaru model to get the exact procedure right.
The Correct Engine Break-in Procedure
Once your engine is reassembled, the work isn't over. A proper engine break-in procedure is critical for seating the new piston rings, bearings, and valvetrain components correctly. The first few hundred miles are the most important for the long-term health of your build. This typically involves varying the engine RPM, avoiding constant speeds, and refraining from heavy acceleration or high-RPM pulls. An effective break-in ensures all the new components wear in together smoothly, creating strong seals and minimizing friction for maximum performance and longevity. Skipping this step can undo all your hard work.
Why Post-Installation Tuning Is a Must
Installing performance cylinder heads fundamentally changes how your engine breathes. The improved airflow means your engine’s original fuel and ignition maps are no longer accurate. To get the most out of your upgrade and ensure your engine runs safely, a professional tune is non-negotiable. The best way to dial everything in is to get the car on a dynamometer for a few pulls. Expert engine tuning services will adjust the ECU parameters to match the new airflow characteristics, optimizing performance and preventing lean conditions that could lead to catastrophic engine damage.
Solving Common Installation Challenges
Installing race spec cylinder heads is a major upgrade, and doing it right is non-negotiable. Even the best heads won't perform correctly if the installation is sloppy. A few common hurdles can trip up even experienced DIYers, but with a bit of foresight, you can handle them like a pro. Paying close attention to clearance, hardware integrity, alignment, and cooling will protect your investment and ensure you get the power you paid for. Let's walk through the most critical challenges and how to address them head-on.
How to Check Piston-to-Valve Clearance
This is one of the most crucial steps in any performance engine build. When you install heads that have been machined or have aggressive camshafts, the space between your pistons and valves can shrink. If they get too close, they can collide, leading to catastrophic engine failure. You must physically check the piston-to-valve clearance to confirm it’s within safe limits. Don't just assume it's fine. This measurement gives you the peace of mind that your valvetrain will operate without interference, protecting your engine from self-destruction under high RPMs.
Are Your Head Bolts Up to the Task?
Your cylinder head bolts are under immense pressure, containing thousands of pounds of combustion force. Over time, the constant heat cycles and stress can cause them to stretch and weaken. Reusing old bolts is a gamble you don't want to take. For a secure seal and reliable performance, always use new, high-quality head bolts or studs. Following the correct torquing sequence is just as important. This ensures the clamping force is distributed evenly across the head gasket, preventing leaks and ensuring your heads stay put. Investing in quality performance parts here is essential for a durable build.
Tips for Perfect Head Alignment
Properly aligning and torquing your cylinder heads is key to a perfect seal and optimal performance. An uneven installation can warp the heads and cause gasket failure down the road. The right method involves a specific sequence to apply even pressure. A proven technique for Subarus is to first torque all bolts to 22 ft-lbs, then increase to 51 ft-lbs. After that, you loosen all bolts in the reverse order of tightening before applying the final torque specs. This multi-step process helps the head and gasket settle properly, creating a reliable seal that will hold up under pressure.
Does Your Cooling System Need an Upgrade?
Race spec heads are designed to make more power, which also means they generate more heat. Your stock cooling system might not be up to the task of keeping temperatures in check. Before installation, make sure all cooling passages in the engine block and heads are completely clear of debris or blockages. Overheating is the enemy of aluminum heads, as it can cause them to warp and lead to serious engine damage. Consider upgrading your radiator or other cooling components to handle the increased thermal load. Proper engine tuning services are also critical to dial everything in and manage temperatures effectively.
Maintaining Your Heads for Long-Term Performance
Upgrading to race spec cylinder heads is a significant investment in your Subaru's power and potential. But the work doesn't stop after the installation. To protect that investment and ensure your engine delivers consistent, reliable power for years to come, you need a solid maintenance plan. High-performance parts are subjected to greater stress, heat, and pressure than their stock counterparts, making diligent upkeep absolutely essential.
Think of it less as a chore and more as part of the performance lifestyle. Regular inspections and proactive care will help you catch small issues before they escalate into catastrophic failures. A well-maintained engine not only performs better but also gives you the confidence to push your vehicle, whether you're on the track, the trail, or the street. By staying on top of a few key areas, you can enjoy the full benefits of your upgraded heads and keep your engine running strong.
Your Regular Inspection Checklist
Regular check-ins with your engine are the best way to spot trouble early. Pay close attention to head gasket integrity, as this is a common failure point in modified Subaru engines. Look for any signs of oil or coolant weeping from where the cylinder head meets the engine block. Another critical area is the cooling system. Ensure your cooling channels are free of blockages or buildup, because even minor overheating can cause an aluminum cylinder head to warp, leading to serious damage. A simple visual inspection during routine fluid checks can save you a massive headache down the road.
When Should You Service Your Heads?
While there’s no universal schedule that fits every build, your service intervals should reflect how you use your car. A track-focused STI will require much more frequent checks than a daily-driven Forester with mild performance parts. The most important service is the one that happens first: professional installation. Many manufacturers require it to validate the warranty, so this isn't the place to cut corners. After that, stick to a strict schedule of high-quality oil changes and coolant flushes. These basic services are your first line of defense in protecting the intricate components within your new cylinder heads and maintaining optimal engine health.
How to Monitor Engine Performance
Keeping tabs on your engine’s output is key to knowing if your heads are performing as they should. The most accurate method is to get the car on a dynamometer. Regular dyno pulls provide concrete data, allowing you to track horsepower and torque over time and spot any downward trends. Beyond the dyno, trust your senses. Listen for any new or unusual noises from the engine bay, and be alert to any noticeable loss of power or responsiveness. A well-calibrated "butt dyno" combined with a watchful eye on your temperature and pressure gauges can tell you a lot about your engine's condition.
Warning Signs to Watch For
Your Subaru will almost always give you signs when something is wrong with the heads. White, sweet-smelling smoke from the exhaust is a classic indicator of a coolant leak into the combustion chamber. Milky, frothy oil on your dipstick means coolant and oil are mixing—a tell-tale sign of a blown head gasket. If you ever have the heads serviced, insist on new head bolts. The old ones have been through countless heat cycles and can't be trusted to torque properly again. Following the correct torquing sequence is non-negotiable for a reliable seal and long-term performance.
How to Make a Smart Purchase
Upgrading your cylinder heads is a serious investment in your Subaru’s performance. It’s not just about picking a part off a shelf; it’s about making a strategic decision that will affect your engine’s power, reliability, and longevity. To get the best return on your investment, you need to think through the entire process, from balancing your budget to planning for installation. A smart purchase means looking beyond the initial price tag and considering the total value, including performance gains, durability, and the support you get from the manufacturer. Let’s walk through the key factors that will help you make a confident and informed choice for your build.
How to Balance Quality and Cost
When you start shopping for race-spec cylinder heads, you'll notice a wide price range, from under a thousand dollars for basic options to over $5,000 for fully-built, high-performance packages. This difference isn't arbitrary—it reflects the quality of materials, the precision of the CNC porting, the caliber of the valvetrain components, and the engineering behind the design. While a lower price might be tempting, it’s important to remember that cylinder heads are critical to your engine's health. Opting for a well-engineered set of heads from a reputable brand ensures you’re getting a product that can handle the stress of increased power and RPMs, giving you reliable performance on the track or trail.
Understanding Warranty Coverage
A manufacturer’s warranty is a direct reflection of their confidence in their product. For a high-stress component like a performance cylinder head, a solid warranty provides crucial peace of mind. For example, at Crawford Performance, we stand behind our engine builds with a 12-month/12,000-mile warranty. When you see a company offering this kind of protection, it signals that their parts are built to last. Before you buy, always read the fine print. Understand what the warranty covers, its duration, and any conditions that might void it, such as requiring installation by a certified professional. This protection is an essential part of your investment.
Don't Forget the Cost of Supporting Upgrades
Race-spec cylinder heads don't work in isolation; they are part of a complete engine system. To unlock their full potential, you need to plan for supporting modifications. High-flow heads will demand more air and fuel, which may require upgrading your intake manifold, injectors, fuel pump, and exhaust system. More importantly, the increased power puts more strain on your engine's bottom end. To handle the new capabilities of your heads, you might need a built short block. A crucial final step is a professional tune to synchronize all the new components. Proper engine tuning services ensure your engine runs safely and efficiently, maximizing the gains from your new heads.
Why Professional Installation Matters
While many Subaru owners are skilled DIY mechanics, installing performance cylinder heads is a job best left to the experts. The process requires specialized tools, meticulous measurements, and a deep understanding of Subaru engines. A small mistake, like an incorrect torque sequence or improper head gasket alignment, can lead to major engine damage. Furthermore, many manufacturers require installation by a certified technician to keep the warranty valid. Investing in professional installation protects your new parts, ensures everything is assembled to exact specifications, and guarantees you’ll get the reliable, high-end performance you paid for. It’s the final step in making a truly smart purchase.
Related Articles
Frequently Asked Questions
Can I install race spec heads on my otherwise stock Subaru engine? While you technically can, you won't see the benefits you're paying for. High-performance heads are designed to work as part of a complete system. On a stock engine, they will outflow the factory intake, turbo, and fuel system, meaning those components will become the new bottleneck. To truly take advantage of the upgrade, you need to pair the heads with supporting modifications that can keep up with the increased airflow.
Will high-performance heads make my car unreliable for daily driving? Not if you choose the right ones for your goals. A set of heads engineered for an all-out race car will certainly compromise low-end torque and make street driving less enjoyable. However, many performance heads are designed specifically for high-performance street cars. When matched correctly to your power goals and paired with a professional installation and tune, they can improve power and response without sacrificing the reliability you need for daily use.
What's the main difference between a mid-range and a top-tier set of cylinder heads? The difference comes down to the level of precision, materials, and engineering involved. A top-tier set will typically feature more extensive CNC porting for maximum airflow, superior valvetrain components made from materials like Inconel or titanium to handle extreme heat and RPM, and meticulous hand-finishing. This level of detail allows the engine to support significantly higher horsepower levels safely and operate more efficiently under the intense stress of racing conditions.
How do I know when it's time to upgrade my cylinder heads? You've likely reached the limit of your stock heads when your engine's power gains start to level off, even after upgrading other major components like the turbocharger and fuel system. A classic sign is when the engine feels like it's struggling to breathe and runs out of steam in the upper RPM range. If you're building an engine to handle significant power, upgrading the heads becomes a foundational step to prevent them from being the primary restriction.
Is a professional tune really necessary after installing new heads? Yes, it is absolutely essential and not a step you can skip. Performance cylinder heads fundamentally alter how your engine breathes, and the factory ECU is not programmed to manage this increased airflow. A professional tune adjusts the fuel and ignition timing to match the new characteristics of your engine. Without it, you risk running a dangerously lean air-fuel mixture, which can lead to detonation and catastrophic engine damage.