FA20 Short Block: Your Complete Upgrade Guide

There's a certain anxiety that comes with pushing a stock engine to its limits. Every time you go for a spirited drive or a lap at the track, a small part of you might wonder if this is the time something lets go. Upgrading your engine's core is about more than just chasing horsepower; it's about replacing that anxiety with confidence. A professionally built FA20 short block provides the peace of mind that comes from knowing your engine's internals are prepared for the power you're making. It’s the key to unlocking your car’s true potential without the constant fear of catastrophic failure.

Key Takeaways

• Prioritize a Built Block for Reliable Power: The stock FA20 engine has its limits. To safely exceed 350 horsepower, upgrading to a short block with forged internals is the essential first step for building a durable, high-performance engine.
• Budget for Supporting Mods and a Tune: A built short block is only one piece of the puzzle. Your build requires essential upgrades to the fuel and cooling systems, and a professional tune is critical to ensure all components work together safely and effectively.
• Match the Build to Your Goals and Commit to Maintenance: Define your target horsepower and driving style before you buy to avoid overspending or underbuilding. Once installed, protect your investment with a strict break-in period and a consistent maintenance schedule, including frequent oil changes.

What is an FA20 Short Block?

Think of an FA20 short block as the heart of your engine build. It’s a partially assembled engine that includes the engine block itself and the core rotating components inside: the crankshaft, connecting rods, and pistons. It doesn't include the cylinder heads, camshafts, or other external accessories like the intake manifold or turbocharger. This makes it the perfect foundation for anyone looking to build a high-performance engine for their Subaru WRX (2015-2021) or BRZ.

Upgrading to a built short block means you’re replacing the factory bottom end with a foundation engineered to handle significantly more power and stress. It’s the starting point for a truly custom setup. This approach gives you the flexibility to select your own cylinder heads and supporting performance parts to create an engine package perfectly tailored to your goals. Whether you're building a high-horsepower track car or a reliable daily driver with some extra punch, starting with a solid short block is the right way to do it.

Breaking Down the Core Components

The real magic of a built FA20 short block lies in its upgraded internals. While a stock engine uses cast pistons and weaker connecting rods, a performance short block features much stronger, forged components. Forged pistons and connecting rods are manufactured under extreme pressure, creating a denser and more resilient molecular structure. This allows them to endure the intense heat and higher cylinder pressures that come with Subaru WRX upgrades like a larger turbo and an aggressive tune. This added strength is what gives you the confidence to push for more power without risking engine failure.

Short Block vs. Stock vs. Long Block

Your stock FA20 engine is perfectly capable for daily driving at factory power levels. However, its internal components were not designed to handle the stress of major performance modifications. When you start adding significant power, you’ll quickly reach the limits of the stock hardware. A built short block solves this by providing a durable foundation for you to build upon, giving you the freedom to complete the engine with your choice of heads and cams. A long block takes this one step further; it’s a more complete assembly that includes the short block plus the cylinder heads and valvetrain, often arriving ready to install. A long block is an excellent choice for those who want a proven, pre-assembled package with less guesswork.

Why Upgrade to a Built FA20 Short Block?

The stock FA20 engine in your Subaru is a fantastic piece of engineering, but it has its limits. When you start pushing for more power with bolt-ons and a tune, you quickly approach the threshold of what the factory components can safely handle. This is where a built short block comes in. Upgrading isn't just about chasing massive horsepower numbers; it's about building a reliable foundation that can support your performance goals without compromise. A built FA20 short block replaces the stock internals—pistons, connecting rods, and crankshaft—with high-strength, forged components designed to withstand the increased stress from higher boost and more aggressive tuning.

It’s the single most important step you can take to transform your car from a fun daily driver into a true performance machine. This upgrade gives you the confidence to push the limits on the street or the track, knowing your engine's core is up to the task. By investing in a stronger foundation, you're not just enabling more power; you're ensuring the entire system works in harmony. This allows other Subaru STI upgrades to perform at their peak, creating a balanced and dependable build. Ultimately, a built short block is about unlocking your car's potential safely and sustainably.

Handle More Power and Gain Performance

This is the most common reason drivers upgrade. A stock FA20 engine is generally safe up to around 350 horsepower, but pushing beyond that is a gamble. A professionally built FA20 short block completely changes the game. It’s engineered to reliably handle 400-450 horsepower for daily driving and track use, providing a solid foundation for serious performance. With additional supporting mods like an upgraded fuel system and a larger turbo, that same block can push well beyond 600 horsepower. This upgrade unlocks the true potential of your vehicle, allowing you to install the performance parts you need to achieve your goals without worrying if your engine's core can keep up.

Built for Superior Reliability and Durability

Power is nothing without reliability. Over two decades of testing and racing Subaru engines has taught us exactly where the stock components fail and at what power levels. We use that knowledge to engineer built short blocks that are significantly stronger than factory units. By replacing weaker cast pistons and connecting rods with robust forged alternatives, we create an engine that can endure the intense heat and pressure of high-performance driving. This isn't just about preventing catastrophic failure; it's about building an engine that delivers consistent performance lap after lap. When you invest in a quality built block, you're investing in durability and the peace of mind that comes with knowing your engine is prepared for anything you throw at it, from daily commutes to demanding Subaru WRX upgrades.

Common Myths About Built Engines, Busted

Let's clear up a few things. A common myth is that built engines are fragile and only suited for the track. This couldn't be further from the truth. A properly assembled built FA20 is designed to handle significantly more power and stress than a stock engine, making it more reliable when tuned correctly. On the flip side, some believe a built short block is indestructible. While incredibly robust, it's not bulletproof. A high-performance engine is a complete system, and its longevity depends on proper installation, supporting modifications, and professional engine tuning services. Neglecting these critical steps is often the real cause of failure, not the block itself.

Who Makes the Best FA20 Short Blocks?

When you’re ready to invest in a built short block, choosing the right builder is the most critical decision you’ll make. The market has several reputable names, and the "best" one often comes down to your specific power goals, budget, and trust in the builder's experience. A quality short block is the foundation of a powerful and reliable engine, so it pays to understand what sets the top manufacturers apart. We’ll look at what makes a great short block, from design philosophy and materials to the fine details of craftsmanship that ensure your engine can handle the power you throw at it.

The Crawford Performance Advantage

With over two decades of experience pushing Subaru engines to their limits, we've learned exactly where stock components fail and how to engineer solutions that last. This deep understanding is built into every one of our short blocks. We don't just assemble parts; we re-engineer them. Our proprietary piston design, for example, is engineered to improve engine efficiency and lower internal pressure, allowing you to make more power safely at the same boost levels. This focus on proven engineering and rigorous testing is why a Crawford Performance Built Short Block is trusted for both high-performance street cars and competitive track builds.

Comparing Other Top Manufacturers

While we stand firmly behind our engines, it’s helpful to know the landscape. Other respected builders like IAG Performance also offer a range of FA20 short blocks tailored to different power targets. They are well-regarded in the community, particularly for their staged blocks that cater to various builds, from mild street upgrades to serious track applications. Companies like these have earned their reputation by consistently delivering reliable engines. Doing your research on different builders helps you appreciate the subtle differences in philosophy and component choice, ensuring you find the perfect match for your project’s specific needs and performance goals.

What to Look For: Quality, Materials, and Craftsmanship

Regardless of the manufacturer, a top-tier built short block shares a few key characteristics. Always look for forged pistons and connecting rods, as these are essential for withstanding the higher temperatures and cylinder pressures of a modified engine. The quality of the machine work and assembly is just as important as the parts themselves—precise clearances and tolerances are what separate a reliable engine from a ticking time bomb. The final price is often a direct reflection of the block’s power rating and the quality of its performance parts. A higher-rated block will use more robust components, which naturally comes with a higher cost.

How Much Power Can an FA20 Short Block Handle?

One of the first questions every enthusiast asks is, "How much power can it take?" The stock FA20 engine is impressive, but it has its limits, particularly when you start adding significant horsepower. When you’re ready to move past those factory constraints, a built short block is the foundation for making serious, reliable power. The exact horsepower an FA20 can handle depends entirely on the quality of the internal components, the precision of the assembly, and your specific performance goals.

With the right combination of parts and precise tuning, the FA20 transforms from a capable street engine into a high-performance powerhouse. We've seen these engines handle everything from spirited daily driving at 400 horsepower to all-out track builds pushing well beyond 600. It all comes down to choosing the right components for your desired power level and intended use. Let’s break down what you can expect at different stages.

The Sweet Spot: 400-450 HP for Daily Driving

For most drivers, the sweet spot for a built FA20 is in the 400-450 horsepower range. This level provides a massive performance gain over stock, making your car incredibly fun for daily driving and occasional track days without sacrificing reliability. A well-built engine can comfortably handle this power output day in and day out. This is the perfect target for the enthusiast who wants a fast, responsive car that’s still practical enough for the daily commute. It’s a popular goal for many Subaru WRX owners who want to unlock their car’s true potential without creating a vehicle that's too aggressive for the street.

Pushing the Limits: 600-800 HP for the Track

If your ambitions are set on competition or creating a dedicated track monster, the FA20 is more than capable of rising to the challenge. Pushing into the 600-800 horsepower range requires a top-tier build with premium forged internals and meticulous assembly. This isn't just about the short block; at this level, every supporting component becomes critical. You'll need a robust fuel system, a larger turbo, and an upgraded cooling system to manage the increased stress and heat. Most importantly, achieving these numbers safely requires precise engine tuning services from an expert who can dial in every parameter perfectly for maximum performance and safety.

Match the Engine to Your Power Goals

A built short block is not a one-size-fits-all solution. The components required for an 800-horsepower race engine are very different from those needed for a 450-horsepower street build. Several critical factors determine the final specifications of a built short block, and the biggest driver is the power rating. A block designed for 800 horsepower will have different pistons and connecting rods compared to one designed for 600 horsepower. Be realistic about your goals and budget. Overbuilding for power you'll never use adds unnecessary cost, while underbuilding is a surefire way to cause catastrophic engine failure. Carefully consider all the performance parts that will work together to achieve your goal.

How Much Does an FA20 Short Block Cost?

When you're planning a build, the budget is always a top consideration. The cost of a built FA20 short block isn't a one-size-fits-all number; it varies based on your power goals, the components used, and other factors like core charges. Let's break down what you can expect to invest in this foundational upgrade for your Subaru.

Price Ranges by Power Level

The single biggest factor determining the price of a built short block is its power rating. Simply put, a block engineered to handle 800 horsepower will require more robust—and therefore more expensive—internal components than one designed for 450 horsepower. Think forged pistons, stronger connecting rods, and a meticulously balanced crankshaft. As you shop for performance parts, you'll see that prices scale with capability. A block for a reliable daily driver with moderate power goals will be the most accessible, while a competition-ready engine built for the track represents a more significant investment in durability and raw power.

Understanding Core Charges and Wait Times

When you see the price tag on a short block, you might also notice a "core charge." Don't let it surprise you—it's standard practice in the industry. Think of it as a deposit. You pay this fee upfront, and once you send your old, usable engine block back to the builder, you get that money refunded. This system encourages recycling and helps keep costs down for everyone. It's a crucial detail to factor into your total budget. Also, remember that these engines are often built to order. Quality craftsmanship takes time, so plan for potential wait times when scheduling your build.

Is It Worth the Investment?

A built FA20 short block is a serious investment, but it's the bedrock of any high-horsepower Subaru build. While the stock engine is capable, it has its limits. Pushing past them without reinforcing the engine's core is a recipe for disaster. Investing in a built block gives you the peace of mind to chase bigger power numbers reliably. To truly get your money's worth, remember that the short block is just one piece of the puzzle. It needs to be paired with the right supporting modifications and professional engine tuning services to create a balanced, powerful, and durable machine that delivers on its potential.

What Other Mods Will You Need?

Dropping a built FA20 short block into your Subaru is a massive step toward your performance goals, but the work doesn’t stop there. Think of the short block as the powerful new heart of your car; it needs an equally capable circulatory and respiratory system to support it. Simply installing the block without upgrading the surrounding components is a recipe for disappointment and potential engine damage. To truly get the most out of your investment and ensure your build is reliable, you need to address the systems that fuel, cool, and manage that newfound power.

These supporting modifications aren't just suggestions—they are essential pieces of the puzzle. From the fuel pump to the radiator to the final ECU tune, each component plays a critical role in creating a cohesive, high-performance machine that you can drive with confidence, whether you’re on the street or the track. Let’s walk through the key systems you’ll need to upgrade to complete your build.

Fueling Your Power: Essential System Upgrades

More power demands more fuel. It’s a simple equation. As you increase airflow with a larger turbo and a more capable engine, your fuel system must keep pace to maintain a safe air-to-fuel ratio. A built FA20 can reliably handle 400-450 horsepower on the stock direct injection system, which is impressive for daily driving and light track use. However, if your goals are set higher than that, you’ve reached the limit of the factory setup.

To push past 450 HP, you’ll need to add a secondary fuel system, like port injection. The stock direct injectors simply can’t flow enough fuel to support bigger power numbers safely. Upgrading your fuel pump and injectors ensures your engine never starves for fuel under heavy load, protecting it from catastrophic failure and unlocking its true potential. These performance parts are the foundation of a reliable high-horsepower build.

Keeping it Cool: Turbo and Cooling Requirements

Heat is the enemy of performance and longevity. A built engine making significantly more power than stock will also generate a lot more heat, and the factory cooling system isn’t equipped to handle it. The engine block is just one part of a larger system that includes your turbo, radiator, and oil cooler, all of which need to work together to manage temperatures. Overlooking this step can quickly lead to overheating, which can be fatal for any engine, built or not.

To protect your investment, upgrading your cooling system is non-negotiable. Installing a high-performance radiator, a lower-temperature thermostat, or a dedicated oil cooler will help dissipate the extra heat effectively. These Subaru WRX upgrades ensure your engine operates within a safe temperature range, even during aggressive driving, preserving its health and giving you consistent performance lap after lap.

The Final Touch: Engine Management and a Pro Tune

After all your new hardware is installed, you need to get every component talking to each other correctly. This is where engine management and a professional tune come in. A pro tune is the final, critical step that harmonizes your entire build. A tuner will recalibrate your vehicle’s ECU, adjusting crucial parameters like fuel delivery, ignition timing, and turbo boost levels to match your new setup perfectly. This process ensures your engine runs not only powerfully but also safely and efficiently.

Skipping a professional tune is like buying a world-class orchestra and asking them to play without a conductor. The potential is there, but the result will be chaotic. Our expert engine tuning services bring your build to life, optimizing every new part to deliver smooth, reliable power and transforming your modified Subaru into the beast you envisioned.

How to Choose the Right FA20 Short Block

Choosing a built short block is one of the most significant upgrades you can make to your Subaru. It’s the foundation of your entire build, so getting it right is crucial. The perfect choice comes down to understanding your own needs and knowing what to look for in a quality engine builder. Let's walk through the two most important factors to consider so you can make a confident decision.

Define Your Performance Goals and Driving Style

First things first: What are you building this car for? Before you even look at a single part, you need to be honest with yourself about your performance goals and how you plan to drive. Are you aiming for a reliable daily driver with some extra punch for spirited weekend drives? Or are you building a dedicated track monster designed to chase lap times? Your answer completely changes which short block is right for you.

The biggest factor driving the cost and complexity of a built short block is its power rating. An engine built to handle 800 horsepower requires different components and clearances than one designed for a more modest 450 horsepower. Defining your target power level upfront ensures you invest in a block that meets your needs without overspending on capabilities you’ll never use. Thinking this through will help you find the perfect balance of power, reliability, and budget for your Subaru WRX upgrades.

Consider Brand Reputation and Warranty

Once you know what you need, the next step is deciding who to trust to build it. The quality of a short block comes down to the builder's experience, the materials they use, and the precision of their assembly. Look for companies with a long, proven history in the Subaru community. A strong reputation is built on years of successful builds and happy customers. High-quality builds use premium components like forged pistons and connecting rods, which are essential for handling the increased heat and stress of a high-performance application.

A solid warranty is another clear sign of a reputable builder. It shows they stand behind their craftsmanship. For example, we offer a 12-month/12,000-mile warranty on our engines because we're confident in our work. Also, be aware of core charges. Many builders require a deposit (the core charge) that you get back after sending them your old engine block. This is a standard industry practice, but it's good to factor into your initial budget. Ultimately, choosing a trusted builder for your performance parts is just as important as the parts themselves.

Installation and Break-in: Getting it Right

You’ve chosen your FA20 short block and are ready for the next step. But the journey to reliable power doesn’t end with the purchase. Proper installation and a meticulous break-in period are absolutely essential to protect your investment and ensure your new engine delivers the performance and durability you expect. Getting these two steps right will set the foundation for thousands of miles of enjoyment, whether you’re on the street, track, or trail. Think of it as the final, critical phase of the build itself. Let’s walk through what you need to know to do it correctly.

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

Deciding who will install your new short block is a major decision. Let's be honest: pulling an engine apart can feel like a monumental task, and the idea of tackling it yourself can be intimidating. However, with the right tools, a clean space, and solid guidance, many enthusiasts successfully complete the job. The DIY route can be incredibly rewarding and save you money on labor.

On the other hand, a professional installation by a reputable Subaru specialist offers peace of mind. These experts have the experience to handle any surprises and ensure every component is torqued to spec. Entrusting your build to a pro who provides engine tuning services also means you get an expert eye on the entire setup, which can prevent costly mistakes. Ultimately, the choice depends on your mechanical skill, confidence, and budget.

The Break-in Process for Maximum Engine Life

A built engine needs more care than a stock one, and the break-in period is non-negotiable. The first 1,000 miles are the most important for your engine's long-term health as the piston rings seat properly against the cylinder walls. To do this, drive gently with varied speeds and RPMs—avoiding both high-revving and lugging the engine is key. Constant highway speeds are not your friend here.

Plan for an early oil and filter change at around 500 miles to flush out any assembly lubricants and initial wear particles. After the break-in is complete, you’ll need to adopt a more frequent oil change schedule, typically every 3,000 miles. It’s also smart to actively monitor your engine’s health with gauges. Following these steps ensures all the new performance parts settle in correctly for a long and powerful life.

Protect Your Investment: Long-Term Maintenance

You’ve invested in a high-performance FA20 short block, and now it’s time to protect that investment. A built engine is a different beast than a stock one, and it requires a more attentive maintenance routine to match. Think of it less as a chore and more as the final, crucial step in your build. Proper long-term care is what separates a reliable, high-power machine from a costly headache. By adopting a few key habits, you ensure your engine delivers the thrilling performance you paid for, mile after mile. This isn’t about just following the factory service manual anymore; it’s about creating a new standard of care for your upgraded Subaru.

Your New Maintenance Checklist

To keep your built FA20 running strong, your old maintenance schedule needs an upgrade. A modified engine operates under greater stress, so it needs more frequent attention. Start with these non-negotiable habits:

1. Change Your Oil Frequently: Plan on changing your oil and filter every 3,000 to 4,000 miles with a high-quality synthetic oil. This is the single most important thing you can do for engine health.
2. Monitor Vitals: Install gauges for oil pressure and temperature. These are your engine’s vital signs, giving you a real-time look at its health and allowing you to catch potential issues before they become serious problems.
3. Get a Professional Tune: Any time you add new performance parts, a professional tune is mandatory. Proper engine tuning services ensure all your components work together harmoniously, optimizing performance and preventing catastrophic damage.

Key Practices for Engine Longevity

Beyond the regular checklist, a few key practices will maximize the lifespan of your FA20 short block. If you have a freshly built engine, following a strict break-in period is critical. This process allows the new components, like piston rings and bearings, to seat properly, which is foundational for long-term reliability.

Always use high-quality oil and coolant, as cheap fluids can compromise performance and accelerate wear. Finally, make regular inspections a habit. Proactively check components like the PCV valve and ensure your Air Oil Separator (AOS) is functioning correctly to prevent oil contamination and pressure issues. An AOS is one of the most effective performance parts you can install to safeguard your engine’s internals. These practices will help you enjoy your build for years to come.

Related Articles

• FA20 Long Block: Everything You Need to Know
• Built FA20 Engine: Everything You Need to Know

Frequently Asked Questions

Do I really need a built short block for just a few bolt-on mods? For basic modifications like a cat-back exhaust or an intake, your stock FA20 engine is perfectly fine. The real question to ask is what your long-term goals are. If you plan to add a larger turbo or push for power levels beyond 350 horsepower, you are entering the territory where the stock internals become a liability. Upgrading to a built short block is about creating a reliable foundation that can safely support the power you want to make, both now and in the future.

Is a built engine less reliable for daily driving than a stock one? This is a common myth, but the opposite is actually true. A professionally assembled built engine is engineered with components that are far stronger than the factory parts they replace. When paired with the right supporting modifications and a proper professional tune, a built engine is significantly more durable and can handle the stress of daily driving at higher power levels with greater reliability than a stock engine pushed to its absolute limit.

Can I reuse my stock cylinder heads with a new built short block? Yes, absolutely. Using your factory cylinder heads on a built short block is a very common and effective strategy, especially for street-focused builds. The short block provides the strong foundation needed to handle more power, and your stock heads are perfectly capable of supporting significant performance gains. This approach allows you to invest in the most critical part of the engine first and gives you the option to upgrade the heads later if your power goals increase.

What's the most common mistake people make after installing a built short block? The biggest mistake is failing to treat the engine as a complete system. Many people invest in a strong short block but then neglect the supporting modifications or skip a professional tune. A built engine requires more fuel and creates more heat, so an upgraded fuel system and cooling system are essential. The final, non-negotiable step is a professional tune, which ensures all the new components work together safely and effectively.

Why is the break-in period so critical for a built engine? The first 1,000 miles are crucial because this is when the new piston rings wear into the cylinder walls to create a perfect seal. A proper break-in, with varied RPMs and no heavy loads, ensures maximum compression and minimal oil consumption for the life of the engine. Rushing this process or skipping it altogether can lead to permanent damage and prevent your new engine from ever reaching its full performance and reliability potential.