Subaru Wrx Sti Engine Diagram

You'll notice in the title of this blog, we say everything you need to know; versus what we want you to hear, or what our opinion is. Here at Crawford you will only ever hear proven facts, and the information that will allow you to make your own educated decision on what you do under your hood.

First we'll get in to the terms (in bold) and their meanings and how they relate to the products you are buying, so as you read this article or any others on the inter-webs, you'll have a much better grasp on what you're looking at.

Engine Part Sources

If your car came new from the dealership, then it 100% stock or OEM (Original Equipment Manufacturer). These terms describe the parts that were installed on/in your car from the factory. If something is aftermarket, then it has been manufactured or modified by a factory or shop other than Subaru.

Genuine OEM Subaru parts are truly high quality parts. Many decades of research, development, investment, trial and error have gone into these parts; far more than 90% of any aftermarket manufacturers. Yes, they are expensive. But think to yourself for a moment why aftermarket parts are cheaper. QUALITY. OEM parts are quality parts that are proven. Most knock-off parts are manufactured in China, with sub-par materials in dirty factories. You get what you pay for in the automotive industry, so bargain shopping will not keep your Subaru reliable. Be sure to do your research on companies and their components, and be ready to invest in your car if you want to do it right, and do it once.

Types of Subaru Engines

The first Subaru Engine used in the US is the E series. Most Subarus you see on the road today have an EJ, and in 2011, Subaru introduced a completely redesigned engine, the F series. FA and FB engines are beginning to replace all EJ engines, with only the EJ257 still in the STI as of 2019.

A quick list of popular US models and the engines they run:

EJ20

2002-2005 Subaru WRX

EJ25

2006-2014 Subaru WRX
2004-Present Subaru STI
98-2011 Impreza
1996-2010 Legacy
1996-2012 Legacy GT
1996-2012 Outback
1998-2010 Forester
1998-2013 Forester XT

FA20

2013-Present BRZ/FR-S/GT86/86

FA20 DIT

2015-Present WRX
2014-2018 Forester XT

FB20

2012-Present Impreza
2013-Present XV Crosstrek

FB25

2011-Present Forester
2012-Present Legacy
2012-Present Outback

If you'd like to see the full history and lineup of Subaru engines, this Wikipedia article has it all: https://en.wikipedia.org/wiki/Subaru_EJ_engine

Most of the aftermarket power and engine components you will find are for turbocharged Subaru models. This is due to the fact that until 2013, no NA (Naturally Aspirated / Non-Turbo) models were tuneable. That means you couldn't adjust the car's computer, or ECU, to accommodate for the changes made under the hood past an intake or headers. There is also no need to build the engine if you're not making big power. There are ways around this, but they usually come at a heavy cost and require completely re-wiring your engine and making it no longer road legal. Swaps are popular with NA models for this reason, but take a phenomenal amount time and money.

Parts of your Engine

The complete engine is what comes out of your engine bay in its entirety. It is everything, minus the intercooler, piping, hoses, and fluid reservoirs. Also known as Turn-Key.
Complete Subaru Engine

A complete long block strips away bolt-on components such as your turbo, manifold, and headers.

Complete Subaru Long Block

A bare long block is the same thing, minus the valve covers, timing components, cams, and pulleys.

Subaru Bare Long Block

The short block is the center of the engine, with the cylinder heads removed. It includes its internals: the pistons, rods, crank, bearings, and rings.

Subaru Short Block

Cylinder heads are bolted up to each end of the short block.
Subaru Cylinder Heads

Inside the short block, you will find the moving parts that make your engine purr. These are known as internals.

At the very heart of the short block is your crankshaft (crank), which turns the crank pulley on the back of your engine. This rotating motion is translated to your drivetrain which turns your wheels.
Subaru crankshaft Connected to your crank are your rods, with the appropriate official name of Connecting Rod. It connects the crank to the piston, which is forced to move in and out of the cylinders by internal combustion (explosions). RPM's are how many times per minute an explosion happens between all cylinders in your engine. When an explosion happens, the top of the piston gets the direct impact, and the rod has to be even stronger due to its length and direct connection to the piston via a wrist pin.

The piston rings are placed into grooves on the top edge of the pistons, and they close the small gap between the piston and the cylinder wall in order to hold back exhaust from entering your crankcase. Some still slips by through the ring gap, and this is know as blow-by.
subaru pistons
Subaru piston parts You may have heard the myth:

"EJ engines are just plain prone to ringland failure."

This is when the spaces in between the ring gab break. This is mostly false. This myth is used to sell aftermarket internals and aftermarket tunes that boast the claim of reducing your chances of this happening. In a way, the myth is true, but not for the simple reason of the structural design or factory tune. This statement is only true if you do not take care of your engine, i.e. letting the oil run low, not changing the oil enough, modding your car without a proper tune, using the wrong fuel, etc. Broken ringlands and bearing failure come from detonation and oiling issues, which can be avoided with an Air/Oil Separator, a solid tune, and proper maintenance. Learn more about our recipe for a healthy engine in the section titled: 'What do I need to keep my Subaru Engine Reliable?'.

In relation to short blocks, you may have heard the terms Closed Deck Block, Semi-Closed Deck Block, and Open Deck Block. Decks are the space between a cylinder wall and the crankcase, where coolant flows through to keep the cylinder walls cool. (show picture with deck circled, with cylinder wall and block labeled). The cylinders encase the pistons, where internal combustion occurs, therefore this is the part of the engine that receives the most abuse. The cylinder walls are exposed to explosions with high heat and impact, and expand and contract when the engine is on and off. Therefore, this can be the weakest link in a block besides its internals if it does not have enough structural support and thickness.
After 2005, all Subaru engines are Semi-Closed Deck. They have a few points of reinforcement to increase the strength of the cylinder wall. Open decks can be seen in early non-turbo engines, and the first 2 generations of WRX's. These are the weakest Subaru engines, due to the fact they have next to no cylinder wall reinforcement.
Subaru short block parts Closed Deck was once used long ago (early 90's) by Subaru but quickly discontinued due to its lack of reliability. Today the concept is entirely aftermarket, where the coolant passageways of semi-closed and open deck blocks are filled with metal making a solid connection between the cylinder wall and crankcase. Sure, it's strong as hell, which is why it was first practiced in the racing world with extreme heat and high horsepower builds. It kept the cylinder walls in one piece for a longer period of time, extending the amount of race miles each engine lasted. The downside to the added strength is the fact that the coolant passageways are sealed off, causing the engine to run at higher temperatures and frequently overheat. This makes the internals fail quicker, despite the block itself staying intact. There are other ways to cool an engine with aftermarket modifications, but they cost and take away cohesion in the engine bay. It's a cheap bandaid approach to those wanting to avoid a new engine. Shops that sell these blocks actually take old, retired blocks and repurpose them. This is why the cost is so low for people looking for a strong EJ engine, making them subsequently popular. They are also popular due to some misleading marketing; that the OEM semi-closed deck blocks are prone to failure and cannot support high power builds. This is absolutely not true if you maintain our recipe for a healthy engine in the section below.

What do I need to keep my Subaru Engine Reliable?

We use this term at Crawford quite a lot; a bit of a motto: "Don't fix what's not broken." This is what you need to keep in mind when modifying your Subaru with the intention of maintaining maximum reliability. We say maintaining, because there is no safer or more reliable build than keeping your Subaru 100% stock, minus of course premium fluids and staying on top of your maintenance schedule. That may contradict everything you've ever read about Subarus, but most of what you read is Joe Blow's opinion based on what? 9 times out of 10 it is a company trying to sell you something you don't need, hopping on the forums where rumors and insults spread like wildfire.

After 24 years of 100% focus on aftermarket Subaru research and development, our trial and error with their engines has given us the following recipe for an efficient and reliable Subaru engine:

1. Don't fix what's not broken.

We understand that a lot of you love your giant mod list. But if you want efficiency and reliability as the #1 component to your build, unless a part has proof that it offers the benefit advertised, don't modify a part that works just fine under your hood. OEM parts are meant to hold hands with one another, so when you start removing, adding, or modifying certain things, you will start to have one issue after another. We're sure you've heard the stories from many Subaru owners how their car's are a money pit and always failing.. well, most likely the have broken this first cardinal rule.

2. If you modify your car with power-increasing components, make sure to get a tune from a REPUTABLE and EXPERIENCED tuner.

This is arguably the MOST important factor in reliability. At any power level.. stock, bolt-ons, or race car. If you have a less than perfect tune, your engine will ultimately fail. This includes off-the-shelf or OTS maps. They are made for any car in the world; not taking into account the subtle differences from car to car, climate, altitude, fuel variations, etc. These should only be used to gingerly break in an engine, or drive gingerly from your shop to your tuner for a custom a tune. Never beat up your car on an OTS map.
Experienced tuner means someone that has been at it for a while; not someone who is practicing on your car. Ideally a tuner that has extensive experience with Subaru engines. Reputable means they have a good public track record.
If you're searching for a new local tuner, try attending local car meets and track events and just talk to people and hear what they have to say about their tuners, and how long their engine has been in one piece with power mods.
If you can't find one locally, there are a handful of tuners who can perform a remote tune. Again, find someone great and don't settle. This is the most important investment into your build.

3. Stay on top of maintenance.

This is as important as a solid tune. Subaru engines hate running low on oil. They are finicky. Unlike a Honda that can keep going on drops of oil like an anorexic chick on crumbs, running a Subaru engine low on oil alone can make your engine fail.
Volume is important, but so is the quality of oil you are using. For turbocharged Subaru Engines, definitely stick with a full synthetic unless you are breaking in a new engine. We have used and loved MOTUL for many years now. Oil is oil is oil, so as long as it's premium, you can't really go wrong. Also make sure you stay on top of changes. Only if using premium, you can go 4-5k miles keeping it topped off. Try changing the filter more often though; about every 2k miles. If your filter is on the bottom of the engine, this is difficult to do, but possible. You may lose a little oil in the process but as long as you're quick it can be done. Those of you with a filter on top have no excuse! Subarus filters are great quality, but we have always used and trust K&N completely.

4. Run a proper Air/Oil Separator (AOS)

We say proper, because there are many catch-cans on the market disguised or marketed as Air/Oil Separators. A good AOS can reduce detonation and oil consumption, while allowing your engine to operate at its full power potential. Being that Crawford designed and released the first Subaru AOS, and the fact that it is our #1 selling component, we have a lot to say on the subject. Click here to check out everything you need to know about Air/Oil Separators.

My engine failed. Now what?

The first step is to get to the bottom of why it occurred in the first place. Were you making too much power? Did you let the car run out of oil or neglect to change it for too long? Did you have a less than perfect tune and were experiencing detonation? Did you lose compression in a cylinder from ringland failure or broken rings (also form detonation)? Did you lose a bearing from a drop in oil pressure or detonation?

All of the above factors are typical causes of Subaru Engine failures. A compression and leak down test along with studying your engine's history will help to get to the bottom of it. Once you have a reason, you can better choose the components and path to avoid it from happening again. It will set you back up to 10k depending on your engine of choice. Again, you get what you pay for, so make sure that the components and services you choose are premium unless you want to this all over again, and again.

Do I rebuild my existing engine or go new?

This depends on what type of engine you have.

If it is an EJ, you must choose new to avoid future failures. We know it's expensive, but here's why it's not a good idea to rebuild.

The weakest parts of the EJ engine are the cylinder walls. Being semi-closed deck, they don't have a lot of reinforcement. Especially if your engine failed from detonation, your cylinder walls are most likely out of round. This means that they are no longer perfectly round. Shops will measure the engine removed, and check for this. If it is in fact out of round, they will offer honing. Honing is the process of machining your cylinder walls back to perfectly round. They will hone each cylinder, then order oversized pistons that will fit the new dimension. The big problem with this is that you just took the weakest point in the engine, and made it thinner and subsequently weaker.

If you have an FA or FB engine, your cylinder walls are far stronger and usually don't go out of round at all. Rebuilding is definitely more of an option for these engines.

Either way, the most reliable path is a new block.

What about my heads?

9 times out of 10, Subaru cylinder heads are reusable following an engine failure. They are pretty bulletproof. The only exceptions to this rule are:

If you overheated the engine: this can warp and/or crack the cylinder heads.
You broke a valve or scored your cams. Sometimes you can just replace the cams or valves if they aren't too scored, but usually this means metal fragments from your engine have entered the cylinder heads and it becomes extremely difficult to clean these fragments out of all of the passageways. If any of these fragments end up in your new engine, you will have another immediate engine failure. Have your shop inspect your heads thoroughly to determine what if anything needs replaced.

If you are reusing your original heads, make sure they get resurfaced before being installed onto the short block. This ensures a like-new seal with your head gaskets and will avoid a future blown head gasket.

Should I take this opportunity to build my heads?

If you have a turbo, the short answer is no. In a turbocharged Subaru engine, the turbo does all the work. The amount of money it takes to build heads is not worth the insignificant gains you may receive, which can be easily achieved on the dyno by turning up the boost by 1lb. Aftermarket cams may give you a higher top-end power number, but you sacrifice power where you need and feel it in the low and mid ranges. These mods are better suited for an NA build.

With a new engine, what other parts need repaired/replaced with it?

Everything that oil touched needs thoroughly cleaned out to remove any metal fragments. These fragments can re-enter your new engine and cause it to fail again. The oil pump is impossible to clean thoroughly, so you will want to replace that new along with the oil pump main seal. Same goes for the oil cooler. In an FA or FB engine, the oil pump is built to the front cover on the engine, so you will need to replace that whole piece. If your engine has over 100k miles on it, you may want to consider a complete gasket kit that comes with every gasket in the engine. If lower miles, reusing a lot of the gaskets is perfectly fine. That being said, the gaskets that should be replaced no matter what are the intake, exhaust, water pump, and head gaskets. Make sure your new short block goes together with 11mm ARP head studs. These are reusable indefinitely, and are 1000x better than the OEM head studs. Fun fact; they were originally designed by Quirt Crawford. You will also want new spark plugs and we recommend using this opportunity to upgrade those as well. We recommend NGK one step colder Iridium plugs. And lastly, of course, new break-in oil for your engine and a new oil filter.

All of the above mentioned components (minus the oil cooler because most people have aftermarket) come together to make up our Short Block Installation Kit. Click here to check it out.

At what power levels do I need to consider getting a built engine?

Believe it or not, if you follow our tips on how to maintain a reliable engine, an OEM EJ25 is capable of housing up to 400whp/480bhp! We have done it many times with our customer's builds. FA20 NA blocks can house up to 300whp/360bhp, and FA20 DIT blocks match the EJ25 at 400whp/480bhp.

If you have an FA20 NA engine (BRZ/FR-S/GT86/86), you can swap out your rods which are terrible and fail easy, to the FA20 DIT rods that come in the 2015 and newer WRX's. They are perfectly compatible, and much stronger. This is a great compromise on your wallet when boosting your 86.

Built engine stages and their strength depend on the manufacturer. Ours are as follows:

S2: 450whp/540bhp
S3L-X: 550whp/660bhp
S3l-X with FSR Upgrade: 600+whp/720+BHP

Click here to check out our built blocks.

That's right folks: you don't need a closed-deck block for high HP builds!

What makes Crawford Built Blocks unique?

All components engineered and manufactured by Crawford Performance have been tested for ultimate performance and maximum dependability on and off the race track. For over 2 decades we have tested all combinations of upgrades for the turbo-charged EJ20, EJ25, and more recently the new FA20 Subaru engines. We have pushed these engines to their breaking points to determine which components fail at what level. From that research we have come up with forged internals to keep your engine strong enough to withstand your desired power level.

Our builds include the following upgrades over OEM:

S2

CrawfordSPEC S2 JE Forged Pistons. These Pistons are approved by the SCCA and stamped accordingly

S3L-X (formerly S3L-i)

CrawfordSPEC S3L JE Forged Pistons. These come with an option $250 upgrade for FSR, which is an even stronger billet forging. FSR stands for Forged Side Relief.
CrawfordSPEC X-Beam Pauter Billet Rods

About CrawfordSPEC Pistons

Every CrawfordSPEC piston features a unique dish design, engineered by and exclusive to Crawford Performance. Our lead engineer, Quirt Crawford, has worked side-by-side with JE Pistons to create a design with the following results:

More manifold vacuum at idle, which makes for a tighter, healthier, more efficient engine
Lower crankcase pressure
More power at same boost level with same supporting mods
All CrawfordSPEC pistons are sized for the OEM bore of 99.5.

About FSR Piston Upgrade

Piston forging developed by Quirt Crawford. Although the forging style is available to the public, our skirt length and dish design is exclusive to Crawford Performance. This forging upgrade features:

100% CNC machined from high quality 2618-T6 wrought aluminum bar stock
Specifically designed for high horsepower road and drag race engines
Internal and external bracing (bridge-like design) provides a more rigid construction while minimizing overall weight
Billet means pistons are machined on every surface allowing for all unnecessary weight to be removed during manufacturing, reducing excess friction/heat from high horsepower applications
Weight reduction of up to 32 grams
Includes high quality 9310 steel wrist pins
Reduced skirt width and shorter wrist pin when compared to traditional "full round" style forgings. The narrow skirt helps minimize piston contact with the cylinder wall that can cause friction and power loss while the shortened wrist pins reduces the overall weight.

About CrawfordSPEC Rods

Every CrawfordSPEC rod is designed at a specific length, engineered by and exclusive to Crawford Performance. Our lead engineer has worked side-by-side with Pauter Rods to create a design with the following results:

Longer than stock length not only increases strength but also increases the rod ratio which allows for smoother and more efficient power delivery
Billet vs. Forged, made with the strongest steel available in the industry: 4340 chrome-moly

Why doesn't Crawford use aftermarket cranks, bearings, rings, or gaskets?

It goes back to one of our motto's: Don't fix what's not broken. Our blocks are expensive due to all of the OEM parts that are included, which are premium. A lot of people are puzzled as to why our prices are higher than another companies blocks that include more upgrades. We'll say it again: you get what you pay for. Aftermarket parts are cheaper because they do not have the same quality standards as OEM. They are cheaper for a reason. And we do not and will not replace parts in an engine that do not fail. We have used and tested aftermarket cranks for example that are stronger than OEM. They have consistently had a higher failure rate than OEM cranks at the same power levels.

But I spun a bearing. The bearing must be the issue, right?

To answer this question, we must first explain how bearings work, so that why they fail makes more sense. This particular writeup on bearing failure was written by Quirt Crawford himself:

General engine bearing failure 101

FYI, this is a general letter to anyone that has had a bearing failure in their Subaru motor.

The Subaru motor has two sets of bearings in it, one set on the main journals of the crankshaft and another set on the rod journals of the crankshaft. The oil that lubricates and floats these bearings comes from the oil pump via the engine block and is fed into the crankshaft via the main bearings, so they see the oil first while the rod bearings see the oil secondly. With this fact in mind it is easy to diagnose if the rod bearing failure was caused by a lack of oil pressure, or from detonation / excessive loads.

If there is a lack of oil pressure then the main and rod bearings will be damaged from scoring with the rod bearings seeing the most damage as they see the highest loads. The damage to the bearings is usually even across all four rod and main journals, so you will not see just one bearing damaged from a lack of oil pressure.

Detonation / excessive loads on the rod bearings is very easy to diagnose as the rod bearings themselves are the only bearings that are damaged, leaving the main bearings fully intact. Detonation is like a giant hammer pounding on the top of the piston and this impact goes straight down the connecting rod and into the rod bearing which pushes out the very small film of oil keeping the rod bearing and rod journal on the crankshaft from making metal to metal contact with each other. Detonation can and will damage only one rod bearing at a time where a lack of oil pressure damages all four at the same time.

Statistics show that the large majority of Subaru motors that have damaged just one rod bearing happen to cylinder #3. There are many different opinions as to why this occurs and I will not go into this as it is not relevant to the topic of this letter.

When you have a bearing failure in your motor, cleaning out ALL of the bearing material inside your motors components as well as the turbo is of utmost importance! If this is not done correctly then your replacement motor and or turbo will fail from ingesting this leftover debris. Sadly this is also a high statistic in our industry… And the person that suffers from this costly mistake is always the vehicle owner as the shop that did the work usually does not even realize the mistake they made, so they blame it on something or somebody else. At Crawford we always throw away any and all oil coolers on the vehicle as getting the bearing debris out of them is impossible. The small filters in the cylinder heads must also be replaced, if not then the turbo will fail within 1000 miles of the new motor install. The oil pump will also be damaged from the bearing debris as will the oil pressure relief valve which is located in the body of the oil pump; at Crawford we never reuse the old oil pump either.

- Quirt Crawford, Founder of Crawford Performance

Have any further questions after reading this article? Feel free to reach out to us any time:

855-67-SUBIE (78243) Ext. 1
technical@crawfordperformance.com