Tearing Down and Assessing the FA20 & 4U-GSE

Article by Brian Hannon. Photography by Nathan Leach-Proffer and Ryan Randels.

Every week this build gets more and more interesting as we dive deeper into the inner workings o the Subaru BRZ and Scion FR-S platform. Last week we took a look at the first step in our build process: reinforcing the chassis by seam welding the structural body components. For this installment, we peel back the layers of the engine to understand what we have to work with, and where it can be improved in relation to our initial build objectives. As with any good build, you define an objective based on what you have to work with. In order to properly understand what we had to work with first hand, it was necessary that we dive into the platform’s heart. This time, we turned to SCR Performance because of their intimate knowledge of Subaru drivetrains, as well as their reputation as top engine builders. We knew they would give an accurate assessment of what areas we’d need to address as the build progresses.

While Project BRZ was off getting work done on various other components (seam welding, suspension assessment, etc.), our donor engine arrived at SCR for teardown and assessment. SCR requested we source a used engine so they could properly analyze and assess the stock platform’s weaknesses and wear points. We liked this idea, as a used engine would show any potential weak points since it has been exposed to the wear and tear of every day abuse, and can tell expert builders what they need to look out for when adding more power.

Once the donor engine, with 18,000 miles on the clock, arrived, SCR immediately started tearing it down and documenting what they found. All of the information provided in this article came from SCR’s direct assessment, as well as several conversations with other key industry personalities. We’ve broken down the assessments into the following major component groups: bottom end, top end, fuel, ignition, oil and cooling.

FA20 / 4U-GSE Engine Specs

Before we tear it apart, let’s have a quick refresher on the stock motor we’re dealing with.

• Engine Code: Subaru – FA20/Toyota – 4U-GSE
• Developed from the FB engine (Subaru Forrester)
• Developed with goals of weight reduction, while maintaining durability
• Horizontally opposed (boxer) 4-cylinder dual overhead cam engine
• 1998cc, square 86mm bore and 86mm stroke
• Toyota’s D4-S injection system (port and direct injection)
• AVCS (Active Valve Control System)
• Compression Ratio: 12.5:1—very high value rarely found on production engines
• Redline - 7,450 rpm
• Power Output – 197hp @ 7,000 rpm, 151 lb-ft @ 6,400 rpm

Subaru did an impressive job of cramming a lot of technology and capability into a potent little package. This gives us a lot to work with as we get ready to wring out a lot more power from our FA20!

Initial Teardown

As SCR tore down the engine, they gave us their thoughts on what they found. Though it did have just 18,000 miles, there was no sign of excessive wear on bearings, sides of the pistons, cylinder bores and crank journals. Not too surprising, but if any areas of concern were rearing their heads that would be a focal point for us to address during the build.

FA20 / 4U-GSE Bottom End and Rotating Assembly

The heart of the powerplant is the block, which is unique to the FA/FB series of engines, and features an open deck design. On other motors, they will cast the block out of solid billet or similar material and then drill out the ports and passageways into it, forming what is called a "closed deck.” On the FA, they cast all these voids in for the oil and coolant as it’s a more cost-effective process, and keeps the weight down, though the tradeoff is reduced cylinder pressure support you would require for high-performance applications. When the air fuel mixture ignites, you have a huge pressure spike in the cylinder and combustion chamber, and the forces are pushing at all angles. Something is going to give eventually if enough pressure is applied. Since we plan to add forced induction, you can certainly understand why this is an area of concern for us.

Fortunately, there are some options available. Though this is a bit low-tech, some drag race motors have the coolant passages filled with concrete to make a solid block. This adds strength to the cylinder walls, but obviously isn’t realistic for a performance application that runs further than a quarter mile at a time. We aren’t doing that. The other, more refined and accepted option is to employ sleeve inserts. The stock FA20 has thin iron liners that act as a friction surface (similar to a bearing) to keep the piston rings from wearing directly on the aluminum cylinder walls.

For our build, SCR doesn’t feel it’s necessary to re-sleeve the block based on the objectives we developed. They are basing that assessment on what others builders have accomplished so far. Case in point, Full Blown is already claiming 700hp on the stock bottom end. Not too shabby.

These motors seem to be making serious power, but the longevity is what’s in question. What’s the failure point? What’s going to eventually fail at those bigger power levels? We are still waiting to see as there are several companies pushing the envelope. Fortunately, the FA20 is proving to be pretty strong, even when laying down some pretty big power numbers.

SCR didn’t find too many surprises with the crankshaft, but did find one item of note. Compared with the EJ-series cranks, the FA has thinner rod and main bearings because the engine wasn’t designed to produce the power levels of the EJ. The engine was designed to be high-revving and efficient, which the thinner bearings help with. Keep in mind that, anytime you reduce friction surface area, you reduce drag, leading to more efficiency of the rotating assembly.

Subaru has done a good job of producing a very high-quality bearing used on the crankshaft and rods. SCR doesn’t see any reason to put a different bearing material or change the tolerances.

The rods have a fairly unique feature found in boxer-style engines. While most rod caps are cut at a straight angle, the FA20’s rod caps are angled, which allows you to remove the rods and pistons without splitting the case halvesvery handy for limiting time during maintenance and upgrades.

Another key point is that Subaru cast the rod as a full assembly, scored the rod, then used an impact to break apart the cap from the rest of the rod (this maintains the natural grain of the metal, stronger design). This process not only yields a stronger design, but also reduces production cost; best of both worlds for the manufacturer. Be sure that you don’t mix the rods and caps up in any way when reassembling the bottom end as they fit together like a puzzle!

The piston ring gaps are pretty small at the top and the lower ring gap is quite a bit wider than what SCR is used to seeing (compared to the EJ-series). The thought is the small gap up top prevents compression loss and the larger gap at the bottom allows for gasses to escape into the crankcase, and not build up between the rings.

When it comes to the pistons, we’re actually going to rely on our partners at Crawford to help us out with that information. They’ve already done the R&D and have designed a custom set of pistons that are different than all the other off-the-shelf products. They’ve gone above and beyond to redesign the part, having changed pin locations and rod lengths to get better rod ratios, and reduce piston side loading on cylinder walls to help the engine work more efficiently and rev up quicker to perform the way they want it to. It’s important that we address the ring gaps specifically for our application, as it will certainly change due to the fact that the engine will now be turbocharged.

One thing SCR noticed during disassembly was the excessive use of sealant–Subaru used an absolute ton of it. While Subaru did their best to make sure the engine wasn’t going to leak any oil, it certainly made it difficult to disassemble. SCR had to cut the sealant, working all the way around the perimeter of the part just to separate it. This proved VERY time intensive to separate and clean the components of all the sealant.

SCR speculated Subaru didn’t want to use a composite gasket as it becomes a failure point. Subaru has a fairly good track record to support their decision, though, as all EJ-series Subaru motors have sealant in between the block halves, and you hardly ever hear about leaking there. It’s basically two machined surfaces with sealant: so there’s no way it can develop a leak unless there’s been excessive force or improperly applied.

FA20 / 4U-GSE Top End and Valvetrain

As SCR learned, cylinder head removal has a few extra steps with the FA20. To get the cylinder heads off the engine, you actually have to pull the cam bridges off since they block all access to the head bolts. Common sense will tell you that you can’t physically remove the head until you have access to the bolts. There is some silver lining, though, as the cam bridges are actually a modular setup that keeps the cams in their cam bearing journals when you remove the bridges.

Subaru has transitioned to a roller rocker-style, cam lifter design, which helps reduce a friction point in the valve train. Since it’s still a solid lifter design, it’s something that, over time, will need adjustment to keep within spec. Unfortunately, the cam bridges rear their ugly heads again as you have to remove them if you want to adjust the valve clearances.

The intake ports look generally large when compared to the normal EJ-series, but we won’t know for sure until we run the heads on a flow bench to obtain the necessary data. As we mentioned in a previous article, the factory intake manifold no longer has a pesky TGV like the old EJ-series and FB motors, since a premium was placed on smooth airflow to support the higher-revving nature of the FA20.

Continuing upstream, the high-pressure fuel injector is pretty similar in design to the rest of the industry, so nothing earth-shattering there. Between the multi-port and direct injection, they can get a better mixture of the fuel and air based on driving situations, giving more of a complete burn. Each of the different fuel systems has their own benefits and weaknesses allowing Subaru to exploit the best of both worlds. The direct-injection provides better fuel atomization under heavier loads, while the port injection helps to manage carbon build-up at lighter loads and idle.

Direct-injection systems require a high-pressure fuel feed (in the thousands of PSI), and generally you need mechanical assistance to elevate pressure to those levels. The FA20s pump is mechanically driven off the camshaft via three-lobes, so in one revolution it strokes the fuel pump three times. This takes fuel pressure from the electric in-tank pump from about 60 PSI to the needed thousands of PSI.

An oil-actuated system (ACVS for Active Control Valve System) allows for near continuous camshaft adjustment to offer the most power for a given throttle position and rpm. Both the intake and exhaust cams can alter their relation to the crankshaft, and the whole show is monitored by the ECU.

Speaking of the camshafts, SCR noted they have nice big fat lobes, so they may not be something we need to worry about swapping out. Couple that with the near infinite adjustability of the cam timing, and there may not be much need to put big aftermarket cam shafts in to get the power.

As SCR stepped into the combustion chamber, they noticed there is not a whole lot of clearance between the valves and the pistons. If you’re trying to go with cams that have higher lift and/or duration, you could potentially have interference issues.

The valve stems are pretty small on these motors to help out with air flow as the smaller diameter takes up less space in the intake and exhaust ports.

In the name of efficiency, lightweight valve springs are employed so the engine isn’t fighting against its own components to operate. However, because the springs are so light, they could have issues closing the intake valves when they are fighting against 30lbs of boost trying to cram into the combustion chamber. This is an area we are looking to address.

FA20 / 4U-GSE Ignition System

As with most newer performance vehicles, coil packs are used on each cylinder to control spark. This is a big advantage for tuning as ECU’s are so fast they can really utilize the independent coil packs, and direct injection, to essentially tune each cylinder independently.

Stock spark plugs are a heat-range 9, so they’re extremely cold plugs to begin with, and extremely detonation resistantsomething we’ll battle with forced induction.

If we have issues with blowing out the spark, we can always hook up an amplifier to boost the signal, but the kits are designed for a hot, heavy spark, so right now we don’t see the need to upgrade.

FA20 / 4U-GSE Oil & Cooling Systems

Since additional oil pressure is required for the variable cam timing system, the standard oil pump was designed with plenty of flow and is actually a fairly robust unit. We don’t see ourselves upgrading to a larger pump for our build.

FA20 / 4U-GSE Oil Pan

The FA utilizes an upper and lower oil pan where the upper is actually a functional component of the bottom of the block. On the EJ-series, it's not a two-part component. The "upper oil pan” completes the bottom part of the block, while the "lower oil pan” is generally small if looked at by itself. However, the upper oil pan will also contain a considerable amount of the oil capacity. The small lower oil pan also acts as a funnel since the pickup point is very precise. Encountering g-forces commonly found on race tracks will begin to cause issues with this design. A larger oil pan with baffling will allow you to not worry as much about waiting for the oil to drain from the heads while pulling some serious g’s.

If you are looking to turbocharge your FA20 like we are, you need to consider how you will get oil to the turbocharger. If you are working on a budget, you will need to add a port to the oil pan for a turbo oil drain line. Sounds easy, but placement can be very important (especially on a small volume pan like the FAs), and they can be more prone to leaks. It may be best to source an aftermarket pan that was designed specifically for turbocharged applications that have increased volume and careful consideration of return line placement.

Last but not least, SCR evaluated the radiator and associated cooling components. While the stock radiator seemed up to the task of keeping a stock, or mildly tuned engine, at a safe operating temperature, we’re ditching it in favor of one with more capacity. It may not necessarily need a larger unit, but with the power we expect the engine to make, along with mounting an intercooler in front of it, we want to ensure we won’t encounter any cooling problems whether we’re on the track or sitting in line to get into a show.

Fortunately, the rest of the cooling system was deemed OK as the water pump can flow plenty of fluid, and the stock heat-range thermostat will most likely be fine. There are companies that can provide a lower-temp thermostat, but typically you want to have the engine running at the right temp as it will help with proper atomization of the fuel.

That surely was a mouthful, but we feel this was one of the most important articles in our entire BRZ / FR-S Performance series. Now that we understand the strengths and weaknesses of the platform’s powerplant, we can start to address those items with upgrades. Next week we're postponing our documentary article to the following week as the team will be in Houston for TX2K14. In that installation, we will take a look at our new Air Lift Performance suspension with an overview, unpacking, and analysis (visual inspection and comparison)! Since we got our hands on it, and are able to measure clearances and adjustability, we’ve developed a specific build plan that we know you’re going to love!

The Subaru BRZ / Scion FR-S Platform Series Partners

Please take a moment to check out our partners, whom without, none of this would be possible:

Heuberger Motors
The world's most enthusiast-friendly Subaru dealership.

SCR Performance
The Performance Expertise Behind the BRZ / FRS Platform Series.
Visit them on the web @

SLVA Automotive Studio
Where Form meets Function.

Our Audio and Aesthetics Partner aka the Architects of Fidelity.
Visit them on the web @

AR Design
The Fabrication Masterminds Behind our Forced Induction Systems
Visit them on the web @
Our Sport-Compact Performance Parts Source. . . Never Compromising Quality or Customer Service.
Visit them on the web @
Visit them on Facebook @

Air Lift Performance
The Progressive Behind the Build
Visit them on the web @

Maintaining Integrity & Strength through CUSCU Performance
Visit them on web @
Visit them on Facebook @

Wilwood Engineering
The Stopping Power
Visit them on the web @

Advan Racing
Bringing Together Performance & Aesthetics
Visit them on the web @

Turbo By Garrett
Forced Induction at its Finest
Visit them on Facebook @

Yokohama Tire Company
Power is Nothing without adequate Traction.
Visit them on the web @


Bhrp's Profile Image

Brian Hannon (BHRP)

Grew up around cars and racing, a passion fueled by my whole family. Participated in numerous track days with cars and motorcycles as well as covered the NASA East Coast Honda Challenge for Grassroots Motorsports. Now that I'm in Colorado I'm enamored with the Pikes Peak International Hill Climb... borderline obsessive...
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Write a CommentCOMMENTS
heathercarterabout a month ago

Great windshield replacement company.

Matthew Dylla8/13/2019

So I'm planning on getting a 2017 86, have they changed anything that wasn't outlined here? I don't know if I'll go the turbo route but I do want somewhere around 240-280 HP to deal with the inclines where I live in Utah so I really love the information you guys have here. I'm tracking on the rods, return springs, and possibly the fuel pump and cooling system so far. If I missed anything please let me know while I try and catch up to 2019, but already really impressed with what was to my understanding a sort of begrudgingly co-op engine and car.


How did I never know about this website?!?! WOW, amazing photos and very in-depth technical approach. *Saved*


Do you know what the stock rod/stroke ratio is? And with Crawfords adjustments?


did you get a weight for the engine?

Bhrp's Profile Image

We did not get a weight for the engine... assume you're looking for stock?

Drxlcarfreak's Profile Image

Nice write up! Can wait to see the build up.