#RevvProjectBRZ: Specifying, Designing and Fabricating the FA20 4U-GSE Turbo Kit

Article by Brian Hannon. Photography by Ryan Randels and Kenta Young.

Throughout the past few articles you’ve learned about the improvements we’ve made to the strength of the engine, and beefing up the fuel and cooling systems. This install we reveal why all of those modifications were necessary: forced induction.

One of the biggest let downs about the BRZ/FR-S was the lack of a turbocharged option. It seemed so simple, just pull the motor from the WRX and, voila, boost! Instead we were left with a car that, while well balanced, just wanted enthusiasts begging for more. Thankfully there is a healthy aftermarket that was practically frothing at the mouth at the opportunity to add forced induction.

First off, let’s introduce the group responsible for developing the forced induction solution for our FA20: ar design. They are one of the country's most revered automotive fabrication studios, and we are lucky to have them here in our backyard in Colorado. These TIG-welding specialists are primarily known for their top-notch BMW fabrication work as well as their attention to detail. Simple details like always using the best material solutions for the project and always back-purging to obtain full penetration welds, are the minor touches that set ar design apart in a major way.

They have a keen eye for the aesthetics, but are hell-bent on function and maximizing systems efficiency. Literally everything out of their shop is TIG-welded and back-purged to ensure a proper and strong full penetration weld.

Under the new ownership, they're moving into different platforms and working on expanding their existing platforms. Since they were known primarily as a downpipe company, they are working on moving into developing production turbo kits and larger scale one-off projects like our BRZ. With what we’ve seen with our BRZ, we have no doubt this move will be a success.

With the introductions out of the way, let’s get back to the BRZ and what ar design came up with. As you may recall from our initial goal for the build, we wanted to shoot for high numbers yet retain a reasonable and useable power band; this car would not be a dyno queen. Our FA20 will be pushed to the limit while being able to put the power to the ground throughout the power band.

Getting Boosted: Sizing the Turbocharger for our BRZ Build

Based on our build requirements, motor displacement and atmospheric conditions at altitude, SCR Performance developed flow calculations that led us to the turbo we had our hearts set on: the GTX series from Garrett. Part of that selection process would dictate the A/R exhaust housing size.

SCR knew that with a smaller A/R for the exhaust housing, we’d have a quicker spool but could potentially compromise the top-end power. The trade-off is either choking the motor out or having it so wide open that it can't spool. In the end SCR recommended a 1.01 A/R housing.

Now it was time to source the turbocharger package. After scouring Garrett’s catalog and consulting with their engineers, we landed on the externally gated, twin-scroll Garrett GTX3076R to match all of our performance specs.

Let’s break down the turbo to see what we got our hands on. The GTX3076R was designed for motors from 1.8 to 3.0 liters with expected power outputs from 360-640 hp. It features a forged, fully machined compressor wheel and dual ball bearings with housing that is both oil- and water-cooled. On the compressor side we have a 58-trim billet compressor with a 58-mm inducer and a 60-mm turbine wheel. The compressor housing also has a 4-inch ported anti-surge shroud with a 2-inch discharge. Helping to spin up the compressor is a 76-mm exducer on the exhaust side.

Our own Josh Luckabaugh provided us some great guidance on how to pick your turbo size:

"Although today there are a plethora of options from factory equipped turbo car manufacturers such as Holset, Mitsubishi, Borg-Warner, etc., to aftermarket manufacturers marketed solely for the performance market such as Garrett or Precision, turbo selection can be quickly narrowed down by looking at a turbo’s compressor map. Using the ideal gas law equation, your engine size and approximate power output (or boost level), you can plot on a compressor map where the turbo will be for your engine to make sure it is a good fit. Proper sizing is a crucial part of turbo selection. A turbo that is sized too large for your application, will give you increased lag and suffer a loss in low end torque; too small and you will lose out on top end power. Once you know the general size of the turbo, you can look into options such as direct bolt-on turbos (in the case of upgrading a car that is already turbocharged), anti-surge housings, ball bearing or journal bearing turbos, billet compressor wheels, divided or undivided turbine housings, etc. The list goes on and on. Each of these options could have their own write up on how they work and the advantages and drawbacks of each, but the general principle behind each is to either help drivability, increase boost response or make the turbo act like a larger turbo.”

In order to reduce the spool/lag of the 2-liter boxer with our build goals, we were OK with potentially compromising the top-end power and going with a true divided/twin-scroll application. Why twin-scroll? Properly matched twin-scroll systems (manifold and turbo exhaust housing) deliver superior airflow compared to single-scroll or OE-twin-scroll designs. According to, twin-scroll turbo kits have higher back-pressure at low rpm (good for turbo spool-up) and lower back-pressure at high rpm (good for top-end performance). This sounds like exactly what we’re looking for.

Now that we had the turbo spec’d and sourced, it was time for ar design to work their magic with the metal. Design considerations were aimed at being able to fit the entire turbo kit and supporting elements into the compact, yet welcoming, available space. Special focus was applied to optimizing exhaust and intake airflow, reducing inefficiencies such as obstructions, and fitting the required components while maintaining proper radius bends and strong flow is always a challenge. We want to make sure we’re taking full advantage of the increased turbo efficiency found in the twin-scroll setup.

Designing and Buiding the BRZ/FR-S Exhaust Manifold

Harnessing the energy created by the engine is an exercise in maximizing efficiency to obtain the greatest results. At peak horsepower levels, you want to make sure you can minimize the obstructions on both the intake and exhaust side. Unfortunately, while twin-scroll provides great spool characteristics, it is considered an obstruction and could potentially jeopardize our top-end power. Given our objectives, this is a compromise we're willing to make to maintain drivability. What that compromise means in terms of specific numbers, we will have to wait and see.

Based on guidance from the engineers at Garrett, we employed the following recommendations into the design of our system:
· Make the exhaust primaries equal length to balance exhaust reversion across all cylinders.
· Maximize the radius of the bends that make up the exhaust primaries to maintain pulse energy.
· Avoid rapid area changes to maintain pulse energy to the turbine.
· At the collector, introduce flow from all runners at a narrow angle to minimize "turning" of the flow in the collector.
· For better boost response, minimize the exhaust ports and the turbine inlets.
· Divide/separate the cylinders whose cycles interfere with one another to best utilize the engine's exhaust pulse energy.
· The proper grouping for an engine is to keep complementary cylinders grouped together. Because of the better utilization of the exhaust pulse energy, the turbine's performance is improved and boost increases more quickly.

    With the twin-scroll housing on the GTX, we wanted to make sure we produced equal-length primaries off of the boxer engine to properly scavenge the exhaust pulses to help spool the turbo.

    With divided headers, we were also required to run two wastegates of the Tial MV-S v-band variety, instead of just one. This increased cost and weight of the overall system, but does provide an increased safety margin with regard to boost control. We could have collected the exhaust prior to the turbo and run a single wastegate, but having the new Garrett divided exhaust housing allowed us to keep the exhaust pulses separated until it hit the turbine, maximizing efficiency, a trade-off we were willing to make.

    Since the fabrication was already becoming unique to our build, we also wanted to integrate some little touches to set it apart from the off-the-shelf kits.

    One of those small details was, instead of squaring up the turbo in the engine bay, we have it sitting slightly cocked. This allows for a more direct access to the cold-air intake routing. Less bends, better flow. More power.

    As we mentioned in a previous article, our upgraded oil pan with increased capacity posed an additional problem as it's deeper than stock, requiring some ingenuity with the plumbing of the pipes under the motor. The resulting fitment issue required additional design work to make sure the now longer primaries were still of equal length.

    Designing and Fabricating the Turbocharged FA20 Cold Air Intake

    In order to prevent from drawing the hot air from inside the engine bay, we wanted to pull cool air from in front of the wheel well. The pie-cut aluminum tubing is for both aesthetics and performance, minimizing obstructions and reducing mandrel bends.

    Designing and Fabricating the Turbocharged FA20 Hot-side Piping

    Now that we’ve got the air in we want to keep it nice and cool to keep the engine happy. The starting point is the routing to the intercooler where we look to dissipate as much heat as possible before mixing the air with the fuel.

    As the compressed air exits the turbo, it is routed out the front cowl to reduce unnecessary piping to the maximum extent while minimizing bends to maximize velocity out of charged air.

    As with most of the build, we went with a custom front-mount intercooler. We sourced an intercooler core from Garrett/Honeywell that meshed with our power requirements and, in the interest of time, we sourced two cast end tanks and welded them onto the aluminum core.

    In typical BRZ/FRS turbo kits, the intercooler has top-mount exits. Due to size [width] of our intercooler setup, we couldn't use this type of exit as it would require heavy modifications to the headlight assemblies. Instead, we modified the end tank, plugged the cold-side and made our own exit that ran laterally out the side. This minimized chassis and component modifications and provided a clear shot under the headlight and up into the engine bay.

    Cold-side Piping

    From that side exit of the intercooler, we were required to make the cold-side piping slightly longer than other kits on the market.

    The piping travels from the intercooler, under the headlight and back into the engine back where it meets up with the intake manifold. Though the piping may be a little longer than we like, it does help keep the charge isolated from the hot engine bay just that little bit longer, hopefully not absorbing unnecessary heat.

    Designing and Fabricating the Turbocharged FA20 Downpipe and Exhaust

    It’s a shame most of the downpipe resides under the car and out of sight as you miss a lot of the amazing craftsmanship from ar design.

    The 3-inch 304 stainless piping from turbo to exhaust tip was 100 percent TIG welded, back-purged with full penetration welds.

    The design of the downpipe was fairly basic as it exits the exhaust side of the turbo and turns down, literally the quickest escape for the exhaust gasses.

    Because of the close proximity of the intake piping, it was necessary that we not only ceramic coated the down pipe, but also wrapped it in heat wrap. This helped to improve thermal performance and to keep the heat away from the intake and reduce overall engine bay temps. We also thermal coated the exhaust headers and primaries and the exhaust manifold for a nice touch.

    From there it’s a full custom exhaust with a single in-line resonator to really hear the 'charged FA20 breath. The system finally terminates with a trick single-exit segmented turned up tip to really set it off from the other aftermarket options.

    Full #RevvProjectBRZ Turbo Kit by ar design

    We’re getting closer and closer to the conclusion of the build, but we still have some major items to cover. Suspension, interior, stereo, tuning, wheels and tires. OK, maybe we still have quite a ways to go and we still need to rip this car around the track! Big thanks to ar design for all of their skill and craftsmanship in bringing together our one-of-a-kind turbo solution. Keep checking in on Revvolution as we bring you updates on one of the best BRZ builds to date!

    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 @

    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 @


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    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...
    Brian Hannon on Google+

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    Rockysds's Profile Image

    Not yet Theo! Soon... Such great work by Jon Vigil and the ar design team


    The build is looking fantastic! Have you guys posted a video anywhere so we can hear the sound?