General tuning guide
2013 Scion FR-S and Subaru BRZ performance and tuning guide
The 2013 Scion FR-S and Subaru BRZ vehicles are the two most iconic modern JDM tuner vehicles thanks to a rich motorsports heritage. Built on the ideals of previous vehicles such as Toyota 2000GT and Sprinter Trueno AE86, both the FR-S and BRZ are twin vehicles with only minor tweaks to suit the ideals of each enthusiast group. They are designed from the ground up to be modified and built to each owner's liking. If you are looking to get the most performance out of your FR-S or BRZ, you have come to the right place.
Disclaimer: The following guide is a written theory based on a combination of performance and engineering theory. It is not definitive and when you modify a vehicle there are many other factors that come into play to determine the overall outcome. If you start modifying an engine for additional performance, anything can happen if you don't do it perfect. That can't be stressed enough. You must have a good understanding of how modern electronic fuel injection functions and interacts with ECU programming or you will blow up your motor. Proceed with caution!
"Scion FR-S, Toyota FT-86, Subaru BRZ platform performance and tuning guide"
Designed to be the ultimate enthusiast's vehicle, this new platform is not built from the factory for maximum speed. Rather than go for the standard sports car goal, the development of this vehicle was for maximum "fun factor" for the driver's experience. Controllable through a drift, the FR-S and BRZ bring back the good old days of JDM performance. Using a front midship layout, the vehicle is balance tuned for control at 53/47- not an even 50/50 weight distribution.
Using a new motor that strongly resembles the highly popular Subaru Impreza WRX and STi platform (EJ), the FA20 builds on the principles Subaru's perfected low center of gravity with Toyota's perfected wheelbase for slideways control. Comparable to that of other supercars, the FR-S COG sits approximately 460 mm (18.1102") above the pavement and features a drag coefficient of just .27 CD! Low to the ground and smooth in the air, this FR land-rocket is ready to dominate the streets and high speed challenges of the world.
When it comes to tuning and increasing the performance of these vehicles, there is a couple of different methods you can choose based on the amount of performance you wish to gain.
Note! The following recomendations are vague suggestions and require all supporting mods.
Maximum 600-1000 rwhp: turbocharged: engine and drivetrain swap to race or rally spec WRX / STi with RWD differntial mod
Street 400-700 rwhp: complete engine rebuild built for extreme RPM (10,000+) and nitrous oxide
Advanced 300-500 rwhp: small turbo at low boost, full bolt ons, 5-10 PSI with alcohol/methanol injection
Aggressive stock-300 rwhp: full bolt ons, i.e. exhaust, intake, tuning, ignition, rotating mass reduction, etc.
When modifying the FR-S or BRZ, you can choose to keep the motor stock or perform an engine swap. For those of you seeking utmost performance, the maximum tuning level for this vehicle will only be reached by swapping to a WRX or STi drivetrain because the engine's basic design is oriented towards forced induction. Why not use the stock drivetrain? To get the most out of any engine, you are only limited by how much boost you can run. More boost equals more power, but the engine must be designed from the ground up to take the addtional stresses caused by forced induction.
While the Subaru BRZ and FR-S may appear to be running the WRX or STi boxer engine, this is totally false and some may even go to the extent to call it "misleading". Everything about the FA20 is different than the EJ20 other than the fact it is a boxer engine. Check out the comparison below!
FR-S and BRZ FA20 engine specifications:
Displacement: 1998 cc
Bore and stroke: 86 mm by 86 mm
Compression ratio: 12.5:1
Standard EFI & direct injection
DOHC and dual variable valve timing, 16 valves
Maximum RPM: 7500
Subaru EJ20 2.0 liter turbocharged WRX engine specifications:
Displacement: 1994 cc
Bore and stroke: 92 mm by 75 mm
Compression ratio: 8:1
DOHC, 16 valves
Maximum RPM: 7200
As you can see, the two engines while similar in size and type are completely different. The naturally aspirated FR-S and BRZ engine features a slightly larger output but with a longer stroke and smaller bore and dramatically increased compression ratio. The turbocharged EJ20 features a smaller output, wider bore, and shorter stroke with a drastically lower compression ratio. The two engines vary in design because the EJ20 is originally designed for forced induction and the FA20 is not.
Can we boost the FA20 even though it wasn't designed for it? Of course! Even if you don't want to tear apart the engine and rebuild internals, you can still boost the FA20. However, most enthusiasts do not want to pull out a motor and change compression to satisfy higher boost levels but still want to run a turbocharger. While the FA20 may have a slightly longer stroke which increases EGT's, it can accept a very small turbo such as the TD-04 used on the stock EJ20 if set to very low PSI. By using a comparitive estimate, if the EJ20 can take 20 PSI of boost at 8:1 compression ratio, then the FA20 at 12.5:1 compression ratio can be said to take up to 12 psi at maximum.
The maximum PSI value is derrived by figuring internal cylinder pressures based on PSI x compression; but this figure is not definitive and is subject to environmental variables. To accomodate for heat, a maximum pressure of 10 PSI would be much more practical and yield combustion atmospheric pressures for the FA20 nearly 30 PSI below that of the EJ20. This type of setup would create an almost lag-free experience for the driver and maintain the original FR-S ideals without having to rebuild the entire engine.
For those of you seeking big volume and high PSI, a larger turbocharger can still be installed on the FA20 if you disassemble the motor and change the pistons to adjust compression ratio. Dropping the compression down to 8:1 or even 9:1 would allow for 20 PSI on a turbo up to roughly 800 CFM (20G, FP Green, etc). However, you will need to inject a chemical cooling agent and take care to watch EGT's! The slightly longer stroke will produce more friction and thus create more heat which can lead to knock. Injecting methanol or isopropyl alcohol is a great way to combat knock if you plan to run a larger turbo setup on the FA20.
How will the direct injection affect turbocharging the FA20? It will actually make tuning much more accurate and safe, but not allow for as much power as standard EFI due to the degredation of head strength. While the direct injection system is great for managing fuel and tuning for a big turbo, it is one more hole in the head and basically just creates another weak point. When you get past 1,000 CFM with turbos such as the Garrett GT40 or GT45R series turbo, it isn't just about maintaining fuel and mitigating knock; integrity of the engine's design becomes a major factor in longevity.
Due to the longer stroke, smaller bore, and direct injection the FA20 is not the best engine for maximum forced induction performance out of the FR-S or BRZ. Maximum overall performance will only be had by swapping the drivetrain to the EJ20 or EJ25 Subaru drivetrain as it was originally designed for turbocharging and is engineered to accomodate and mitigate the issues that arrise with forced induction. A shorter stroke with bigger bore equals less heat derrived out of friction, plus the heads are stronger due to using a standard EFI setup. While the bore may be larger and lead to cracking around the coolant jacket at higher PSI, aftermarket modifications such as "Subaru Block Supports" aka engine pinning can help rectify this issue and allow as much as 65 PSI and over 1,000 horsepower as seen here. For those seeking the ultimate FR-S or BRZ build, I strongly suggest swapping to a fully-built STi drivetrain.
In some scenarios, natural aspiration with nitrous oxide and maximum CFM can yield marginal results compared to that of forced induction. With forced induction, there is lag with decreases performance in certain situations that demand instant feedback and power generation. The FR-S and BRZ are designed from the ground up for maximum fun factor. That means the chassis design will react well to a quick responding engine thus pointing to nitrous and high RPM power as a solution for increasing performance.
Why not use a supercharger to keep the quick engine response? While supercharging can yield a quick source of power and flat dyno chart, due to the high compression ratio it is better to run nitrous if you are seeking maximum instant power.
Nitrous chemically cools and condenses the air molecules instead of mechanically compression, or "supercharging". Anytime you compress molecules, you will get heat. Supercharger only amplifies this effect resulting in increased intake temperatures that can lead to knock and predetonation. At high RPM, the last thing you want is to add warm air to a motor that is spinning at 10,000 RPM's or higher. There's enough heat already being generated within the cylinders to cause knock; you need to inject nitrous to not only supply adequate air but to absorb the heat being generated by the motor.
For the highest amount of power output from the FA20, I suggest running at high RPM and using massive amounts of nitrous oxide. This will create much more power than if you run a turbocharger, or a turbocharger with nitrous. Combined with Toyota's DS-4 direct injection and the boxer engine design, one could spin the motor to 10,000+ RPM with supporting mods while still using the stock compression ratio. While you may be tempted to use stock internals, I strongly recommend upgrading to forged and race-quality materials.
Supporting modifications for the high RPM naturally aspirated endeavor would include extremely detailed engine balancing, possible fuel system and ignition ugprades, and overall airflow improvement by both physical and chemical means. Valve upgrades are also extremely important! Springs must be upgraded with higher rates to accomodate the higher RPM.
When running at high RPM with natural aspiration, the challenge is not keeping up with fuel but keeping up with the supply of oxygen required to successfully complete each combustion cycle. Another notable quality of nitrous oxide is that it allows more air molecules per value of measured airflow into the motor without increasing atmospheric pressures withing the combustion chamber. Due to an already high compression ratio, this is extremely important. Direct injection of fuel and nitrous oxide should supply enough oxygen to create a quality, powerful burn and still yield the high power build that enthusiasts enjoy.
Nitrous will yield results that can range from mild to wild. If you don't want to run a high RPM and modify the engine internals to reflect your goals, you can still keep all engine internals stock and just run a healthy shot of nitrous and extend the rev limiter to 8,000 RPM. Toyota states that the engine and the DS-4 system is designed for high RPM reliability. The stock 7,500 RPM rev limit is not limited by mechanical reasons but is limited for warranty purposes. While the internals can take higher RPM, wear and tear will increase parrallel to the amount you raise the rev limiter.
Suspension, chassis, aerodynamics, braking, tires and weight reduction
Power isn't anything if you can't put it to good use. By keeping control of the vehicle and tuning for agility, the FR-S and BRZ can be built for either high speed or track domination. The low drag coefficient of the chassis combined with an race-quality STi drivetrain swap could indeed yield a 200+ mph vehicle with proper gearing. This would be a monster for top speed challenges and the infamous standing mile.
For those seeking the best track times, using a high RPM FA20 and electronically controlled ntirous oxide system would prove to be ideal when combined with proper weight reduction, chassis balancing to maintain proper weight distribution, aerodynamic improvements to downforce, and increased suspension systems designed towards specific track environments. If you are seeking a weekend warrior and daily driver, the turbocharged setup with around 10 PSI and chemical cooling would be ideal. It won't yield as great of a track time as the NOS and high RPM setup, but you will still dominate over naturally aspirated bolt-on racers.
Weight reduction can be found everywhere you look. If you don't need it, get rid of it. Switching out body components to carbon fiber will also offer an opportunity to modify aerodynamics and simultaneously reduce weight. Remove weight from the driveline itself is also very improtant! For every pound you take off the rotating mass, it is equivalent to releasing five to ten horsepower from the motor. Carbon fiber driveshafts, lightweight wheels, shaved and balanced crank, lightened pulleys, carbon fiber rotors, and a lightweight flywheel are great ways to improve acceleration and throttle response while also freeing up some ponies.
Stock weight: 2,690 lbs.
Maximum weight reduction estimated weight: 2,200 to 2,300 lbs.
When modifying the chassis of the FR-S and BRZ, we must remember that it is designed for perfect balance and predictability at a weight ratio of 53/47. As the power of the vehicle is increased, the balance of the chassis must be adjusted in order to maintain chassis homeostasis or the overall performance of the vehicle will be comprimised. If you start pulling weight off the chassis, use balancing counter measures to retain original cat-like agility.
Aerodynamics can be improved for two things; top speed and track performance. By adjusting downforce as needed, one can effectively "fly" the vehicle at low altitude. For high speed performance, this is of utmost importance. Without the proper aerodynamics and downforce, you'll lose traction and control once the vehicle's aerodynamics start to create lift in both situations; but this is drastically increased when the vehicle is used for maximum speed. Track aerodynamics aren't as vital and will only affect lap times. For high speed use, an improper aerodymanic tune on a vehicle can be fatal.
Keeping the vehicle stuck to the pavement is done by putting downforce on the front and rear of the vehicle. This is accomplished by adding parts such as wings, spoilers, and canards. Canards also help guide air away from entering the fender. While this may reduce brake cooling, it helps the vehicle to slip through the air at higher speed. The negative affect of canards upon brake cooling can be cured by adding brake cooling ducts to the front bumper. The overall goal of aerodynamic modification is to improve traction as much as possible while mitigating the loss of overall speed.
The job of a vehicle's suspension when oriented for performance is to reduce rolling friction and improve the vehicle's handling characteristics. If you have a suspension that is too tight, you will end up using some of your engine's power to fight the traversed topography. Each bump, lump, or change in direction of the road will slow down your vehicle and create an opposing force to forward motion; be it a tire moving up to compensate an increase in pavement elevation - or left or right while displacing energy during a turn. Proper damper, spring rates, and sway bar settings should be adjusted to reflect a balance of rolling friction reduction and handling.
FR-S and BRZ suspension systems:
Front: Macpherson strut
Rear: Double wishbone
Parts used to change or modify these properties would include coilover suspension, performance springs, sway bars, control arms, lateral links, cross members, tower braces, and other. Other forms would include custom ways of improving chassis rigidity or adjust the vehicle's lift during acceleration by adjusting caster. There's a balance of longitudinal weight transfer that must take place to create rear wheel traction, but that change in elevation which provides the weight transfer can't be too much or you will lose traction to the front wheels. There's a balance that is required for each driver, each track, and each vehicle. It is up to you as the builder to determine the "sweet spot".
Brakes and tires
Carefully choosing your brake system will play a huge role in overall vehicle attitude and capability just as much if not more than aerodynamics, suspension, weight reduction, and engine performance. A brake system is only as good as the tires! In order to make the most of your brakes, you must increase the contact patch of the tire while still maintaining proper pressure upon the pavement from the vehicle to maintain traction. It isn't always "wider is better"; too wide or skinny of a tire and you'll lose braking and handling values exponentially.
An ideal tire and wheel setup for circuit style and high speed driving would be a staggard setup with 18x8.5" in the front and 19x9.5" in the rear. A slight strake will help retain traction in the rear during corning and also provide excellent acceleration traction while minimizing front wheel drag. For the drag strip or short street style racing, 16" wheels all around staggared the same as before, but with wide slicks in the rear and skinny tires up front.
Brakes should be tuned according to the limitations of your tire and how much you need to reduce brake fade. The bigger the brakes, the more metal there is to absorb and distribute heat and reduce brake fade. Brake fade is typically only an issue for track style driving, cornering, and other aggressive scenarios that require rapid deceleration. If you feel your brakes starting to get a slushy feeling after repetive use, you are overheating and thus experience brake fade. This can be controlled by adding a "big brake kit".
Which big brake kit or brake upgrade kit should you choose? How much you need to upgrade your brakes should be a constant value linked directly with your tire's capabilities. Wider, sticker tires; get bigger brakes. If you don't change your tires, don't bother changing the brakes! Stock tires are perfect for stock brakes.
Tuning the FA20 will follow the basic rules of tuning. You must find the balance of air to fuel ratio and timing in regards to knock count. The more aggressive you can tune your timing with a leaner mixture the more power you will make. For example, the perfect air to fuel ratio for an EJ20 or EJ25 turbocharged boxer engine is 11.2 to one. That's 11.2 parts air to one part of fuel; a rich mixture designed to cool the engine from the heat created by the turbocharger and combustion process. The same applies to naturally aspirated engines but under much leaner conditions.
Scaling the mass air meter or MAF will accomodate for larger intakes and higher RPM air flow values. Scaling of MAP sensor will also adjust fuel flow. If the stock rev liter is set to 7,500 RPM's, the volume of that air moving past the MAF and the pressure in the manifold will play a key role in what the ECU decides is a good AFR. When more air comes into the motor, it adjusts the fuel flow accordingly to maintain the ideal AFR as predetermined by "fuel map" tuning tables and scaling values.
The new platform is a vast land of tuning opportunity thanks to an already aggressive design from factory. I believe that the FR-S / FT-86 / BRZ will be an extreme force of incredible speed once fully built and modified. Questions? Comments? Leave a comment in the space below or visit http://www.facebook.com/SubyPAL to contact me directly. Drive fast and reckless!
By Michael Berenis