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How to Plan a 2015+ WRX FA20DIT Build Blog Feature

By: Alan Jackson on October 5th, 2016

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How to Plan a 2015+ WRX FA20DIT Build

Subaru WRX / WRX STI

So you have just purchased your dream car and you are now looking to make it your own. Where do you start? Where do you go? What are you going to do? You need to sit down come up with a goal, prioritize, plan, and then realize your goals. This is something that is both very easy, and very difficult at the same time.

So often in my own vehicle modification filled history, I have had an idea in my head, but I never really sat down and thought about what I really wanted a project to end up as. I flew by the seat of my pants and I ended up spending money twice by not buying the right parts the first time. I would have to do the same work multiple times because I didn’t put similar parts together. While I still ended up with a pretty sweet car, looking back, I could have done it for a lot less money and with a lot less down time.

In the relatively short period of my life that I’ve spent modifying cars (roughly 7 years), I have had a 500whp Mazdaspeed 3, two Mazdapseed 6’s, an 04 Yamaha R6, a 2012 Yamaha R1, and now a clean slate (almost completely stock) 2016 WRX. As I’ve come along, each vehicle has become more and more organized and I’m to the point now where I’m somewhat OCD about it.

TMT_MS3_PERM.jpgMy Mazdaspeed 3 was the first car I’ve owned that was worth modifying. I started out with a Cobb SF Intake and ended with a Top Mount/Rotated Turbo Kit sporting an HTA3586 courtesy of PERM Tuning. The car made 503whp before I sold it. Between that Cobb SF intake and the 503whp dyno plot, there were a lot of mods that came and went, and looking back, I see where I could have focused my efforts and spent less time and money doing work and buying parts twice.

On my next series of vehicles I made a point to think further ahead. I didn’t mod the R6, but I did mod the R1. I bought parts that made sense for what I wanted and set it up in the first stage of parts to be ready for the second stage of parts.

It was during this time frame that I also acquired my first speed 6. It had a blown engine and so I researched and found the engine I would use to replace the blown one (Mazda OEM Reman Long Block). Then I planned a few mods to do during the swap based on my future goals and what would be convenient at that time.  However my plan was foiled by an offer to buy the soon to be repaired car and so my future plans were added to, and a full big turbo kit was lined up to go in with the new engine. This saved the new owner future money and time. The car was put back together, tuned, and then delivered.


Now, after some time spent on two wheels, I’m back in a cage and in a 2016 WRX and the planning is well underway. There are so many things that can be done to this car and there are so many different levels that it can be taken to, so having a plan for the build is the first thing I wanted to do before I ever spent a dime. 


Set a goal:

The goal is the somewhat vague picture that sets the plan in motion. To start with my WRX, I have to sit down and figure out what I want from this car. It is going to be a daily driver for the foreseeable future, so reliability is extremely important to me. In other words I’ll be sticking to modifications I know will be safe on the stock block. That isn’t to say I don’t accept the risks of modifying the car, but I will be doing so with the intention of maintaining as much reliability as possible.

My goal for the car is to make as much power as I can reliably on the stock engine. I’ll be aiming for 350 to 375whp. I want the car to perform as well in the corners as it does out of the corners, but I don’t want to sacrifice too much ride quality in the process. I also want it to look as good as it performs.

While I’m not aiming to have the fastest FA20DIT powered WRX in the world, there may come a time in the future where a motor build comes into play and more power will be desired. So, I will also be keeping this in mind as I move forward.


After you’ve established a goal, you can start to prioritize your wish list and order of operations.

For me, my first priority is power. Being at a much higher altitude here in Denver, CO, my car runs much slower than everyone else at or near sea level.  In order to reclaim some of that lost power, my first priority is going to be based around the engine.

Cobb_AP.jpgBut even knowing that I want to start with the engine isn’t good enough. Where in the engine should I start? Since I know that pretty much any power mod I install will require tuning, my first choice needs to address that. I chose the Cobb Tuning Accessport. Not only does this device allow me to make more power immediately, it also opens the door to making more power in the future as well.

When making your priority list, you may also want to consider any shortcomings your vehicle might have. In the world of Volkswagen, Mazdapseed, and other DI cars, that shortcoming is the High Pressure Fuel Pump (HPFP). For me and my FA20DIT, it is a rather nasty boost spike. So another high priority modification for me is a boost controller.  

Even though power and performance mods are a higher priority for me than suspension and handling mods, that doesn’t mean I haven’t thought about it. I have those prioritized as well.

Once you have a general priority list of what is most important to you, you can begin to assemble your plan.

The Build Plan:

A build plan should be a complete map of your projects priorities that will help lead you towards accomplishing the end goals.

It should follow the path of the priorities you laid out in a way that helps prevent you from spending money or doing work twice. For instance, on the Mazdapseed 3, there are a lot of intake upgrades. Most people run the Cobb SF Short Ram Intake or a JBR Power Path that fits with the stock turbo and offers a decent performance boost. However, as they get further and further down the rabbit hole of modifications, they decide to upgrade the turbo and find that the intake they already have is not going to cut it. For one, it won’t fit the compressor inlet of the new larger turbo, and two, it won’t flow enough air to expose the new turbos true potential. Now they have to purchase another intake.

With a plan in place, they would have known the bigger turbo was coming and would have purchased the larger intake from the beginning. Even though it isn’t necessary on the stock turbo, it would have saved them purchasing the same or similar part a second time.

For me, I will be going with a 3” intake option on my WRX because I know that little voice in the back of my head is eventually going to talk me into a slightly bigger turbo and I want to have parts on the car that will work best with the upgrade.  Regardless of whether I do or not, it'll allow for better flow from the stock turbo and at the end of the day, I still need to buy an intake anyway.

So without further ado, here is my build plan for the 2016 WRX.

My goal is a daily driver that will push around 350whp, but with the capability to hit 400whp should I decide to go a little further. My priority is power first, with suspension and handling to follow. I will also have a few appearance mods thrown in here and there. So here is the plan.

Step 1: Tuning and Problem areas

I need to be able to tune the car for the upcoming mods.  I also know that the WRX tends to suffer from a rather large boost spike, so for step one I’ll be going with a Cobb Tuning Accessport and a GrimmSpeed 3 Port EBCS.             GS_EBCS.jpg

Aside from the boost spike, the other factory flaw that I felt the need to address at this time was the EGR System. Since my car has such low miles on it, I wanted to go ahead and remove the EGR system in order to keep my valves nice and clean. 



Step 2: Mo Powa

            With what I’ve observed from others who have gone before me, I know that the J-Pipe is the next biggest bump in power. And since I want to maximize my efforts, the GrimmSpeed J-Pipe is going to be the next purchase.

It would typically be at this time that I would also install a cat back exhaust to complete the exhaust post turbo. However since I am on a stricter budget at the moment, the stock cat back will have to stay for a bit longer.


Step 3: More Air

With the exhaust side opened up, I now want to get the intake side to breathe easier. That means installing an intake. Since I’d like to eventually run a stock style turbo upgrade on my WRX, I would like to go ahead and purchase an intake that I think would work well with that factory frame turbo upgrade. The Cobb Big SF Intake is what I'm going with.            Cobb_Big_SF_Intake.jpg

Since I’m going to be working with the intake, this will also be a good time to upgrade the leaky stock bypass valve. After watching Boomba Racing’s test video for the 2015+ WRX, I was sold on their upgraded bypass valve that is pressure tested to 100psi.  If you are plagued with the leaky stock valve, then this mod will free up some lost horsepower for sure.




Step 4: Cold Air

GS_TMIC.jpgNow that my car is breathing, it's time to make the most out of the air it's pulling through. That is where an upgraded intercooler/aftercooler comes in. There are quite a few options for this and it starts to get more and more difficult to nail down what I want. I like the fact that Killer B’s Aftercooler allows you to keep the factory engine cover, but GrimmSpeeds upgraded top mount intercooler with the addition of some fancy vents helps to force more air through the intercooler and therefore improve the performance even further.

My other option is a front mount intercooler and I personally prefer the TurboXS unit. It isn’t too big and will be more than enough for my power goals. However, since I don’t plan on going past 400whp with this car, a FMIC may be too much for me. And yes it can help with heat soak, but with the GrimmSpeed’s ram air effect, it may not be enough of a problem to justify going the FMIC route. Plus, I know that GrimmSpeed’s TMIC is more than capable of supporting my power goals and with there not being a turbo hiding underneath the FA20DIT’s top mount location like they do on the EJ’s, the GrimmSpeed TMIC and charge pipe seems to be the clear choice for me.

With the intercooler being removed/replaced, and my wish to improve the airflow as much as possible, this becomes the opportune time to perform the TGV delete mod. While these don’t seem to have too much effect on peak gains, they do result in a significant improvement in area under the curve. So some Radium TGV Deletes will be instore at this time.


With the power that this setup is now capable of, we are touching on another factory issue… The pitch stop bracket on the firewall. I’ve seen too many of these fail to ignore this and for that reason, it is at this time while the intercooler is off that I will also be installing the Perrin Pitch Stop Brace and because of convenience, I will pick up a Pitch Stop Mount at this time as well.



Step 5: Stopping Power

I would be lying if I told you that I was completely happy with the factory brakes on the WRX. There is probably nothing I want more than a set of STI Brembo’s to make for a nice little factory upgrade. The reason I have decided to wait so long to do them in my build plan is because I want to get the most out of my factory setup first. I don’t necessarily want to replace a perfectly good set of brakes, so by the time I get to this point in my build plan, my brakes will be due for a change anyways, and the cost will effectively be less that way.

Radium_Master_Cylinder_Brace.jpgWhile I’m upgrading the brakes, I’ll also be upgrading the brake lines with a StopTech Stainless Steel set. And while we are talking brakes, another good mod to do that fixes another factory issue is the Brake Master Cylinder Brace. I’ll be going with the Radium unit.




Step 6: The Low Life

First of all, I’m not about the low low life. I like function over form and will be going with a set of coilovers based on their performance rather than their ability to drop my frame to the ground. Because they retain the inverted strut design, I’m heavily leaning towards the HKS Hypermax Coilovers.


I will also be slapping on some new wheels and tires at this time. I know the look I want and while I’m not going into too much detail here, I have a set of 18x9.5” wheels picked out that will be getting rapped in a nice meaty tire. I don’t want to go too wide on the tire because this is still a  street car and I need to stick with my daily driver goal.

Step 7: The Stiff Life

While it is tempting to get this all at once with the coilovers and wheels, budget dictates that I wait. So I’m dedicating a whole step to sway bars and adjustability. For sway bars, I’ll be going with the Whiteline adjustable rear sway bar, though I haven’t fully decided how stiff yet. I also haven’t decided if I want a front sway bar yet because I tend to like a car with a little rear end bias.

For adjustability, I’ll be going with some adjustable lower control arms from Whiteline. After all this is installed, I’ll be going to get an alignment to dial it in perfectly and that should take care of my suspension plans.

Just because you set a plan doesn’t mean you have to stick with it perfectly. Goals can change, but if you plan far enough ahead, you can adapt to the changing goals without having to completely reformulate the plan. However, having the plan in place will give you a clearer picture as to where you are going and allow you to make better decisions when you do come to a point where your goals might change.