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Author: Julius Bloem  Date Posted:31 March 2020 

2013 WRX Flex Fuel Build David's GV WRX Shows what's possible with a well-comprised bolt-on upgrade package and E85 fuel. For this build we selected the Possum Bourne Motorsport Stage 6 package plus flex-fuel conversion to allow use on both E85 and regular 98 fuels.

The BIGGEST power WRX we've ever built that still uses the stock block and stock turbo

David and his 2014 Subaru WRX gave us the opportunity to push the limit on the stock block engine and factory turbo by making use of modern technology, power-adding parts and the wonderous E85 fuel. 

The result was the most power we’ve ever seen from a stock WRX engine using the stock turbo.


We knew that the EJ25 long block and stock turbo is capable of a lot, however there are a few weaknesses with the engine and plenty of restrictions with the external components that would need to be replaced. To allow the engine to flow well enough to make some power, we decided to go for a PBMS Stage 6 package, which we’ll delve into in a moment. To aid power and help the engine perform reliably, we also worked with David to convert this WRX to run E85 by implementing a flex-fuel setup.

PBMS Stage 6 with E85 Conversion

The package we’ve put together is the PBMS stage 6 which suits a 2008-2014 Subaru WRX. A Stage 6 package includes an upgraded downpipe, cat-back exhaust system, upgraded turbo intake pipe, cold air intake, intercooler upgrade, TGV deletes, in-tank fuel pump and PBMS tune.

An E85 fuel conversion requires a fuel system upgrade and flex-fuel conversion kit to give the vehicle the ability to the run on both regular pump and high-power-producing E85. 

Engine and Turbo

As we’ve pointed out, this car has a stock EJ255 WRX engine and stock VF52 turbo. To help keep these components reliable under load, we always use high-quality oil like Motul 8100 X-Cess, Motul Sports or Motul 300v, a genuine Subaru oil filter and shortened service periods as it’s running E85. E85 can cause degradation to your engine if you aren’t cautious. Click here for oil, filter and maintenance products.

It should also be noted that the EJ255 and EJ257 have a number of inherent weaknesses, so whilst we have been able to minimise the chance of issues by using quality products, tuning with engine conservation in mind and executing a plan to prolong engine life, there is risk involved. From our experience, it is possible to extract significant power from these engines whilst maintaining reliability in many cases, we have seen examples where premature failure has been caused by a lack of regular & suitable quality of maintenance, poor engine condition prior to modification, overly aggressive driving and low/inconsistent quality of internal engine parts from time to time. When pushing the limits, we suggest you plan to do an engine build or upgrade the components being pushed in the future. 


To unlock exhaust flow from the engine, we’ve fitted a high-quality Invidia Q300 Cat-back and Invidia High-Flow Downpipe. This 3 inch systems fit incredibly well, look good and are made from stainless steel so will last a long time. The Q300 is designed to be used on a daily-driven vehicle, so provides the perfect balance between a nice exhaust rumble, without being too loud.

Click here for exhaust systems and headers.

Cold Air Intake 

To unlock flow into the engine, we started with a Cobb cold air intake. The design ensures that the engine only sucks cold air from outside the engine bay and the larger filter means less restriction for air entering the intake pipe. You can really hear this intake system at work. Although we've gone for a Cobb on this particular example, our favourite intake is the Process West Cold Air Intake. 

Turbo Intake Pipe

The turbo intake pipe has been upgraded with a Perrin intake pipe. This is the pipe that runs between the Cobb CAI and the turbo. This upgraded pipe is larger in diameter and reduces the restriction of air entering the turbocharger.

TGV Delete

TGV Deletes have been fitted in place of the Tumble Generator Valves which are a huge restriction for air in the intake manifold, entering the engine. 


Under the hood you can see we’ve fitted a Process West Verticooler. These intercoolers are the most efficient top mount intercoolers, that are mounted vertically to give the largest possible surface area. The under-bonnet ducting forces air through the verticooler to get it cooling really well. The main advantage of a verticooler or top mount intercooler over a front mount intercooler is the shorter intercooler piping which really helps response. With a verticooler fitted, this intercooler is able to cool the boost far better than the stock intercooler, whilst maintain response which is a slight disadvantage when fitting a front mount intercooler.

Fuel System

We’ve done a full fuel system upgrade to suit the demands of E85, whist requires additional flow and needs to be resistant to the corrosive alcohol content. In place of the factory fuel pump, we have fitted a Deutschworks DW65C in tank. This feeds an under-bonnet Radium Surge Tank with a hard-wired AEM340 LPH pump. This hard-wiring ensures maximum voltage and performance from the fuel pump. The beautifully engineered surge tank also has an in-built fuel pressure regulator.

To deliver fuel to the engine we’ve fitted Injector Dynamics 1050X injectors. These are high-quality injectors that are proven to work well with the sensitive factory ECU, and come with all of the injector data required to get the best drivability you can achieve on a setup like this. 

To send the ECU the required information to run both E85 and 98 fuel we’ve fitted and wired in a Zeitronics Flex Fuel Sensor kit. 

PBMS Tuned using ECUTEK

This car has been PBMS tuned by our tuner KB here on our rolling road dyno, then the tune validated on the road. Like all of the cars we tune at PBMS, we used the 9-step tuning method to gain the best results. Check out our 9-step tuning video so you can see what makes our tuning different from most other tuners.  

We tuned this car using ECUTEK because this is a professional software that has been fully developed for use with E85 flex-fuel function. 

One of our favourite parts of ECUTEK is their RaceRom feature. We’ve installed and calibrated RaceRom features on this car including the FlexFuel system, flat foot shifting and launch control.


We’re going to note that we also fitted a Soutbend Racing Clutch Single Plate including Lightened Flywheel. The upgraded clutch was done as a precaution as the factory clutch would have been at its limit and the lightened flywheel will help the engine to rev more freely when enjoying the new power. 


You’ve all been waiting to hear what the results are. We all know a stock WRX has a bit of pep and provides plenty of fun, but this package has taken this car to the next level. 

Dyno Power

From stock, these cars produce around 150kw at the wheels, on a good day. On 98 this car produced around 240kw, which already made for a rapid car. E85 fuel took it to the next level when this car produced 270kw at the wheels. That makes it the most powerful WRX or STI we’ve ever tuned on a stock turbo. 

Stock Turbo WRX E85 Flex Fuel

Performance on the road

Even though peak power is important, where this car really shines is with it’s wide powerband. It’s super-responsive, with power right from idle and full boost seen before 3000rpm when you’re having fun on the back roads. This has no comparison to stock, it feels like it’s got twice the power, everywhere! 

How good does it sound?

You can really hear the engine with the new exhaust and intake system, it has a tough note when you want it to, but at the same time, it actually sounds quite respectable if you’re driving around town in a respectable manner. 

Engine Bay

From the outside, the only difference you can see is the nice stainless/titanium exhaust tips if you know what you’re looking for. Under the hood, you can certainly tell there are some aftermarket parts fitted, however, they are all top quality and fit very well so it’s a tidy affair that actually looks a lot better than stock. The bonus with all of this sort of modification is that if you ever wanted to, the parts unbolt and are completely reversible.


We’ve completed this setup with quality parts so it will last a long time. As we’ve already covered, running E85 is a good way to make power whilst pro-longing the life of your engine, just keep in mind regular oil changes are required. If this car was going to be used on the track at all, we’d be recommending upgrading to a PBMS baffled sump. 

Did we achieve the goals?

We’re incredibly happy with the end result of this project. We were expecting it to make some good power and were presently surprised that it’s ended up producing the most we’ve seen from a factory WRX turbo. David, the owner is also over the moon with how it performs.

How could we improve the setup

If we wanted to put this car a little harder, the first thing we’d need to upgrade would be the factory turbo and likely the fuel pump inside the surge tank, then we could push for the 300kw+ mark. At that point, the stock EJ255 engine would definitely be at its limit, so this factory turbo setup is great for most people.

If we were using the engine on the track we’d highly recommend fitting a PBMS baffled sump to prevent oil surge that could damage the engine. If we were looking to push the gearbox, perhaps with any drag racing or the odd launch, we’d be fitting some gearbox blast plates as this helps to strengthen and reinforce the stock WRX 5-speed transmissions. 


If you stepped out of a stock car and into this, you wouldn’t believe that it still has the same engine and turbo. It’s a completely new beast that will be at home on the road or the track.

If you’re interested in having any of this work done to your car or you're after any parts, please don't hesitate to contact us.

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