Let’s first go over how the wastegate and actuator work. The purpose of the wastegate is to maintain a particular boost pressure at the intake manifold by regulating the speed at which the turbo spins. It does this by regulating a pathway/door which diverts exhaust gases AROUND the turbine. The faster the turbine spins, the more boost the turbo generates.

The more exhaust you divert through the wastegate (the more you open the wasetgate door), the more you slow the turbo down and this is how you lower boost.

This wastegate is pushed open or held closed by the wastegate actuator and a number of other variables such as exhaust pressure. The actuator is a boost actuated diaphragm inside a canister with a rod sticking out as shown below. Boost pressure is applied to the canister and once the boost is higher than the spring pressure inside the canister, the wastegate actuator rod starts to move and open the wastegate.

The actuator doesn’t open the wastegate fully at a given single pressure. It starts to open it at a cracking pressure (also known as spring pressure) and then the more pressure you apply to the canister the more it opens the wastegate door. The amount of boost pressure this canister sees is regulated using the boost control solenoid which is controlled by the ECU and the tune running on the motor.

In spite of the ECU controlling boost pressure going to the actuator, the amount of boost a turbo can hold at any engine speed (RPM) is determined by a large number of factors. Some of these are the turbo itself, the engine displacement, the flow parts installed, the ambient temperature and more importantly for this discussion the spring inside the wastegate actuator and the preload on this spring. On OEM wastegate actuators we can’t change the spring inside the canister because they are sealed. On aftermarket actuators and external wastegates we can change the internal spring. Therefore, the only aspect that we can change on the OEM actuator is preload. Shortening the wastegate rod using the adjustment screws adds preload to the internal spring. The reverse removes preload. When you increase the preload you do two things. One is that you increase the boost pressure needed to start opening the wastegate. The second is that you  lower the opening range of the wastegate door.

Increasing preload or changing the actuator with a higher spring pressure model (such as a Turbosmart pictured below) results in more boost! And that’s a good thing – right?

Well – the answer is a little more complicated.

First of all, keep in mind that making these kind of changes almost always requires that you get your tune adjusted. Reliable boost control is extremely important for the reliability of the engine. Secondly, you can introduce boost response issues such as boost spiking and boost creep. Most OEM turbos won’t suffer from these issues but it’s very important to make sure the boost of your vehicle reacts smoothly and is under control after you make any changes to the system.

Finally you have to make sure that more boost actually results in more power. When building and tuning a car, you have to look at the engine as a package. Changing boost will affect other variables such as fuel requirements, cooling requirements, and whether or not everything is still working efficiently.

A Turbosmart actuator on a Focus ST with the OEM K03 turbo will hold over 20psi to redline for example. The OEM actuator will only allow 13-15psi. In experimenting with this we found that holding more boost to redline makes the car quite knock prone even when using E85 mixes and mild timing. The turbo looked to be well out of its efficiency range and we kept dropping the boost until we were at 18psi at redline. Even then the motor was knock prone especially up top. Increasing the boost on the OE turbo in the upper RPM (past 6000RPM) is not worth the penalty in heat and timing reduction especially on pump gas.

Another interesting bit of information was that without modifying the fuelling tables the short term fuel trims (STFT) became quite negative in the upper RPM (in orange in the graph below). The car calculates fueling based on boost pressure/manifold pressure and this drop in STFT indicated that for the boost measured the airflow was actually less than the ECU was calculating and expecting.

This is another indication of the lack of efficiency of the K03 at those boost levels. The higher we pushed it in terms of boost, the more negative the trims.

The Virtual Dyno plot below shows a similar story. This was on E85, stock actuator (red) vs Turbosmart (blue). There is a big difference in boost which results in a nice midrange increase in torque. However look at 6000 RPM – there the increase in boost makes no difference in power and we are probably driving the OEM turbo much too hard and reducing reliability. We had to reduce timing by around 6 degrees up top to keep the car from knocking even on 3.5 gallons of E85 mixed in the tank. Things got toasty and inefficient.

Conclusion on this? A little bit of extra boost is going to give you a nice bump in midrange torque. Adjusting the preload on the OEM actuator on the Focus ST carefully can give you a little bit more boost, but don’t overdo it. If you modify the boost control system and are not sure of what to look for make sure you have your tuner look over the data coming from the engine after the change. We offer the datalog report service for situations such as these.

Keep a very close eye on knock/timing corrections. This is especially true on pump gas as more boost (especially past 6000RPM) results in more knock. If you have poor pump fuel this may not be worth the penalty you will take in terms of timing and heat/inefficiency. Finally, driving the OEM turbo (or any turbo) to inefficient boost levels is likely to affects its long term reliability.

Drag racing is something a lot of the ST community enjoys so here are some of our findings in drag racing the ST.

We didn’t take the car drag racing when it was stock or close to stock. At our local track a stock ST runs in the 14s on street tires. You can take a stock ST and drag race it all day long without worrying about breaking things or being overly hard on the car. Seat time will improve times more than anything. At the same time keep in mind that the low profile tires on the ST are made for cornering and not drag racing. You will get lots of wheel hop and 60 foot times will be high. This doesn’t result in the best overall quarter mile times.

As you increase the power, you will see incremental improvements especially when coupled with seat time and traction! Keeping the stock K03, a car with E85 or WMI and all bolt ons and a good tune is capable of low 13s at around 105-107mph with the right tires. For tires you can either get a drag radial like the Hoosier Drag Radial DOT tire or something even more aggressive like a Quick Time Pro.

The Drag Radials are sized the same as normal street tires. A common size is the P245/45R17 (https://www.hoosiertire.com/specdrag.htm#DOT Drag Radial). These need to be fitted to a set of 17″ rims. I recommend getting the smallest diameter wheel possible (on the later ’14s and ’15s that’s a 17 rim to fit the brakes) Remember that in drag racing the most important part of your run is the launch and 60 foot. This is why people talk about it so much. Whatever you save on your 60 foot will double by the end of the quarter mile. For example if your 60 foot is 2.2 seconds and your quarter mile is 14.0; if you cut that 60 foot to 2.0 seconds your quarter mile time will drop to 13.6.

This is why drag tires are so important. If you have lots of power and can’t put it down, you won’t have an ET that is representative of that power level. Most people on street tires will have a 60 foot of 2.4-2.2 seconds. On drag radials you can consistently be in the 2.0-1.9 range. Your trap speed (if you don’t miss shifts) is representative of your power level.

Jeremy, one of the guys that works for us from Memphis uses drag radials and here is one of his runs. He has a lot of track experience and consistent times. He is running a GTX2867 and 2 gallons of E85 in this run.

For my car, I went with a more aggressive tire – a Hoosier QTP slick (https://www.hoosiertire.com/specdrag.htm#QUICK TIME PRO). The size is 26 x 9.5 x 16. It is a little tall even for 400whp. It hooks up very well and I run 12-14psi of pressure in the tire. Since it is on a 16″ rim there is a lot of sidewall flex meaning it can absorb the impact of a launch quite well and not slip. This tire should be able to get well into the 1.8-1.6 60 foot range depending on how aggressive you launch.

When we took the car to the track the first time, it was already on the big turbo (ATP GTX2867), Stratified aux fuel, etc. It was making around 380 ft lbs and 400whp but flat foot shifting was not working as it should have been. With a launch around 4000 RPM, managed a 12.6 second run.

Knowing there is more in it, sorted out some of the FFS issues, increased torque and went back. While the car was making a solid 400 ft lbs+ of torque the clutch was still stock with 23000 miles on it.

On the first pass at this power level, the clutch finally couldn’t hold the torque.

The shock delivered by the 5000 RPM launch overwhelmed the OEM clutch which is not surprising. Later that day once the car cooled off, the clutch would again hold fine on street tires. So on slicks, at 400+ ft lbs of torque launching can overwhelm the clutch. Otherwise and so far everything has been holding together great. We have an upgraded COBB rear motor mount as well as Bilstein B14 coilovers installed which help keep the car and engine planted while still being very civil in daily driving.

What’s next? A Spec Stg3+ clutch (sticking with the OEM dual mass flywheel) and a Quaife LSD (this is more so for auto-x). The engine has been very reliable so far even with the abuse of R&D as well as daily driving the car which is great to see. While the ST is better suited for going around turns, you can certainly have a lot of fun with it at the drag strip. So get out there and race your ST, you won’t regret it!

Those of you reading this are most likely at the point where you’ve reached the limits of your K03 Turbo and are hungry for more. The OEM K03 is able to deliver between 250-290whp depending on setup but beyond this a bigger turbo is needed. Thankfully, the aftermarket is full of solutions and StratifiedAuto is here to help you get to your goals whatever they may be.

Before we get started, here is the I want power now show me what I need version of this post (tl;dr):

• Stratified Big Turbo Plus Tune Package (Most popular is GTX2867R)
• Stratified Aux Fuel Kit (If E85 or Race Gas Available)
• FMIC, pick one with a good core like ATP (Garrett Core) or CP-e (big core)
• Quality Downpipe
• Aftermarket Intake System
• Water-Methanol Injection (If E85 is not available)

Now onto the details. One of the most common questions we answer is “Which turbo is right for me?”. This is a difficult question as the answer depends on your goals. It is very important to have a clear understanding of your goals before you can set out to reach those goals. A GTX30xx turbo can make 500 whp, however, it will be hard pressed to make much boost before 3,500 RPM. On the other hand, a GTX2860 can reach over 20psi by 3,000 RPM but it will run out of steam up top compared to a GTX3071 turbo.

There is no golden ticket, no turbo will spool like OEM and flow very well up top. That being said, we have enough turbo options that get pretty darn close and maximize the area under the power curve. When looking at turbos for the Ford EcoBoost the comparison is generally between the Borg-Warner EFR and Garrett GTX. The Borg-Warner EFR (Engineered For Race) turbos are more expensive, however, they feature very light weight rotating components which means they are very responsive. The Garrett GTX turbos are a bit less expensive due to a heavier exhaust wheel but they have the ability to bolt on an external wastegate (with the ATP exhaust housing). The GTX also have billet compressor wheels helping them spool quicker and flow more than the older GT series. Garrett GTX turbos are also very reliable and you do not require a new downpipe, charge pipe, and intake which are needed for the EFR.

So, the first question to answer is am I ready for a big turbo?

The minimum we recommend when upgrading the turbo on your Focus ST would be an upgraded intercooler, a high flow air filter, BPV/BOV (for Garrett turbos), and a downpipe. Those of you looking to make more than 350WHP are going to either need a Stratified Aux Fuel Kit or water-methanol injection. We recommend the Stratified Aux Fuel Kit for customers who have exceptional fuel or E85 readily available. For customers who are octane limited and do not have E85 available then WMI is the way to go as it helps bump the fuel octane while also helping with fueling. You can also run both systems for the ultimate fueling and cooling capabilities.

The second question is often Full-Race EFR or ATP Garrett?

Here are some benefits of each kit: Full Race Borg-Warner EFR Kits:

• Integrated BPV
• Big internal waste gate
• Quickest spooling, high flowing
• A little less compressor efficiency compared to the Garrett GTX
• Price includes downpipe, charge pipes, and intake. (Not compatible with downpipe, charge pipe, or intake from a K03 powered turbo car)

ATP Garrett Bolt-On Turbo Kits:

• Billet compressor wheel for quick spool and high flow
• Compatible with OEM fit intakes / charge pipes
• Compatible with external wasteage
• Extremely reliable turbo
• Requires an external BOV

The long and the short is that the EFR turbos are more expensive, however, they generally spool faster than an equivalent Garrett. The Garrett Turbos are more affordable and a little more efficient, however, will spool a little slower than an EFR (of similar size), and require an aftermarket BPV. Most people who already have a bolted car prefer the GTX because they can reuse their parts. If starting from scratch with a bone stock car, the EFR kit includes many of the needed parts (downpipe, intake, charge pipe).

One of the last questions asked is “Do I need to build my block?”

Luckily for us these EcoBoost motors are robust and reliable. How long your motor survives and how much power it can handle will depend on many factors, however, we can still look at the trends and draw a conclusion. Up to around 400WHP things look to be very reliable on a mainly street and drag race car. Even the OEM clutch holds reasonably well up to 400 ftbs/400whp. A poor tune and heat are the biggest enemy of reliability. Ring lands are the first to suffer and these failures are generally the result of too much heat, detonation, and/or poorly setup tunes and parts. If you plan on taking your big turbo ST to a road course make sure the brakes, tires and engine cooling are up to the task. The OEM cooling system must be augmented with at least external oil cooling once you approach the 300whp mark. Our development vehicle which sees daily R&D abuse has been extremely reliable which along with data from many other cars indicate that the Focus ST is reliable and a very good big turbo candidate.

Now, on to the specific turbos:

Below I’ve listed the common Focus ST turbo upgrades from each company in order from smallest to biggest. A smaller turbo will spool faster but flow less than a bigger turbo. Also, remember that anything over ~350whp on a Focus ST is going to require either need a Stratified Aux Fuel Kit with ethanol blended fuel or water-methanol injection.

Full-Race BW EFR Turbo Options:

With the BW EFR turbos the first two numbers are the compressor size while the last two are the turbine size. The turbine size is what most strongly affects how the turbo spools. The compressor determines how much the turbo can flow – its top end potential.

1. EFR 6258:This turbo is the smallest offering available with the Full-Race EFR kits making this the quickest spooling turbo available. This turbo is good for up to 375 whp on a Focus ST with response that is closest to OEM.This turbo will spool faster and flow similarly to a GTX2860 (full boost below 3,000 RPM).

2. EFR 6758: This turbo uses the same turbine as the 6258, however, features a larger compressor. This means you will still get excellent spool while flowing up to around 400 WHP on a Focus ST. Expect spool to be similar to the GTX2863 (or around 2-400 RPM later than the 6258) and flow to be between the GTX2863 and GTX2867.

Behold the Borg-Warner EFR 6758 and Full Race Focus ST Downpipe

3. EFR 7163:This is the largest turbo EFR currently offers with their Focus ST kits and features a larger compressor and turbine than both the EFR 6258 and EFR 6758. This is the same turbo which made 459whp on a Stratified Tuned Focus ST. Expect spool similar to the GTX2971 (full boost ~3,700 RPM) and flow between the GTX2971 and GTX3076 turbos.

Stratified Tuned Focus ST making 459 WHP with an EFR 7163

Garrett GTX Turbo Options:

The GT series turbos have been omitted from this discussion as they are older technology and not a common choice for the Focus ST. Behavior of the GTX turbo is similar to that of the GT turbo, however, the GTX turbos are more efficient across the board. For those of you who did not know, with the Garrett turbos the first two numbers are the turbine size and the second two are the compressor. So, for example, all GTX28xx turbos will have the same turbine. The turbine size is what most strongly affects how the turbo spools and compressor determines the top end flow potential.

1. ATP/Garrett GTX 2860, 2863, 2867, 2871: Featuring a 10-blade compressor wheel and ball bearing center cartridge these turbos provide quicker spool, lower Charge Air Temps, higher boost, and more fun! From this group of turbos the GTX2860 and GTX2863 are less commonly seen due to their lower top end performance compared to the GTX2867. We feel that the GTX2867 is the best match for our 2.0L EcoBoost as it is a responsive turbo which will produce a very broad (flat) torque curve and power up to 420WHP. Expect the GTX2867 to reach 20psi a little below 3000RPM in 4th gear.

GTX2867 powered Focus ST making 413WHP

2. ATP/Garrett GTX2971, GTX2976: Very similar to the GTX2867 but with more top end and a smidge more lag. These turbos feature a bigger 11-blade billet compressor wheel and slightly bigger turbine wheel. From these two turbos we recommend the GTX2971 as we feel the compressor/turbine are a very good match for each other. Expect spool to be 2-400 RPM later than the GTX2867 with power potential of 420-450WHP. Here are some photos comparing a GTX2867 and GTX2971. The difference in size is quite obvious.

3. ATP/Garrett GTX3071R / GTX3076R: A step up from the GTX2971/GTX2976 these turbos have bigger exhaust fans and thus slower spool and more top end. These turbos also have an 11-blade compressor wheel and ball bearing center cartridge for to help with spool and maintaining flow. These turbos will spool a couple of hundred RPM later than the GTX2971 and will produce more power right to redline. To get the most from one of the larger turbos it is recommended to build the block and run high boost with a high redline. For serious drag racing applications where spool is less important and you are looking for 475+ WHP we recommend one of these turbos and an aux fuel kit.

Wondering what is it you have to look forward to?

Thanks for reading, we hope it helps!

– The Stratified Team