Category Archives: Tech

SteamSpeed STX 71R BB Prototype Tested: 470 WHP

Hey guys,

Sam here from SteamSpeed.  We super happy to get back to you with the results of our SteamSpeed STX 71R ball bearing turbo for FA20 applications, ie. the 2015+ WRX.  The basic specs are:

  • Stock frame meaning it just bolts up in place of the OEM turbo
  • Utilizes a Garrett GT ball bearing CHRA (center housing rotating assymbly) sourced from Garrett Japan
  • It is GTX2971R spec meaning the we make our own compressor wheel of that size, and reuse the Garrett GTX29 turbine wheel.

[STX 71R for FA20 Prototype Pre-Test Recap]

Several months ago, I wrote a longish article discussing challenges with the JB CHRA and how the new BB CHRA.  It is a great read, and I highly recommend that you read it, but it lays out why we think the BB version of the 71 will be a superior turbo to our JB version.  The next section outlines, the basic points.

[STX 71R for FA20 Performance Performance Hypothesis [Pre-Test]]

  • The OEM style twin scroll turbine housing is restrictive for turbos larger than the OEM unit and our STX 67 JB turbo.
  • This means for our big turbos, exhaust back pressure ratios can get well beyond 2:1 that is efficient for a JB CHRA.
  • If you are going 5:1 or 7:1 makes it hard to build power and it wears out the journal bearings and especially the thrust bearing.
  • Tuners that have a good strategy to manage this backpressure can make good power with the larger STX 67+ and 71 turbos, but if they didn’t, sometimes our customers would be disappointed.
  • The main point of that post was that a BB CHRA actually solves all of these problems:
    • The CHRA can stay efficient even if the pressure ratios are 5+:1
    • This means, it will be a lot easier for all tuners to build power with the BB version of our turbo.
    • The turbo will just make more power under the curve in general
    • The the thrust bearing is more durable, so the CHRA will stand up to more punishment.

[STX 71R for FA20 Test Results]

We set out to actually prove if the BB version of the STX 71 would perform as well as we had hypothesized, and solve the issues we had with the JB CHRA on the larger turbos.  The short version is that yes, the SteamSpeed STX 71R BB Turbo for FA20 did exactly what we thought it would.  It was a lot more efficient that the JB version of a similar size; therefore, it made more power everywhere.  I suspect that tuners all over will be having an easier time getting results their customers want.

Here is the dyno result.  470 whp on E50 and 410 on 91 octane pump gas, and not measured on this chart, a ton more response everywhere.  Note: this is at high altitude in Utah.

SteamSpeed STX 71R for FA20 Dyno Plot. Green – E50, Black – 91 pump gas

[Technical Notes From Jessie at FNP]

Jessie: “Hey, First let’s go over what we saw, liked and disliked with the unit.


It’s big, if the new unit has a clearance for the oil pan and obviously ships with hardware we are good.  Obviously as the prototype it is going to have clearance issues, and fitment issues.  There were literally no other issues noted from Luke on install.”

SteamSpeed: This will actually be a non-issue for retail units.  We have actually already resolved all fitment issues on our production 71R.  The production model has a modified turbine housing with a cutout to clear the OEM oil sump without modifying it.  We also designed and manufactured custom studs that we include with the 71R install kit.  This is how the retail unit will work:

Notice we modified the turbine housing to work with the OEM oil pan without modification. We also include custom studs with the install kit.
Notice we modified the turbine housing to work with the OEM oil pan without modification. We also include custom studs with the install kit.



Sounds epic.  Do yourself a favor a crack open the boost nipple when running.  The ball bearing turbo sounds incredibly mean at idle.  With a catless exhaust it should sound great out the tail pipe.  Think diesel turbo, screaming at idle.

Response, Response, Response.  This turbo is incredibly responsive compared to the previous version.  Transitions in and out of boost are much quicker.

More linear boost curve via WGDC input.  What do I mean?  Check out this boost profile compared to WGDC on the old vs new turbo.  The new unit is much MUCH more linear with interrupt cycle.  This tells us the effects of back-pressure are far less of an issue with this upgraded unit.  You can also see the old turbo have more “Creep” under the curve.  The new unit doesn’t not do this.  The compare for RPM isn’t valid, as the previous tests were done in 4th, the current in 3rd.



Makes more boost in the upper RPM’s.  This also is a direct causation from the upgraded cartridge.  It seems to be able to operate at higher levels of back-pressure with ease.

Red JB vs Yellow BB

Less oscillation of MRP than the outgoing cartridge.  Just one of those anecdotal observations, normally we see much greater fluctuations in boost on the FA20 with our incredibly fast sample rates.  This unit fluctuated much less, the average was 18% realized lower fluctuations.  This is a great indication of how much more air is being delivered.


Much more efficient flow from the turbo.  Check out the new vs old charge air temps!

New unit held much better boost.  From 1.9bar avg on the old unit at redline on 100% interrupt, to 2.3bar avg.

Output: Was increased by 12.35% over the older unit.  This was also impressive as the turbo could have easily generated around 8% additional output, but the owner of the test vehicle was very specific to “Take it easy”.  Based on the airflow averages and their changes, I’d say this observation is fairly precise.

Check out these airflow differences:  Old Turbo 229 average max, New over 300!  (it was 309 average when extrapolated up).  That is an increase of 35%.  Same intake, and injector scalings were used on both turbos.  Compared to the stock turbo this is over 56% increase in flow!

Well, hope this helps you guys.  I poured over all the data and these were the things that popped out at me.

Jesse @ FNP Tuned”

Installation Guide for EJ fitment Steam Speed Turbochargers.

We are proud to announce  a simple installation guide that can be used on all EJ fitment vehicle.  We kept most of the description as generic as possible and high lighted the key steps in replacing your turbo. As stated in the video there may be differences in your exact application.  Below the video is the full transcript of the narration.

Full Transcript

Welcome to the installation video for EJ fitment steam speed turbo chargers.

  • Today we will be installing a steam speed stx67r-10 twin scroll on our version 8 ej207. This process can be applied to any EJ fitment vehicle or to these listed part numbers.
















  • Notice our vehicle is far from stock and what you see in the video may not match your vehicle. However, the key points of the process will be the same.
  • We begin by gaining clear access to the turbo. We removed the air filter and Mass Air Flow sensor housing and charge pipe at the turbo.
  • If you have a top mount inter cooler remove that from the throttle body and compressor outlet.
  • The silicon or plastic hoses may be stuck. Use brake clean to break the adhesion and carefully work the sealing edge with a hose pick. Take caution not to puncture or tare the hoses as this will lead to a boost leak later.
  • Next remove any heat shielding you may have installed. Whether that’s a turbo blanket such as the steam speed titanium or carbon fiver turbo blankets or bolted on stamped steel heat shields.
  • Next use a rust penetrator such as “wd40”, or “pb blaster” and soak the turbine housing bolts on the up and down pipe flanges. Allow them to soak for at least 15 to 20 minutes.
  • While the bolts soak, place a collection pan underneath the vehicle directly below the turbo and remove the coolant and oil lines connected to the CHRA portion of the turbo.
  • I suggest using hose clamps to minimize the amount of spilled coolant and coolant unnecessarily draining from the engine.
  • I also cap the coolant lines on the turbo to also minimize the mess.
  • Next you can begin to loosen and remove all the up and down pipe flange bolts.
  • Caution, these bolts can break if too rusted together. If this happens you will need to replace them.
  • When the flange bolts and nuts are removed disconnect the down pipe from its solid mounts on the side of the transmission. Up plug any oxygen sensors and move the down pipe from the vehicle.
  • Once the down pipe is clear loosen the compressor inlet pipe and maneuver it toward the front of the vehicle underneath the intake manifold until it is clear of the compressor housing.
  • Then you should be able to lift the turbo off the up pipe flange and oil drain tube.
  • Take caution with the oil drain tube as the hoses can stick and tension clamps can lose their tension over time and fall off while removing. The open oil drain will be exposed and can risk material falling into it.
  • Place the new and old turbo chargers on a work bench and note any comparable differences that may cause fitment issue or parts that may need to be transferred such as coolant lines or the oil drain tube.
  • Next you will see there are 3 studs provided with your new turbo. Place these in the corresponding locations compared to your previously removed turbo. Then tighten these studs with a 7mm open end wrench.
  • Apply thread sealant or thread tape to the oil feed line fitting on the back side of the cylinder head. This will be a hard line on AVCS equipped engines.
  • Then install the oil feed line.
  • Prep the up and down pipe flanges for new gaskets, remove any surface rust or grease and oil with a fine grade abrasive pad. Then place your new up pipe gasket on the flange.
  • Place your new steam speed STX turbo charger on to your up pipe flange. Remain aware of the oil drain tube alignment. If the drain tube is new it may be more difficult to slide onto the metal portion connected to the CHRA (center housing rotation assembly). You can apply a thin film of engine oil to the rubber drain tube to ease its fitment on to the metal portion. Then Place the tension clamps back into place.
  • Carefully guide your turbo inlet pipe onto the inlet of the compressor housing. On larger turbo’s this may be more difficult as the compressor inlet diameter may be larger than the diameter of your inlet pipe. Tighten the clamp, securing it to the compressor housing.
  • Begin to reinstall all the nuts and bolts securing the turbo to the up pipe. Be sure all nuts and bolts are in place before tightening all the way. Place your down pipe gasket on to the outlet flange and studs on the turbine housing. And guide the down pipe into place.
  • Then install the down pipe flange nuts and bolts. Again do not tighten until all bolts are in place.
  • Torque all up and down pipe bolts to 26 ft/lbs
  • Next apply thread sealant or tread tape to the oil feed line fitting on the top side of the CHRA.
  • Reconnect the coolant hoses and vacuum lines.
  • Carefully check each step on the installation to be sure nothing was missed or any hoses moved out of place.
  • Reinstall the charge pipe and air filter housing.
  • The most important step is priming the oil system. If this step is not performed eruptible damage will be done to the CHRA.
  • Disable the ignition system but either removing the crank sensor signal.
  • Crank the vehicle over for a minimum of 30 seconds.
  • Re connect the ignition system and start the car.
  • Allow the vehicle to idle for 15 to 20 minutes and reach operating temp slowly. Do not rev the engine.
  • Inspect your work for coolant or oil leaks at the fittings and hoses.
  • Be observant for a hiss noise of possible vacuum or intake leaks.
  • Once the vehicle has been thoroughly checked, let it cool and reinstall your heat shielding.
  • It is now imperative your vehicle is tuned by a trusted tuner using a chassis dynamometer.


SteamSpeed FA20 Turbo Resutls

SteamSpeed STX 67 for 2015 WRX

Here is a good dyno result of a SteamSpeed STX 67 on pump gas done at Bren Tuning with a before and after, green being before, and red being after.  Obviously there are gains everywhere.  You can see their post on NASIOC here.  The short of it, the customer go a 85+ WHP and 70+ WTQ gain on pump gas!

SteamSpeed STX 67 for 2015+ WRX
SteamSpeed STX 67 for 2015+ WRX

Here is a standard STX 67 for 2015+ WRX tune at COBB Surgeline.  Unfortunately it does not have the before plot, but it was a 60 whp gain on pump gas.  This car had a 3″ turbo back, intake, and front mount intercooler.  It was tuned at COBB Surgeline.  We have to give these guys at COBB Surgeline props.  This customer was initially impacted by the wastegate flapper defect a few units had from the first production batch.  The guys at COBB took the time to correctly diagnose the wastegate problem.

SteamSpeed STX 67 for 2015+ WRX (pump gas)
SteamSpeed STX 67 for 2015+ WRX (pump gas)

SteamSpeed STX 67+ for 2015+ WRX

Here is a nice dyno plot comparing a fully modified 2015 WRX without the SteamSpeed turbo [green], then with the SteamSpeed STX 67+ [red].  This with some ethanol blend, around 50%.  This was tuned in Utah at FNP by Jessie.  It looks like about a 100+ WHP gain and 65 WTQ.

SteamSpeed STX 67+ for FA20 on Ethanol
SteamSpeed STX 67+ for FA20 on Ethanol

Steam Turbo Install Instructions

SteamSpeed Logo

Download the PDF – Steam STX Turbo Installation Instructions

Steam STX Turbo Installation Instructions

Steam STX Turbochargers are manufactured with the highest quality components, equipment, and procedures as possible.  When installed, maintained, and operated correctly, these turbos can provide many years of reliable service.  Incorrect turbo installation can lead to premature turbo failure and voids the warranty.  Professional installation is recommended.

Pre-installation Checklist

  • Make sure the engine, oil, and cooling systems are healthy, clean, and in good working order.
  • If you’ve had an engine or turbo failure, make sure the root cause has been identified and addressed.
  • Change the engine oil with clean new oil and a new filter.
  • Make sure the pre-turbo intake and pre-turbo exhaust systems are free of foreign objects.
  • We recommend replacing the OEM oil feed line, but if you are reusing the stock line, make sure it is clean and unobstructed. We sell upgraded stainless steel oil feed lines at affordable prices to help our customers avoid oil starvation problems caused by clogged oil feed lines.
  • Ensure the crank case ventilation system is operating correctly.

Turbo Installation
1. Remove the old turbo. If you are unsure how to do this, refer to the service manual for the car.  Generally this involves these steps:
– Remove the down pipe.
– Remove the connected intercooler and/or intercooler piping connected to the turbo.
– Disconnect and temporarily clamp the turbo’s water lines.
– Disconnect the oil feed line. Note: take care to not crack or over bend the stock oil feed line if you intend to reuse it.
– Disconnect the vacuum line from the compressor housing (if applicable).
– Unbolt and remove the turbo from the up pipe. The oil return hose and clamps will be reused.
2. Install the new Steam STX turbo. Perform the turbo removal steps in reverse.  Note:
– Make sure all of the hoses and fittings are tightly clamped post install.
– Always replace old gaskets with new SteamSpeed gaskets or OEM gaskets.
– Make sure all flange surfaces are flat and clean before replacing the gaskets.
– Pre-turbo exhaust leaks and post-turbo boost leaks are the main cause for slow turbo spool up.
– Replace corroded or otherwise damaged hardware as needed.
– Use OEM torque specs.
3. Prime the turbo by cranking the engine without firing for at least 30-60 seconds. You can disable the ignition by removing the ignition fuse, or disconnecting the sparkplugs.  Skipping this step will lead to premature turbo failure and will void your warranty.
4. Start the engine and let it idle for at least 3-4 minutes. While the engine is idling, check for leaks, and if any are detected, stop the engine at once and fix the leak.
5. Stop the engine and recheck the engine oil level.
6. Enjoy boosting with your new Steam STX turbocharger!

Supporting Modifications and Your Turbocharger’s Efficiency

Occasionally, we have the opportunity to help our customer troubleshoot situations where their expectations are not being met after installing one of our turbochargers.  This sounds bad initially, but hear me out.

For a moment, consider that a turbocharger is a lot like a big barrel of water.  At the top, there is an inlet where water can fill the barrel.  At the bottom there is an outlet where water can exit the barrel.  If the inlet at the top of the barrel is closed, it will be impossible to achieve constant, high volume flow out the exit.  Now consider the opposite, where the exit is barely open but the inlet is entirely open and a hose is pouring water in the opening.  It won’t take long before water is overflowing out the opening and there is still very little water coming out the exit.

Turbochargers work on similar principles, only more complex.   Their ability to flow is dependent on the engines ability to move the gasses that are injected into the cylinder for combustion.   For example, if one were to use our Steam STX 71 with a factory exhaust, it is likely that they would be disappointed on the dyno.  The factory exhaust is simply not capable of moving exhaust fast enough for the turbo to spool quickly or make power because the engine can only combust as fast as it can evacuate the exhaust gasses.  Therefore, the more gasses you can create, the more horsepower and torque you will make.  This process is contingent on the ability to move gasses through the system and out the tailpipes.

Sometimes when a customer might state that a turbo is spooling slower than expected, we discover later that there is an exhaust leak somewhere.   Since a turbocharger’s job is to leverage wasted heat from the engine by means of capturing it in the exhaust path, it makes sense that if that heat is leaking off before it reaches the turbo, the turbo will spool slower and produce less power overall.  This one takes us back to our early days in school where we learn about the Law of Conservation of Energy.

Another culprit of a let-down on the dyno can be the wastegate.  The wastegate is called that for a reason.  It’s sole purpose is to waste energy.  This is a good thing when it is tuned properly, and a very bad thing when it is not.  The wastegate’s job is to open when the turbocharger has pressurized the intake manifold to the proper pressure (usually measured in psi).  Let’s assume you are striving to reach 20psi with your tune.  When the turbocharger achieves this, the wastegate on the hotside of the turbo opens up to let exhaust gasses that would normally drive the turbine, escape around the turbine instead of passing through it.  This makes it possible for the turbo to flow at a desired rate without overboosting the engine.  If the wastegate is opening to early, or the spring is insufficient for the tune, exhaust gases that are necessary to make power will be lost along with the power they would have supplied to the engine.

Intercoolers.  We love them and we hate them.  We love them because they cool the air charge going to our engine, lowering the risk of detonation, and giving us much more power than we would have if they were hotter.   Hot intake gasses are less dense, and because of this, supply less oxygen per cubic liter than colder intake gasses.  A warmer intake charge also means that your tuner will have to compensate for those temperatures in power-robbing timing settings.   A good top-mount intercooler will be sufficient for most, however many opt for a front mount intercooler.  There are advantages and disadvantages to both.  Your build and your pocketbook will largely determine what works best for you.  A front mount intercooler means a lot more air is necessary to pressurize the intake system.  This results in power later, but it usually results in lower intake temperatures too.  Also, more piping, means more connections and more connections means more opportunity for leaks.  If you find that your intake is leaking, you’ll know it by a massive loss in power and it taking longer to reach boost.  The air that would have been used to combust a greater amount of fuel is being dumped to atmosphere.  That means less power to the wheels.

Supporting modifications influence your turbocharger’s efficiency.  The fewer you have, the less power you will make.  It is important to consider what other items will be necessary for you to achieve your goals when bolting on a device that is intended to push your vehicles power well beyond what the factory intended.

SteamSpeed TECH: How to Preload a Wastegate Actuator

How does one correctly preload a turbocharger’s waste actuator?

We get asked this question often, so here is a little guide on how to correctly preload a turbo’s wastegate actuator.  In general, you adjust the preload according to the pressure of the spring that is in the actuator.  Most aftermarket turbos are set to 1.0 bar.  Actuators can be adjusted up or down ~+/- 0.1 bar of their spring pressure.  Our turbos come preloaded with 0.9-1.2 bar depending on the application.

Our adjustable actuators can take a number of different springs to achieve a wide range of preloads.  We also sell them separately as a retrofit for people with stock or other brands of turbos.  Extra springs if you already have our actuator.

1. Attach the actuator to the compressor housing.

Attach the waste gate actuator to the compressor housing
Attach the waste gate actuator to the compressor housing

2. Attach the actuator to the arm of the turbine housing’s flapper arm.  Note: do not insert the cotter pin yet to the flapper arm.

Attach the waste gate actuator to the turbine housing
Attach the waste gate actuator to the turbine housing

3. Attach a boost source to the barb on the waste gate actuator.   Pictured below is a custom made apparatus that connects to an air compressor.  We also sometimes use a reversible vacuum pump (one that can be reversed to make pressure as well as vacuum) and use that to apply the target pressure.

Apply a boost source on the actuator's barb
Apply a boost source on the actuator’s barb

4. Apply the target pressure which should match the spring that is inside.  Then, apply 0.1 bar of pressure more than the target.

Add pressure to the target boost level
Add pressure to the target boost level

5. Check the flapper’s gap.  It should be open around 0.10mm at 0.1 bar beyond the target preload.  We are using a 0.10mm gap feeler to check.  If you do not have a gap checker, you can get close by watching the flapper to move ever so slightly.

Check the flapper's gap
Check the flapper’s gap

6. If the gap was correct in step 5, go to step 7.  If the gap is not correct, you fine tune by adjusting the actuator rod.  Shorten the rod to add more preolad.  Lengthen the rod to decrease the preolad.  Repeat steps 2-6 until the preload is correct.

Adjusting the length of the actuator arm
Adjusting the length of the actuator arm

7. Reattach the cotter pin.  You turbo is now correctly adjusted.

All finished
All finished



FAQ: Turbocharger Shaft Play

We often get asked questions about shaft play.  The concern is valid.  Before leaving the factory, all Steam STX turbochargers are inspected and validated to not have shaft movement beyond 0.09mm in any direction as part of our QA process.  Without precise measuring equipment, it would be hard for a person to detect that tiny amount of deflection.

Here is an example test where the max deviation was 0.027mm.

testing shaft play on a turbocharger
testing shaft play on a turbocharger

Typically shaft play implies bearing failure and damage.  Side to side movement implies damage to the main bearings.  In and out moment implies damage to the thrust bearing.  Once the shaft play is too extreme and the turbo’s wheels touch the housings, the whole turbo is ruined.

The most common reason to bearing failure is lack of lubrication, meaning not enough oil getting to the bearings, or the oil is old or contaminated such that it can’t protect the bearings.  Also, if a turbo is not primed before staring your car, the bearings will experience a sever lack of lubrication.  It will cause bearing damage and premature turbo failure.  FYI: The stand procedure is to crank your engine for at least 30 sec without starting it to get the oil throughout the turbo CHRA.

Poor lubrication is the 90%+ failure case.  Upon disassemble of the CHRA, it is very easy for us to detect oil related failures.

Oil Starvation
Oil Starvation

The other failures are due to customers just pushing their turbos hard.  Pushing your engine components hard isn’t a problem; you just need to be aware, it makes them wear out faster.  If you push your turbo to very high shaft speeds for long periods of time, it won’t last as long.  Turbochargers are normally balanced on a VSR (vibration sort rig) up to 100,000 RPM; however, pushing a turbo to high pressure ratios will exceed 100k shaft speeds.   Customers may run at higher pressure ratios, just like they can also have a 12k RPM readline, but it does impact durability.

Warning: engineering content:  Also, the rotating assembly will have natural harmonic frequency as elastic systems do.  The force on the turbine will also add additional vibrations at different harmonics depending on the design of the aero.  Basically the natural harmonics + forced vibrations can also damage the bearings.  Most of this is mitigated though, by the design of the turbine aero, and using the VSR to remove extra vibrations due to imbalance.  In other words, this type of failure can be avoided before you get your turbo through proper design and manufacturing.

Compressor surge can be destroy bearings as well, but can generally be avoided by designing your turbo system correctly.  If you don’t actually want to figure it out, the I would recommend getting some good advice on what you need.  Ask your tuner, or give us a call if in doubt.

For journal bearing turbos, damaged bearings are easy to replace assuming the wheels have not touched the housings.  It is possible for a normal person to replace them in their home garage if they are careful.  We however, resubmit the turbo through our entire QA process including a re-balance on a VSR.

Garrett ball bearing turbos are more resilient to abuse, but when they break, they are very hard to repair, well at least for any one other than Garrett.  Essentially they are designed such that the whole bearing assembly has to be replaced.  Garret does not sell then to the public.  The ones you see on ebay are fakes, FYI.

To recap, you can avoid most turbo failures by: following correct turbo install procedures, providing a sufficient and clean oil supply, and having the car properly tuned.  If followed, your turbo will last for years reliably.

Steam STX 71 Flow Testing [part 2] STX 71 vs GTX3071R

We have been able to compile our initial flow testing on our Steam STX 71 turbocharger, and we have to admit, our expectations have been exceeded.  We didn’t expect the STX 71 design to out flow the Garrett GTX3071R, but that is just what happened.  It turns out the original STX 71 design was actually quite good from the get go.  Don’t worry.  This testing is just a baseline.  We intend to make it even better.

Learn more about the Steam STX 71 Turbocharger here.

Just as a refresher, this is what the compressor map lines mean.

Compressor Maps Explained

Here is the Steam STX 71’s compressor map.  As yo can see, it has a max flow of a whopping 59.5 lbs/min.

Steam STX 71 Turbocharger Compressor Map
Steam STX 71 Turbocharger Compressor Map

How does the Steam STX 71 compare to the Garrett GTX3071R? See for your self. The STX 71 actually out flows the GTX3071R by at least a few lbs/min.

Steam STX 71 vs Garrett GTX3071R compressor map
Steam STX 71 vs Garrett GTX3071R compressor map

Here is the turbine section map for our Steam STX 71 turbocharger in our version Subaru WRX STI single scroll turbine housing.  It is mildly ported and 8 cm^2 in Mitsubishi speak or 0.55 A/R in Garrett speak.  The both measure the “size” of the scroll.  Bigger means the housing can flow more generally speaking.

Steam STX 71 turbine map
Steam STX 71 turbine map

How does our Subaru turbine housing flow compared to the Garrett T3 housing for a GT30 turbo?  It actually flows quite well for being “smaller” than a 0.63 A/R T3 housing.  We attribute this to our signature 9-blade high flow turbine design.

STX 71 vs GTX30 turbine map
STX 71 vs GTX30 turbine map

Steam STX 71 Flow Testing [part 1]

Steam STX 71 turbo mounted to gas bench
A Steam STX 71 Turbo mounted to the gas bench test rig.

Did you ever want to know how it’s possible for our Steam STX 71 turbocharger to make over 425+ WHP on your STI?  It’s all about flow dynamics.   We are not content with just having high-quality high-performance products so we decided to take the engineering to the next level.

Learn more about the Steam STX 71 for USDM STI, or JDM twinscroll STI.

Here is a dyno plot of our Steam STX 71 turbo in action.  There is a whopping 140 WHP gain over the stock VF39 turbo with very little left on the table.

The STX 71 vs VF39
The STX 71 vs VF39

Other manufacturers, like Blouch and ForcedPerformance, can simply make claims to how much their products flow.  But, how do they arrive at that number?  Without compressor maps to demonstrate thorough testing, one can assume they are just guesstimating.  Why make a guess?  Because real engineering is expensive.  Turbo testing is also very expensive, but that is what the big boys do to actually improve their products.  You can’t get, what you don’t measure.

Garrett also makes claims to how much their turbos flow, but they actually provide detailed compressor maps.  This is the result of rigorous engineering efforts.

Compressor Maps Explained

When Garrett improved their ball bearing turbo line, they actually provided empirical data showing how their product has improved.

gt4202R vs gtx4202r compressor map
gt4202R vs gtx4202r compressor map

Although we have had great results with our STX 71 model, and lots of happy customers, we never stop thinking our products can be better.  How do you make a great design better?

Steam STX 71 Performance Testing

First step, measure the performance of the current design.  The way Garrett and other serious turbo companies make compressor maps is by testing it on a gas bench, so that is exactly what we are doing.  The gas bench provides a super controlled environment to reliably test the turbocharger.

We measure a number of things on the gas bench: compressor wheel speed, pressures and temperatures before and after both housings, etc.  With this data, we will be able to generate compressor maps similar to those of Garrett.

Checkout our current production STX 71 on a gas bench as we map out the performance and efficiency of the current design.

Here is a production turbo with the turbine housing all mounted up to the hot side of the gas bench.  The yellow thing sticking out of the compressor housing is a speed sensor.  It measure how fast the compressor wheel is spinning.  The compressor wheel can spin in excesses of 150k RPM.

Steam STX 71 turbo mounted to gas bench
A Steam STX 71 Turbo mounted to the gas bench test rig.

Oil anyone?

Steam STX 71 turbo mounted to gas bench
Here the center housing’s oil ports are hooked up to ensure proper lubrication and cooling.

Here is the cold side being hooked up.

Steam STX 71 turbo mounted to gas bench
Here is the cold side getting hooked up.

Troubleshooting Slow Turbo Spool

When our customers experience slow turbo spool, we take it personally.   We want our customers to have a great experience with our turbos.  There are a few things that are absolute musts before you get your car tuned if you expect a good tune result.

Vehicle preparation:

  1. Ensure you have the minimum set of modifications
    • 3″ high flowing turbo back exhaust
    • upgraded fuel injectors and pump
    • upgraded intercooler (recommended)
    • big MAF intake (if your tune is not speed density)
  2. Have a healthy motor
  3. Ensure there are no leaks
    • in the intake
    • in the exhaust pre-turbo

#1 is really about hitting your best possible numbers.  #2 is more about the longevity of your build.  #3 will really kill the spool and responsiveness of the turbo.

Here is a representative result of what we would expect to see of a STX 71 on a built EJ257 (AVCS not working).  This car had all of the required supporting mods.  Versus the stock STI turbo, the VF39, there is hardly any trade off in terms of power and torque, and a something like 130 WHP in upside, and power until redline.

STX 71 vs VF39 turbo

In this particular case, the turbo and accessories were later upgraded to an even larger front mount intercooler, external wastegate, and our production Steam STX 71 turbo.  Improving items from #1 did indeed improve the peak HP by around 30 whp, but the owner was understandably concerned about how late the power came on.

Proto STX 71 vs Prod STX 71 (exhaust leak)

The most reasonable explanation for the huge amount of lag, is #3, or in other words, an intake leak, or a pre-turbo exhaust leak.

As a the turbocharger is the heart of the power, and a decent investment cost-wise, it is easy to point the finger at the turbo when power delivery is not within expectations.  After expressing concern that the turbo could be the cause for the late spool, the owner eventually checked for leaks and found this, a huge up-pipe exhaust leak.  An up-pipe leak is perhaps one of the most common leaks for Subaru turbochargers.  This has a lot to do with the flange design.  Notice that the leak is out the weakest side of the flange, the side with the largest distance between studs.   For this reason, we encourage customers to triple check the installation to be sure that they do not have leaks if they are experiencing lag.   It’s a common initial response to not want to check for leaks; however, going in in for a tune with a leaking turbo system will be disappointing.  We’ve had tuners tell us how common this scenario is.  Based on their feedback, it is our recommendation to check every new installation for leaks before going in for a tune.


The moral of the story is that, we want you to have great results with your turbo, but leaks and insufficient supporting mods both have the ability to decrease any turbocharger’s efficiency and output.  Nobody wants that.

If the turbocharger isn’t making the power you would have hoped, check to see if their are some gaps in the supporting mods.

If you are experiencing delayed boost, for example, 5000+ RPM peak torque on a STX 67 or 71, check for exhaust leaks, and pressure test the intake.