Choosing The Right Turbocharger

    13 MAY 2024 - Jeff Willis

    For those of us with modded Subarus, or any turbocharged vehicle for that matter, long-term ownership means that at some point we must replace a worn or damaged turbocharger. The joy of driving these cars comes in many forms whether it be the looks, the sound, the handling, but for many of us, the thrill derives from the power a turbocharger makes when boost hits. The blow off valve noises, an aftermarket wastegate opening, the speed, all of these elements are highly addicting. However, all these exciting mechanical movements do come with a price, and more importantly a responsibility. The bigger you go, the harder it will be on your motor. How many motors are you prepared to replace?

    The aftermarket has so many turbocharger options that it will make your head spin. Now reputable brands such as Blouch Performance, COBB Tuning, and GrimmSpeed all specialize in Subaru and know the limits of Subaru engines. They know how to make a turbocharger that will work within the confines of the Subaru EJ or FA powerband. With any reputable turbocharger brand, you are going to pay the justified price for a quality product. The problem is, is that there are several replica brands out there for cheaper prices, but in the long run, they will cost you more money. If you are in need of a new turbo for your Subaru, you need to think about if you plan on making more power, or if you just want a direct replacement just to get you back on the road.

     

    THE ENGINE

    Objectively speaking, from a stock EJ or FA, you aren’t going to get away with 400 HP. Not for very long anyway. A conservative tune helps with all the fuel mods, along with the rest of the supporting upgrades. But you really need to think about other key factors such as, is your WRX your daily driver? What does your budget look like? And most importantly, how bad is your right foot. Yes, we all know someone of a someone who made 400 HP on their stock EJ and has driven it hundreds of thousands of miles or some exaggerated number. But always having a broken-down Subaru with costly repair bills really kills the overall ownership experience.

    Now on the other hand, if your engine is a closed-deck block with forged guts and a standalone engine management system and you have your tuner on speed dial, then you know what you’ve got yourself into. You know what it takes to maintain a Subaru at this level, and you know what it takes to be competitive at the drag strip or if you have a dedicated Time Attack race car.

    This is more for the everyday enthusiast who use their Subaru as a daily driver, and who needs to replace their turbocharger, but do it responsibly without getting sucked into the black hole of endless aftermarket options outside of the brands we know and trust.

     

    WHAT IS JB OR BB?

    For those of you new to the turbocharger world, you will see the abbreviated initials of JB and BB in the turbo title or description while shopping. JB stands for journal bearing, while BB stands for ball bearing. What is the difference between the two? Why is BB more expensive?

    The bearings to the left of this photo are journal bearings. The bearings to the right of the photo are ball bearings. Most turbochargers will be a journal bearing type. In a nutshell, inside the turbo is a shaft that connects both the compressor wheel, and the turbine wheel. The turbo spins at hundreds of thousands of revolutions when in use, and the turbo needs proper oil lubrication so that the bearings can keep the shaft spinning properly. Ball Bearing turbochargers are more complex as the ball bearings allow the shaft to spin faster, and/or easier. Ball bearing turbochargers depending on the size, can spool much sooner than a conventional journal bearing type, and they also have coolant feed and drain ports to go along with the oil fed and drain ports to help keep the temps down. This is why when many shop for turbochargers, they opt for the ball-bearing type due to the better performance, and the reduction in turbo lag.

     

     

     

    WHAT ABOUT BILLET WHEEL?

    Blouch Turbo TD05H-16GXT 7CM w/BILLET WHEEL 2002-2007 WRX / 2004-2021 STI

    Like stated in the example the example above, a billet compressor wheel will be more durable when compared to your standard compressor wheel. Micro debris such as dust or dirt particles, and even filter element can be digested by the turbocharger. A billet wheel is less prone to chipped blades. And this is especially important because as both the compressor and turbine wheel spin at hundreds and thousands of revolutions, and the key factor is shaft balance. If you have a chipped or damaged blade on the compressor side, it can throw off the balance at boost, causing the compressor wheel to eventually contact your compressor cover, and then you risk having a chewed-up compressor cover which you would need to replace the entire turbo.

     

    T3 OR T4? WHAT IS THAT?

    T-4 Turbine Housing

    When you research turbochargers and read “T4” or “T3” housing, this is a reference to the exhaust housing, aka turbine housing of the turbocharger. The housing bolts onto your exhaust manifold, or in Subaru’s case, the up-piper. The bigger the turbo, the bigger the exhaust housing will be to allow for more exhaust gas flow. Now for Subarus whether it be a WRX or STI, they have their own turbine housing design so for most turbochargers, you will never see a direct bolt-in T3 or T4 turbo for the Subaru because of this reason. The only time you will need a T3 or T4 turbo for a Subaru, is if you have a custom rotated turbo kit or an up-pipe that has a T3 or T4 flange. For the examples that SubiSpeed carries, the majority have been designed to be direct bolt-in units with the Subaru-specific 3-bolt exhaust housing flange shown below:

    STI Turbine Housing

     

    And for reference, here is a Turbosmart T4 turbocharger that would work well in a MKIV Supra, not so much in an STI unless you’re planning on making 1200+ HP:

    TURBOSMART TS-1 TURBOCHARGER 7675 T4 0.96 A/R

     

    WHAT TURBO SHOULD I GET?

    This depends on your power goals, and your power goals depend on a myriad of other things you must address. If you plan on making 400+ horsepower, you must build your motor with forged rods and pistons. If you are making 300+ horsepower, you need to have a tune, and the correct fuel mods to supplement your engine with the right amount of fuel so you don’t melt your pistons during boost. Now the majority of turbo upgrades that SubiSpeed carries are capable of making more power, torque, and boost that are also direct bolt-on units. You just have to make sure that you have a proper boost control solenoid with the boost turned down. Remember that a turbo that makes more power than the OEM unit flows more air. Therefore, an aftermarket turbo at 17 lbs. of boost will make substantially more power when compared to the OEM turbo tuned at 17 lbs. of boost.

     

    REMEMBER, IF YOU GET A BIGGER TURBO, YOU NEED THE SUPPORTING MODS

    As mentioned above, if you get a larger turbocharger, then you need to consider a few things. Since many are direct bolt-on replacements, this does not mean that the rest of the components will just bolt on, you need to think about the turbo inlet hose. But then be careful about the boost numbers. The most important mod you need to make sure you have with an upgraded turbo would be fuel mods. So, you need a higher-flowing fuel pump, larger injectors, and especially a larger intercooler. Because aftermarket turbochargers make more power, they will especially be more prone to heat soak through the factory top mount intercooler.

    Take a look at our turbo Install video to see some of the mods that work well with an upgraded turbo:

     

     

    IF YOU HAVEN’T BLOWN UP YOUR TURBO, MAXIMIZE THE POTENTIAL OF YOUR OEM TURBO

    That’s right. You can make between 330-350 HP through the stock turbo with supporting mods. Here is a list of mods you can look up to make more power, if your current turbocharger is still in good standing, and click on any of the examples to see what makes for great mods:

    • COBB Tuning V3 Accessport – The Accessport is hands-down the best handheld tuning device for the Subaru. COBB Tuning has many different downloadable MAPS you can choose to work with your current, or future mods.
    • Cat-Back Exhaust System – Always upgrade your exhaust from the back then moving forward to allow your exhaust gases to escape through the downpipe, and open into a free-flowing valley of larger piping with minimal bends. Plus, Subaru rumble noises too.
    • Catted Downpipe – Like all turbocharged vehicles, the EJ and FA love a good downpipe. Be aware though, a downpipe is not a mod you can just bolt-in and be on your way. Any aftermarket downpipe has larger piping that replaces the highly restrictive OEM unit. This means more power and boost than what your ECU will recognize. Therefore, you must get a tune – Good thing you’ve got that Accessport on your list.
    • Cold Air Intake – Along with a cat-back a proper cold air intake allows the turbocharger to inhale a larger volume of air much quicker than the restrictive OEM airbox. This reduces spool time and increases the throttle response. Depending on what you choose, a tune will be required sometimes due to the increase in horsepower.
    • Boost Control Solenoid – A GrimmSpeed unit for example works much faster than the OEM unit to increase the boost response while hitting those boost targets faster, and with more accuracy.
    • Fuel Pump – As boost increases, the power increases. This means that you will be hitting fuel cut. Make sure you have a Wideband O2 gauge to see where your AFRs stand at peak boost. If you are running lean, you need to stop boosting, and upgrade your fuel. A proper fuel pump pushes more fuel to your injectors to make sure they do not have any gaps due to the limitations of the OEM fuel pump.
    • Fuel Injectors – When you are pushing the limits of your OEM turbo, a larger fuel injector will be needed not only to handle the increased duty cycle, but to also flow E85. Your OEM injectors are designed to work with pump gas only.
    • Larger Intercooler – A larger top mount should suffice. A front mount is required over 400+ HP. You need a larger intercooler with an upgraded turbo because upgraded turbos flow more air, therefore it will compress a larger volume of air through the intercooler. The OEM STI and WRX units are small and are prone to heat soak. Heat soak is where the intercooler can no longer cool the intake charge temps, pushing warm air into the intake. You will not have the full potential of your other mods.
    • Blow Off Valve – When making more boost, you might out boost your factory BOV. This means that the internal BOV spring may be too soft to hold the boost. A quality aftermarket unit will have a stiffer spring to hold the boost while purging the pressure faster, but truth be told we like the noises too.

     

    TURBO EXAMPLES

    Ready to shop? Here are some chosen examples that are direct bolt-on units that are capable of making more power, but appropriate for most everyday Subarus:

     

    GRIMMSPEED CHASE JB400 TURBOCHARGER KIT – 2002-2004 STI / 2002-2007 WRX

     

    FORCED PERFORMANCE FP BLACK 84MM 8CM IWG w/OIL FEED LINE 02-07 WRX / 02-21 STI

     

     

    COBB TD05H-20G-8 2008-2021 STI