World One Performance Blog

All right, so you’ve got the full exhaust, you may or may not have an intake, and you’ve got some engine management that we mentioned in the previous blog entry, so what’s next? Before we actually dive into talking about replacing that snail under the hood, it’s important to mention the pipe that leads to the turbo itself from the headers. This is the uppipe, and for the 02-05 WRX, it is home to the third catalytic converter in the exhaust system. Due to this cat being there, it is important to replace this pipe whether or not you decide to go with an aftermarket turbo or not. There’s been more than a few cases of the high temperatures of the turbo heating up the material that makes up the catalytic converter, which then breaks apart and has nowhere else to go but into your turbo. Since the uppipe replacement is probably the most difficult and time-intensive exhaust part to replace, it’s wise to either do this or have it done when you replace your downpipe, and of course when you replace your turbo. Given the difficulty and time needed to do this replacement, we don’t normally recommend replacing an already catless uppipe in the STI or the 06+ WRX for example since the smoother exhaust flow of an aftermarket uppipe is usually negated by the cost and time required for replacement.

So now that you’re not putting your turbo in danger, let’s talk about your stock turbo itself. I’m going to try my best not to get hung up on names and specs, so please bear with me. The 02-07 WRX and Forester XT come stock from the factory with a Mitsubishi TD04L-13T turbo. For the 08 WRX, they changed this turbo to a Mitsubishi TD04-13T to match the new style intercooler from the Legacy GT, but then Subaru decided to change it again to the IHI VF52 for the 2009 and up since the 08 WRX was critiqued as not having enough punch. The 04-06 STI use an IHI VF39 turbo, while the 07 STI uses an IHI VF43 turbo, which is essentially a slightly modified VF39. By contrast, the newer 08+ STI uses an IHI VF48 turbo that is completely different. The 05-07 Legacy GT comes stock with an IHI VF40 turbo, but that has since changed to the IHI VF46 turbo for 08 and up. It’s most likely that the newer 08 and up Forester XT also uses this same turbo, but we haven’t had any at our shop yet to verify.

Now, I know I’ve mentioned a plethora of letters and numbers that probably don’t mean anything to you at this point, but the main point out of all this is the pure and simple fact that choosing an aftermarket turbo for your car is no easy, quick and dry process. The reason why Subaru has gone to different lengths to use such different turbos in each model and model year is to provide a driving experience that is responsive, quick, and satisfying. If Subaru just wanted to go balls out with the power, they could’ve easily slapped on a larger turbo for more high-end kick, at the expense of low-end response. Mitsubishi did this with their FQ-series Evos and while they were fast on the top end, just about every automotive journalist could make a sandwich by the time the car hit boost. In choosing the right turbo for your needs, being able to make a sandwich before boost is probably something you’ll want to avoid for the vast majority of the people out there. Thus, it’s important to set goals for yourself, do your research, and if possible, go for a ride in a fellow Subaru owner’s car so you can actually feel how a certain turbo affects the car’s drivability.

We’re lucky at this point in time because there’s a wide variety of turbo upgrades available for Subarus to match just about every person’s needs, from upgrades for daily drivers all the way to full-on drag racing turbos. This wasn’t always the case however, and there was a time early in the age of the 02-03 WRXs that it was almost unfathomable that a WRX could run a quarter-mile in the 10s, much less the 12s. Back in 2002, just about every turbo upgrade consisted of a take-off turbo from a Japanese-model STI (since there was no STI in the US until 2004). These turbos were all IHI turbos, and ranged anywhere from the VF29 from the Version 6 STI to the VF34 from the Version 7 STI Spec-C. While these turbos were definitely larger than the stock WRX turbo and provided a very good and responsive upgrade, they lacked top-end power. Larger and older IHI turbos such as the VF23 and VF22 added some extra oomph, but even the modified versions of these such as the Power Enterprises PE1818 and PE1820 (respectively) would push a WRX into the 310 whp range with an aggressive tune. However, since these turbos came off of different models of WRX or STI in Japan, they were a direct bolt-on fitment, which still to this day is a big plus. Thus, combined with the limited engine management options at the time, the IHI VF-series turbos and their modified variants were pretty much the only upgrades available in the early years of the WRX in the United States.

Soon though, turbo manufacturers and modifiers started to experiment with different housings and brands. Both HKS and Greddy offered some of their own turbo upgrades, but they tended to be cost-prohibitive at the time, thus they were a rare find. Nonetheless, Greddy’s bolt-on turbo upgrade was their version of a Mitsubishi TD05-18G, and it’s possible that their use of this turbo style drew the attention of US turbocharger companies such as Forced Performance. In late 2003 and early 2004, Forced Performance (FP) began experimenting with taking Mitsubishi turbos and modifying them with housings so that they could easily bolt on to the WRX’s intake and exhaust paths. They would use different housings, different turbine compressor sizes, different sized compressor wheels, clipping the fins to supposedly help with spool, and even polishing and porting to help with airflow. After many experiments, FP ended up with a TD05-16G and a TD05-18G that bolted right into place, yet carried equal or greater punch than the IHI VF30 or VF34, which were the go-to turbo upgrades at the time. FP touted its 16G as being able to give as much power as a VF34, yet spool faster and in the end be cheaper to purchase. Their 18G consequently touted as the new big turbo upgrade for a WRX, capable of producing numbers in the 320 whp range with the right combination of parts, build options, and race fuel. The first models came out as being oil-cooled only, so turbo timers had to be used for proper cool-down after driving, but eventually FP added the stock water lines as well, making them just about as good a turbo swap as the IHI turbos.

While the new FP turbos gained popularity, the advent of the 2004 STI brought a new IHI turbo into the mix: the VF39. Similar in size and power potential to the VF29, the VF39 was often seen as a good upgrade for the pure and simple fact that you could buy one used for quite cheap. However, where would the new STI owners go for an upgraded turbo? The 18G was a possibility, but it wasn’t a huge leap in power over the stock VF39 thanks to the extra 1/2 liter of displacement. FP started to produce a few 20G variants, both with a TD05 or a larger TD06 housing, but STI owners wanted more. During the time that FP was experimenting with WRX upgrade options, they took one of their DSM upgrades, the FP Green, and modified it to fit a WRX. The FP Green is essentially a TD06-20G turbo with a larger compressor wheel, but this large size ended up being just a little too big for the 2.0L WRX and produced quite a bit of turbo lag. On the other hand, the FP Green seemed to be a perfect match for the new 2004 STI, and soon the Green became the go-to turbo for the STI. The 2004 World One STI used an FP Green with the then prototype Element Tuning Hydra EMS, which propelled the car to 440 whp on race gas and resulted in a 2nd Place Class Finish at the first Primedia Time Attack in November 2004. The FP Green was a good upgrade since there wasn’t much turbo lag and it had a decent amount of punch.

Nevertheless, STI owners still wanted more power. FP released their Red turbo, was had an even larger compressor wheel than the Green, but required a 3-inch turbo inlet tube for installation. Not satisfied with the stock-location bolt-on turbos, the demand grew for larger turbos that required the fabrication of special piping, since these turbos were simply too large to directly bolt on to the stock location and oil/water lines. Since turbos were going to be bigger, many companies started to release pre-fabricated kits using Garrett GT-series ball-bearing turbos. The theory behind the ball bearings was that they would help the turbo spool faster, especially given the much larger size compared to stock. These new “rotated mount” turbo kits typically utilized a Garrett GT30R or a GT35R, with the GT35R capable of well over 450 whp with the proper supporting mods. For those going for real big power, the Garrett GT40R and GT42R turbos were available for use with these rotated mount kits, sacrificing spool for big top end power and sub-10 second quarter mile times. Other companies such as Element Tuning also released rotated mount turbos to compete in this arena with faster spool but equal power numbers to the GT35R, but by in large the Garrett turbos were still definitely the most widely used. Although these new rotated mount turbo kits produced great power numbers, they did have a few drawbacks. First and foremost was the cost of these kits. Since new piping had to be purchased which often consisted of a new intake, downpipe and uppipe, along with an external wastegate, everything just added up to becoming quite expensive. Moreover, since the turbo was now rotated, a front-mount intercooler was an absolute requirement, so those people who wanted to retain the top-mount intercooler in exchange for a few less horses were completely out of luck.

Of course, the whole problem with the stock location turbos at the time was the simple fact that they couldn’t be large enough to produce the same power that the rotated mount turbos did, even if they spooled faster. Element Tuning helped solve this problem with their GT52 turbo, which provided the power of a rotated mount GT30R, but also spooled faster. On top of this, since it’s a direct bolt-on turbo, no extra piping needs to be purchased. This differed from the FP Red which produced similar power and spool, but required the 3-inch turbo inlet tube. Eventually, more turbo manufacturers followed suit to compete. Element Tuning then released the direct bolt-on version of the GT65 turbo, which is able to produce GT35R power in a bolt-on configuration, although requiring a 3-inch turbo inlet like the FP Red. ATP soon came out with their own direct bolt-on GT35R turbo, and for awhile, turbo technologies remained a bit stagnant.

Earlier in 2009, Forced Performance came back into the fray with their new HTA-series of turbochargers. Through their R&D processes, they were able to improve both the spool speed and also the power potential of their already venerable 16G, Green, and GT35R. For example, the HTA 68 kept the fast spool of the 16G, but put out power levels equal or greater than that of the 18G. Here at our shop, we’ve already seen great success with the HTA GT35R, as seen in our customer Luke’s 649 whp 05 STI.

So there you have it: the history of turbo upgrades for your Subaru. So which of these is going to work best for you? The most important thing to keep in mind is that generally speaking, the bigger you go, the slower the turbo will spool, but the more top end power you’ll have. It’s also important to remember that the same boost level for one turbo is going to put out a different amount of power than another turbo. By this, I mean that 18 psi on an STI’s stock VF39 is going to produce less power than 18 psi on a FP Green on the same vehicle. Remember, boost is all about the amount of air going into your motor, so with a bigger turbo, you thus are forcing in more air, and if you have more air at the same amount of boost, the pressure is much stronger, which of course leads to more power. To sum it all up, here’s a general listing of some of the turbos I’ve discussed here and their potential power levels (given the proper supporting mods and fuel):

For 2.0L WRX

• Mitsubishi TD04-16G: 210-230 whp
• IHI VF29 and VF39: 250-270 whp
• IHI VF30 and VF34: 260-280 whp
• TD05-18G and Forced Performance HTA 68: 280-320 whp
• TD05-20G: 290-330 whp
• Forced Performance Green and Element Tuning GT49: 300-350 whp
• Forced Performance Red, Forced Performance HTA Green, Element Tuning GT52, and Garrett GT30R (rotated and bolt-on): 350-400 whp

For 2.5L WRX, STI, LGT, and FXT

• IHI VF39: 280-300 whp
• TD05-18G: 300-340 whp
• TD06-20G: 330-370 whp
• Forced Performance Green and Element Tuning GT49: 350-470 whp
• Forced Performance Red, Forced Performance HTA Green, Element Tuning GT52, and Garrett GT30R (rotated and bolt-on): 375-500 whp
• Garrett GT35R (rotated and bolt-on), and Element Tuning GT65: 400-530 whp
• Forced Performance HTA GT35R: 550-700 whp
• Garrett GT40 and GT42R: 700+ whp

That should do it for this blog. In the next blog, we’ll talk about the supporting mods necessary to support the turbos I’ve talked about above, including having to build the motor to support these power levels. This will ultimately end the series, since we’ll no longer be talking about basics. As always, if you have any questions at this point, please don’t hesitate to contact us!

Hopefully, our previous engine management discussion didn’t overload your brain and just kept you coming back for more with this latest installment.  We pick up where we left off moving to the “Stage 3,” which typically involves an upgraded intercooler.  Just like with almost every modification we’ve discussed thus far, intercoolers carry with them some myths that many people believe to be true without ever having any personal experience to back up their claims.  But, before we get into those myths, it’s important to know what exactly the intercooler does in the first place.

The intercooler is essential to making power and maintaining efficiency on a turbocharged motor. There are two main types of intercooler:  air-to-air and air-to-water.  Most factory turbocharged cars use an air-to-air intercooler, since it’s much less complicated mechanically (no need for a water reservoir for heat exchange), not as heavy, and typically not as expensive either.  Air-to-air isn’t quite as efficient as a good air-to-water intercooler, but the cost/benefit involved tends to make the air-to-air intercooler the top choice is most situations.  Nevertheless, both types of intercoolers do the same thing:  they cool down the charged (compressed) air from the turbo so that it’s more dense when going into the motor.  As air is compressed, it generates heat, and heat also expands.  With more heat involved, there are less oxygen molecules, and with less oxygen going into your motor, the less power you can make.  The intercooler helps this by pushing this heated air to the intercooler core, which looks and acts similarly to a radiator.  As cool air passes over the intercooler fins, it helps cool down this air and makes it more dense as it then gets pushed into the motor.  Cooler, dense air contains more oxygen molecules, and thus you’re able to make more power.

Since the intercooler core acts as a heat exchanger, the size of the core determines how well or efficiently it can cool down the compressed air. The location of the intercooler core also matters as well, since it can easily be affected by ambient temperatures and needs proper airflow to do its job.  This is where a lot of the debate and myths start to come into play.  Subarus come stock with a top-mount intercooler (TMIC).  The size of this TMIC depends on the model and year of your car, with the STI TMICs typically being the largest offered from Subaru.  Given the size of the stock turbo (depending on the vehicle), the stock TMIC is usually perfectly fine for cooling and efficiency.  You can put on a larger intercooler and it won’t hurt anything, but you will need to get tuned properly for it and in the end, it might not yield much of a significant difference over stock.  Seeing gains of maybe 10 whp maximum typically isn’t worth the $900+ you’d have to pay to reach that much of a boost in power.

The location of the intercooler is the next matter of contention.  While the stock intercooler is located on top of the motor (hence the name top-mount intercooler), it really isn’t the most efficient place for the intercooler, especially when upgrading to a larger one.  The main reason for this is the simple fact that it sits not just on top of the motor, but also on top of the turbo, which of course radiates quite a bit of heat.  While the stock heatshield helps with this, when upgrading to a larger turbo, you can’t reuse the stock heatshield (or really any other heatshield for that matter) and thus the TMIC suffers greatly from heatsoak.  This is much more apparent when the car is stagnant such as in stop-and-go traffic or in line at the drag strip, rather than when the car is actually traveling at speed on the road.  In the case of the car actually moving, the stock hood scoop, combined with the stock air splitter, actually does a good job of helping provide proper airflow to the TMIC as well as shielding it from the ambient heat from the motor.  However, the problem then is with a larger TMIC, because the stock air splitter is not typically compatible with a larger TMIC, and in the case of an aftermarket hood, there simply isn’t any air splitter whatsoever.  This isn’t to say that a larger TMIC won’t do a better job than the stock one, but simply that there are definitely drawbacks to keeping the intercooler on top of the motor.

By far the best location for the intercooler is at the front of the vehicle.  Front-mount intercoolers (FMICs) draw air directly from the front of the car, which helps not just when the car is moving with air flowing over it, but also at a stop since it has direct contact with the outside air.  However, some people have insisted that by putting the intercooler at the front of the vehicle, there’s too much of a drop in pressure because of the added piping, and thus you will suffer additional turbo lag.  With proper tuning, this is completely false, and is normally a complaint from people who install a FMIC and do not get properly tuned or even tuned at all.  Owning two Subarus, both with FMICs, I can say with full confidence that there’s no difference in turbo lag whatsoever thanks to proper tuning.  However, there is indeed a pressure drop nonetheless, and thus it’s important to choose the right size core.

There’s always been the idea that bigger equals better, but when it comes to intercoolers, this isn’t necessarily always the case.  With Subarus specifically, there are some intercoolers that are just too large for the turbo its supporting, which causes too much of a pressure drop and thus a car isn’t able to make as much power as it could have with a smaller intercooler.  For example, the APS DR725 you see to the left here on Bailey’s car is gigantic, so it really wouldn’t be the right choice for a smaller upgraded turbo such as an 18G or 20G, and definitely a bad choice for the stock turbo.  Plus, given the fact that smaller intercooler cores such as the APS DR525, TurboXS, and Perrin are more than capable of handling well over 600 whp, you pretty much have to get a matching gigantic turbo to take full advantage of the DR725′s size.  Along with the size of the intercooler core comes the change in weight distribution, since you’re essentially adding 35 or more pounds to the front of the car.  Many would argue that this alone is reason enough to keep the intercooler in the top mount location, but generally speaking, this is more of a problem for those who do lower-speed racing such as auto-x, rather than types of racing that require the full power output, such as time attack and drag racing.  Finally, the other problem with a FMIC is purely aesthetic, since in most cases you have to do quite a bit of cutting of your front bumper cover to fit the intercooler there, not to mention you lose your factory bumper beam as well.  Most kits will include a replacement bumper beam of some sort, but it’s still not the factory, government-approved, and crash-tested bumper beam, so more frontal damage than expected is likely to occur should you get into some sort of accident.

Despite its drawbacks, we normally recommend FMICs to anyone who wants to bring out the full potential of the car.  It’s just important to choose the right size and design to suit your needs.  Of course, since a bigger intercooler doesn’t really benefit you without a bigger turbo, we’ll be talking about the different aftermarket turbos out there in our next blog entry.

With many turbo choices out there, Subaru owners are fortunate to have such a wide variety of sizes and power ratings available to them. However, with so many different names and numbers flying around, it’s easy to be confused as to what turbo works best. In the near future, we’ll have a post on choosing the best turbo to suit your needs, but this time around we’d like to highlight our best-selling turbo for 04+ STI owners: the Element Tuning GT52.

Unlike many other turbos out there that start relatively inexpensive, and then allow you to do your own customization in terms of housings, compressor wheels, porting, and polishing, Phil over at Element Tuning decided to do away with all the guesswork and actually create a turbo design that maximizes all possible potential given its size. Months of research and development went into the ultimate design of the GT52 turbo (as well as its smaller sister, the GT49 turbo). The final product ended up becoming our best-selling turbo, with countless happy customers both nationwide and internationally. Here’s how Phil himself describes the GT52 turbo:

This turbocharger is very similar to many other 7cm TD06 20G framed bolt-ons but that’s where the comparison ends. In this particular turbocharger we use a Garret GT30R 52 lbs compressor wheel, Garrett turbine wheel and shaft. The compressor is a GT30R rated at 52 lbs utilizing an internal wastegate.

Typically we see 20 psi by 3600-3800 rpm tuning with the Hydra with pump gas power in the 375-400 whp range. Both housings are completely ported for increased flow and wastegate performance. Race gas power is in the 475-500whp range.
Expect to achieve full boost with the proper modifications and a quality tune between 3500-4000rpms. Fuel upgrades for this turbocharger and proper engine management are required.

The Element GT52 has been recently updated to increase internal wastegate performance. Increased port work, larger wastegate port, and a larger wastegate valve has been utilized to ensure boost creep free performance.

Element GT bolt-on turbochargers include extensive porting of the turbine housing inlet, outlet, and wastegate passages. The wastegate passage is also enlarged and the turbine wheel modified to improve internal wastegate performance and creep free running.

All Element GT bolt on turbochargers are water cooled and come complete with water lines and an OEM oil drain line so installation is a direct bolt-on.

In our personal experience, we have been able to confirm all of Phil’s advertised numbers. This turbo does indeed hit about 20 psi by 3600 rpm and Patrick’s 07 STI hit 475 whp on race gas, which is well within the range that Phil described for horsepower numbers. Thanks to this turbo’s consistency and good availability, the GT52 has become our go-to turbo for any STI owner who wants a good balance of street power and track dominance. Since this turbo is a direct bolt-on, no extra piping or modification is required, although we do recommend replacing the turbo inlet pipe and switching to a Big MAF style intake. We also recommend Element Tuning’s stainless steel oil feed line for best results and to keep the turbo healthy.

You can purchase the Element Tuning GT52 Turbo for $1899 including shipping by clicking here.

Patrick’s been a great customer of ours for over a year now. After accumulating all the parts for his build, he sent is car to us for some major installations. The car arrived as a bone stock STI and underwent a complete transformation at our shop. Here are some photos of the build-up:

[View with PicLens]

ENGINE:
- Zerosports thermostat
- Moroso oil pan
- wideband o2 sensor for HYDRA
- APS fuel rails
- Element Tuning GT52
- APS DR725 FMIC
- Deatschwerks 1150cc injectors
- Tomei UEL headers
- Tomei UP w/ EWG
- Turbosmart EWG 38mm
- Samco turbo inlet
- APS 70mm CAI
- TGV deletes
- Element Tuning catch can
- Koyo radiator
- Perrin radiator hoses
- Invidia DP w/ EWG plumbed
- Cobb catback
- Turbosmart E-boost (sleeper series)
- 2.6 HYDRA
- HYDRAMIST
- Tial 50mm ‘Q’ BOV
- Walbro 255lph in-tank pump
- 1 step colder spark plugs
- Cover performance surge tank
- Bosch 044 external fuel pump
- Setrab oil cooler / thermostat
- P&L emissions block off plate
- P&L AVCS SS line
- Spec C tank for meth
- Element Tuning SS turbo oil feed line
- Turbosmart 1200 fuel pressure regulator
- Cosworth oil pump
- CP .5mm overbore pistons
- CP ring set
- Cosworth high performance rod bearing
- Cosworth high performance main bearing
- Kartboy exhaust hangers

SUSPENSION & MOUNTS:
- Race Comp Engineering Tarmac 2′s (5k,4k)
- Vorshlag camber plates
- WL big bar up front
- WL 26mm RSB
- Kartboy endlinks
- WL ALK
- WL BJE kit
- WL subframe lock bolts
- Cusco front strut bar
- Covert Performance subframe
- Covert Performance undertray
- Carlab’s X-brace
- TiC fender cowl braces
- P&L SS power steering line
- Cusco engine/tranny mount
- Kartboy solid engine pitch mount

BRAKES:
- Stoptech 4 piston 355mm front BBK
- rear Stoptech rotors
- Stoptech SS lines
- Ferodo ds2500′s
- ATE superblue brake fluid

TRANNY/DRIVELINE:
- ACT 6-puck unsprung (major PITA but I love it)
- ACT flywheel
- TiC tranny crossmember bushings
- TiC super shifter set (kartboy short shifter with bushings)
- TiC rear diff mount bushings
- Kartboy rear subframe outrigger bushings
- ACPT CF driveshaft
- SS clutch line

WHEELS/TIRES:
- 18 x 9.5 Enkei NT03+M +40 offset
- 265 Falken AZENIS
- Work lug nuts

EXTERIOR:
- v-limited lip
- Seibon cf trunk
- Ks-tech hood scoop delete
- wrx skirts
- Hella horns
- Nukabe tow hooks front and rear

INTERIOR:
- Evo 2 Plus driver seat
- Evo 2 passenger seat
- Sabelt harnesses
- Defi oil temp, oil press, boost, and EGT
- Defi pod
- Lathe Werks shift knob
- Turbosmart BC gauge in left vent