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The WRX/STI/LGT/Forester XT Power Mod Path, Part 7

October 30th, 2009 No comments

The time has come for the final blog post in this series. In the last blog entry, we talked about turbo upgrades, and this blog will discuss the proper supporting modifications needed for a turbo upgrade, along with building up the motor. This of course is where all the basics end.

So you’ve got your exhaust, engine management, and you know what turbo you’d like to upgrade to, but you can’t just slap that bigger turbo on and call it a day. The reason why it’s not quite that simple is because the turbo adds much more air to the motor, thus you need to balance it out with additional fuel, cooling, air flow, and of course, a tune to balance everything out, since the stock ECU will not be able to compensate properly for the amount of air the turbo is going to need. Thus, after you’ve figured out what turbo you’d like to upgrade to, you also have to plan on upgrading the following (if you haven’t already):

  • Fuel pump
  • Fuel injectors
  • Air intake
  • Intercooler
  • Engine Management

If you’ve been following our discussed mod path thus far, chances are you already have some sort of engine management, but probably not a larger intercooler or air intake. With an upgraded turbo, you’re going to need all of these, along with fuel system upgrades. We’ll go ahead and start with the fuel system upgrades first.

For most small to moderate-sized turbo upgrades, a simple Walbro 255lph fuel pump is more than capable of pumping out enough fuel for your needs. Walbro fuel pumps are pretty much a staple when it comes to fuel pump upgrades, and will be more than enough up to about 500 whp. If you decide to go with a turbo that’s going to put out more than 500 whp, then you’re going to need a fuel pump system capable of supporting your turbo’s thirst. There are a few options out there, such as dual Walbro pump, Bosch high flow pumps, and Aeromotive fuel pumps. Each of these is capable of doing the job properly, but we’ve had our best success with the Bosch and Aeromotive fuel pump upgrades. The thing to keep in mind however is that all of these options aren’t a direct replacement for your stock pump like the standard single Walbro pump, as you’re going to need additional lines, fittings, etc. As you can see, we’re definitely getting out of the basics now.

Of course, an upgraded fuel pump is no good if they don’t have the proper injectors to actually put the fuel into the motor. Stock WRX fuel injectors are 440cc, whereas stock STI fuel injectors are 560cc. However, this is further complicated because the WRX and the 07+ STI uses a top feed style injector, whereas the 04-06 STI uses a side feed injector. The jury is out on why Subaru decided to change this and then change it again, but it’s just another complication that you need to keep in mind. Thus, if you’re upgrading your WRX to use a VF39 off an STI, you can’t just swap in the stock STI fuel injectors unless you get the 07+ specific ones. They simply will not fit.

The size of your fuel injectors is going to depend on the size of the turbo they’ll be supporting, but generally it’s better to be capable of more fuel than to run out of fuel. On that same token, you don’t want to go too overboard either. For example, if you’re running a VF39 on your WRX, there’s absolutely no need to go with 850cc fuel injectors. This causes problems not just in the fact that there’s too much fuel available, but it’ll ultimately frustrate your tuner when they try to scale the injectors down properly. Generally, here’s what you’d be shooting for in terms of fuel injectors:

For 2.0L WRX

  • 16G to VF34: 560cc – 740cc injectors
  • 18G or larger: 740cc – 850cc injectors

For 2.5L WRX, STI, LGT, and FXT

  • 18G to 20G: 740cc – 850cc injectors
  • FP Green to GT35R (pump fuel, low boost): 850cc injectors
  • GT35R (race fuel, high boost) and larger: 1000cc or larger injectors

Again, the above is all generalizations, since the amount of fuel you’ll need is also dependent on the amount of boost (and thus forced air) you’re going to be running. It’s also important to keep in mind that 850cc is pretty much the limit that the stock fuel pressure regulator will be able to handles, so if your car requires 1000cc injectors or larger, you’re going to have to replace your fuel pressure regulator with an aftermarket one, such as a Turbosmart or Aeromotive. On top of this, not every company makes direct swap-in 1000cc fuel injectors, so it’ll be important to make note if there’s anything you need to splice or add in order for the fuel injectors to function and install properly.

All right, so now you figured out your turbo, your fuel upgrades, and probably your intercooler and intake too. Of course with most rotated turbo setups, the intercooler piping and intake are typically included with the kit, otherwise you’re off to do something custom on your own. Once all of your new parts are installed, all you need now is a good tune for your choice of engine management and you’re pretty much off to the races! But wait, what about building up the motor? Are you even going to need it? In our experience, building the motor is typically dependent on a few things: tuning, size of the turbo, amount of boost you’ll be running, and your choice of fuel. For 99% of the street builds we’ve done, which are all at or below 450 whp, there really is no need to build the motor at all with proper tuning. Even at this power level in a racing situation, a proper tune has shown to keep a motor happy and healthy. For example, throughout the entire 2007 Time Attack Race Season, Phil from Element Tuning competed and won races across the country with his 2006 STI with a bone stock motor. His car was consistently powered between 450-500 whp on race gas in one of the most punishing types of racing possible, yet it still held up great and he never had a problem. Since he decided to add more power to the car in the 2008 season, he eventually built up the motor, but for all of 2007, everything was great. This shows that proper tuning is key to making sure your motor stays healthy, especially since no matter what you decide to build a motor with, a bad tune will still make it pop. Like pretty much all shops, we have our preference in terms of cost, availability, and reliability, but as long as you follow the formula below and stick with a trusted brand, everything should work great.  Here’s what we recommend if you’re sure you’ll be above the 450whp level, based on our experience:

  • Forged Pistons – The stock pistons tend to be the first thing to go given enough boost, since they are cast.  Forged pistons are typically the first and foremost part that we recommend replacing.
  • Forged Connecting Rods – These are also a smart thing to replace if you’re going to be replacing the pistons anyway. Forged rods will stand up to more stress and thus keep your motor healthy in the long run.
  • High Performance Main and Rod Bearings – The bearings are always smart to replace if you’re going to have everything taken apart to begin with.  We always replace the bearings when we have the motor apart.
  • High Performance Camshafts – Building up the bottom end was the “easy” part, but building up the heads is a completely different story. The one thing to keep in mind about the cams is that all of them will shift your powerband toward the top end, thus we usually don’t recommend cams for someone who wants low-end/street power.
  • High Performance Intake and Exhaust Valves – Valves will definitely help cams breathe, but aren’t always a necessary item, as it all depends on how big of a build you’re doing.
  • Titanium Valve Springs and Retainers – If you’re going to replace the valves, you might as replace the valve springs and retainers too. This will help the valves perform properly and stand up to more power you throw at the motor.
  • Oil Pump and Oil Pan – If there’s one thing that a build motor and big turbo needs, it’s proper lubrication of its parts. A high volume oil pump helps keep the oil flowing when needed, and most aftermarket oil pans not only hold more oil, but also act as a heatsink to help keep the oil cool. In our experience, external oil coolers actually tend to inhibit the flow of oil and since Subarus already come with an oil cooler from the factory, we usually don’t recommend any sort of external oil cooler.
  • Headstuds – You want to make sure there’s a good seal when you put the motor back together. Thus, getting proper headstuds that can take the pressure are very important.

And with that, we pretty much have an awesome motor that can handle almost anything you can throw at it. Sure, you can go with a sleeved block and increase displacement, but if that’s really your goal, you probably wouldn’t stopped reading this a long time ago, since that’s WAY beyond the basics. In any case we’ve built cars that are capable of well over 650 whp with all of the above build motor mods, which is going to be more than enough to satisfy just about everyone. I hope you’ve enjoyed this series of blog entries, and I hope it’ll remain as a good reference to all Subaru enthusiasts out there. Happy modding!

The WRX/STI/LGT/Forester XT Power Mod Path, Part 6

September 10th, 2009 7 comments

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!