World One Performance Blog

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!

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.

Continuing from the other day’s blog, you can see we’re obviously a day behind. But, let’s continue without delay!

The UTEC quickly became the go-to form of engine management between 2003 and 2004, but soon Cobb released their own AccessPort to compete with the UTEC. The AccessPort was a reflashing device instead of a piggyback ECU, which offered several advantages. Being a reflashing device, nothing needed to be installed between the stock ECU and the car (like how piggybacks are installed), and since it reflashed the stock ECU, it was similar to the ECUtek in terms of tuning resolution. Since this reflashing was done through the car’s OBD-II port under the steering wheel, the AccessPort could also be used to log and/or display types of data, such as RPM, throttle position, and more. The AccessPort also included pre-made basemaps for specific engine mods, which made it just as easy, if not easier to use, than the UTEC for those who are not interested in doing their own tuning. Cobb eventually released their own AccessTuner to allow users to do their own tuning, but it was a separate option and not included as part of the standard AccessPort package. For those who didn’t care to tune their own car, Cobb gave their dealers with AWD dynos the option to do “Protunes,” which allowed for professional tuning via the AccessPort at a shop. These Protunes could also be saved and distributed, so many Protuners released their own maps to match specific modifications as well. Despite some initial hiccups to get all of the basemaps working properly and safely for all vehicles, the AccessPort went on to become a huge success for Cobb Tuning, and it eventually overthrew the UTEC for the king of the hill in affordable engine management.

However, the basemaps that both TurboXS and Cobb supplied did have their disadvantages. In order to maintain safety, these maps were tuned for the lowest common denominator and were specific per octane level as well, to ensure that customers would not blow up their motors. While they still improved performance over being untuned and they kept the motor healthy, there was still always going to be room for improvement with a custom tune for each specific car. This still remains true today, although the margin for improvement has been able to shrink with some new engine management options available. The other problem (although not a problem for most people) is that you typically have to follow a specific mod path for the basemaps, and if you stray away from that, you have to get a custom tune for your car no matter what. While for big horsepower applications a custom map is a given, simply changing your intake away from the stock airbox is enough to warrant a custom tune, except for intakes specifically developed by TurboXS and Cobb Tuning respectively. As mentioned in the previous blog, the stock airbox is rather efficient so this may not be a big deal, but not being able to change the intake without a custom tune does put limits on your freedom of modification. Striving for more freedom of modification, other companies sought out to create another option for those people who wanted to not only wanted more freedom than he UTEC and AccessPort offered, but also get away from the limits of the stock ECU itself.

Enter the Element Tuning Hydra EMS. In 2005, Element Tuning entered the fray with their version of the Hydra EMS. The Hydra is a standalone ECU that completely replaces the stock unit. While standalone ECUs of the past required the user to tune every aspect of the car’s behavior from simply idling all the way up to wide-open throttle, Element Tuning took this difficult and time-consuming process out of the equation by taking care of all this programming already, as well as shipping the Hydra with basemaps specific to each car’s modifications, much like the UTEC and AccessPort. Moreover, Element also had maps available for a wide variety of different sized turbos, water/alcohol injection, and different sized intercoolers and intakes. The Hydra also had equal or better tuning resolution than the stock ECU, thus a basemap from a Hydra would typically be more accurate than that of a UTEC or AccessPort. This lowered the amount of custom tuning that would need to be done, but of course a custom tune per vehicle would also bring out the full potential of the car’s setup, which of course was easily possible with the provided software. On top of all this, the Hydra was also very adaptable to different environmental conditions, so the problem of having a map tuned for sea level and then needing a completely different map for mountain passes was effectively eliminated. Our own World One STI back in 2004 actually had a prototype Hydra EMS that helped it finish 2nd in its class and 6th place overall at the very first Primedia Time Attack. However, as good as this system is for tuning and adaptability, it also had its disadvantages, especially for daily drivers. The main issue is that because it’s a replacement to the stock ECU, it does not support OBD-II, and thus it will not pass emissions in just about every state in the country. The other issue, although it may be a very minor issue to some, is that you also lose your cruise control, however this is problem is apparently being fixed for the 08-09 STI. AEM soon followed up with their own plug-n-play Hydra EMS, but not until just in the past year, so support and available tuners aren’t quite as available at this time currently.

Since the release of the Hydra, both TurboXS and Cobb Tuning have updated their UTECs and AccessPorts respectively to add more features, but yet another option was introduced in 2006 that has since thrown the engine management market on its head. A group of computer-minded enthusiasts put their minds together and were able to connect to the stock ECU and then go on to start programming it. It took awhile to get things reliable and easier to use, but as it stands today, this Open Source style of tuning using the OpenECU software has become an easy entry point for customers to start tuning their own vehicles, especially since the software itself is free to download. The only purchase necessary is the Tactrix cable, that allows you to connect your laptop to your car’s OBD-II port (much like how the AccessPort connects). While OpenECU is always in a state of development, many tuners have embraced the software and use it as their primary form of tuning, allowing them to tune to the same levels as that of the AccessPort and ECUtek. Of course, the drawback is that you have to rely on user support rather than having any guarantees or formal support from a company, so in many cases, you’re on your own.

Overall, Subaru owners should be thankful that they have so many choices available to them. This isn’t the case with other makes such as Mitsubishi and Nissan. No matter what form of engine management you choose, it’s always important to understand that how well your car performs is going to depend on how the car is tuned, whether that’s strictly from a basemap or from a custom tune. If you go with a custom tune, be sure the you go to a reputable tuner that has experience tuning the type of setup that you have. After all, just because someone can tune a 300 whp car doesn’t mean that they won’t have any problems tuning a 600 whp car. As always, if you have any questions, please feel free to contact us or post a comment here. For our next part in this series, we’ll be talking about intercoolers, both top mount and front mount, and how they can affect your car’s behavior.

Last week, we finished discussing the different downpipe options out there, but before we get started with intakes and engine management, I just want to make note of the title change of this particular blog series. The reason for this is that it was mentioned to me by a reader (thanks, Mike!) that this same advice will also apply to Legacy GT and Forester XT owners as well. While some of the designs of the exhaust components may be different, the motors all behave similarly since they’re almost exactly the same anyway. Thus, if you’re a Legacy GT and/or Forester XT owner, don’t fret: these same mods will work for you too!

Anyway, we’ve covered the turboback portion of the exhaust, so now let’s talk about the intake. Just like with some of the exhaust myths we previously discussed, the intake has many myths associated with it as well. Some people have insisted that any and all aftermarket intakes are bad for your car, and that your car will soon near explode if one is installed. This blatant generalization is really quite false, and while some aftermarket intakes do not work as well or are as properly-designed as others, putting on an aftermarket intake is not going to spell instant death for your Subaru. In fact, it was proven in the November 2008 issue of Subiesport Magazine that intakes do make a difference, and that certain intakes are definitely better than others, especially after tuning. Thus, if you’re afraid that getting an intake is going to hurt your car, as long as you choose wisely, everything should work out just fine. While the stock airbox is actually very efficient and is already by design technically a cold air intake, an aftermarket intake will provide a noticeable increase in throttle response, since the higher flow of air will help your engine rev faster. This higher flow of air however can pose some problems, especially the farther along you go in your power mod path.

These problems arise when choosing your engine management options. Unlike other cars, such as the Evo, the stock Subaru ECU (or “engine control unit”) can be very temper-mental, depending on the mods you put on the car before tuning. Just like how the myth propagated that an aftermarket intake will blow up your car, a similar myth has been attributed to the turboback exhaust system, with some claims that installing a turboback will void your warranty. This is absolutely not the case, and we’ve even fought a local Subaru dealership and won in a warranty fight, with Subaru of America themselves ordering the dealership to provide warranty service to our customer’s car. In any case, this “if you install this mod, you’ll blow up your car” nonsense ties in to engine management, since now the phrase has become “if you install this mod, you’ll blow up your car UNLESS you get some engine management.” The truth is, YES, your car will perform better when tuned properly with good engine management, and YES your car will be more reliable and safer when tuned properly with good engine management, but NO your car will NOT blow up just because you installed an aftermarket intake and an aftermarket turboback exhaust system. Obviously, this doesn’t take a person’s driving style into account, but the whole idea of instantaneous motor death is ridiculous at best. We still very much recommend engine management at this point, but more because it’ll truly bring out the full potential of the car (especially when tuned properly) and because the car will perform better and more reliably, but not because it casts some sort of protection charm over you motor.

So, if engine management isn’t absolutely and completely necessary at this point, at what point is it? The intake and turboback modifications we’ve discussed are still really basic bolt-ons, thus the temper-mental stock ECU can still do its job without too many problems. However, the additional airflow both into the motor and out of the motor does confuse the stock ECU a bit, hence why engine management at this point is definitely recommended to get the ECU back on the right path. Beyond this point, when you add even more air flow (such as a bigger turbo, intercooler, and intake) and also more fuel (such as larger fuel injectors), the stock ECU simply does not know what to do, and thus engine management is absolutely necessary. Often times, the car simply will not idle or run at all without engine management and these additional mods. Thus, to put it plainly: for an intake and turboback, you’ll probably be just fine, but for anything more than that, you’ll definitely want engine management.

Now that you found a need for engine management, either because you’re going with big power mods or because you just want your turboback to perform to its fullest potential, what’s the best engine management choice? This is where things could potentially get complicated. There are three main forms of engine management available for Subarus:

ECU Reflash

• Cobb Tuning AccessPort
• OpenECU
• ECUtek

Piggyback ECU

• TurboXS UTEC
• Dastek Unichip

Standalone ECU

• Element Tuning Hydra EMS
• AEM EMS
• Tec3
• LinkECU
• MoTec

While each of these forms of engine management accomplish the same basic principles, they each do it in different ways, and ultimately to different levels of success as well. An ECU Reflash uses the stock ECU, but loads different maps on it to control the motor, allowing the stock ECU to still control other functions such as the HVAC and cruise control. Piggyback ECUs are small computer devices that act as a middle man between the stock ECU and the rest of the car, with one end plugged into the stock ECU and the other end plugged into the car’s wiring harness. Finally, standalone ECUs completely replace the stock ECU with a new one.

Back when the WRX first made its way across the Pacific in 2001, the two main engine management solutions available at the time specifically for the WRX were the ECUtek reflash and the Dastek Unichip, which was offered by TurboXS and Vishnu Performance. The ECUtek reflash worked and still works well, but the license to be an ECUtek programmer was/is on the very expensive side, so typically these reflashes needed to be performed by a shop every time. The TurboXS and Vishnu Unichips on the other hand had a pre-installed basemap to suit specific level of car modification right out of the box, and could be further programmed by an authorized tuning shop specifically for each vehicle. The difference between the different company’s Unichips was how the basemaps were programmed and how they would connect to the car, either via a wiring harness or if they had to be hard-wired. It was from TurboXS’s “Stages” that we get the Stage 1 to 4 levels that we still use to this day: Stage 1 was for a Unichip and catback only, Stage 2 was for a Unichip and Turboback, Stage 3 was for an added larger intercooler, and Stage 4 was for an added larger turbo, injectors, and fuel pump. Anything more than that was simply considered “Stage 4+”. Since both Unichips came with a preloaded map to match your level of modification and it was a relatively easy install, the Unichip was by far the more popular option at the time. However, one problem with these preloaded basemaps is that they were designed specifically for the airflow of only the stock intake airbox, and thus aftermarket intakes were not compatible with the preloaded basemaps, and therefore required custom tuning. This caveat has been an issue with many later forms of engine management, including the Cobb Tuning AccessPort we all know and love today. Nevertheless, people (myself included) happily removed the aftermarket intake they purchased and reinstalled the stock airbox to ensure that the Unichip was happy and performing properly. Standalone ECUs such as the Tec 3, LinkECU, and MoTec existed, but since they did not have the same plug-n-play functionality of the Unichip, they were often only used by more hardcore WRX modifiers. After all, the last thing most customers want to do is spend hours tuning their ECU just to get their car to idle correctly, let alone actually increase performance over stock.

Over time, the Unichip started to show some problems. For one thing, certain Unichip owners would find that the pre-loaded basemap on their Unichip would either simply be erased over time, or the stock ECU would actually override the Unichip, rendering it completely useless. The Unichip’s tuning resolution (the actual increments and scale of tuning certain things such as air/fuel ratio and ignition timing at specific RPM) was also nowhere near that of the ECUtek, so even the custom tunes did not end being as good as they could have been with better resolution. Given the problems they were having, TurboXS went on to develop and release the User-Tunable Engine Computer, or “UTEC.” The UTEC was a big step forward in not only tuning resolution, but because it allowed the user themselves to actually tune their car, rather than requiring a shop to tune it for them. TurboXS still provided basemaps to start from, and the user could load them onto their UTEC via laptop or taking the UTEC out of their car and plugging it into their home computer. This opened up a world of possibilities for many people, some of which are now prominent tuners who first started out tuning on the UTEC. Vishnu attempted to answer TurboXS’s ante with their own “XEDE,” but the XEDE proved to not be quite as versatile or as easy to use as TurboXS UTEC, and soon Vishnu abandoned Subarus and moved on to the brand new Evo market (which they also eventually abandoned).

See as this blog is starting to get quite lengthy, we will conclude this discussion on engine management in tomorrow’s blog.

Yesterday, we discussed the choosing of an aftermarket catback system to the WRX or STI, not only for additional power, but also for aesthetic purposes. However, as much as we all love the boxer sound, in terms of actual measurable power, the catback alone really doesn’t do much. Thus, after the catback, the next power mod most people consider is an aftermarket downpipe. The downpipe is where the true power starts to be made, since as you can see from the photo to the right, the stock downpipe has 2 power-robbing catalytic converters, or “cats” for short. In this photo, the downpipe on the bottom is the stock downpipe, whereas the downpipe on the top is an Invidia catless downpipe. In comparing the two downpipes, you’ll also notice a few differences other than the cats: the stock downpipe is split into two pieces (some people and manufacturers only refer to the top-most section as the downpipe, and the second section as the midpipe), and the flange at the top that connects to your turbo has a flat plate. These two differences are clear examples of how different companies prefer to approach creating an aftermarket downpipe.

Before we go further however, we must make a disclaimer: removal of the stock catalytic converters is for off-road use only, and if caught using a catless system on the street, you may be cited and fined. In other words, you do have to pay to play, so make sure you’re well aware of this, especially in states like California where emissions laws are very strict and may involve impounding your car if violated. Now that that’s out of the way, most aftermarket downpipes have the following features that are geared as improvements over the stock downpipe:

• Removal of all cats or replacing 1 or 2 cats with high-flow performance cats
• Replace the flat flange at the turbo side with a “bellmouth” or “divorced wastegate” flange
• Change from a 2-piece pipe to a 1-piece pipe

Of course, just the same as with catbacks, not every downpipe is equal, and this is even more clear with the different designs out there. No matter the design though, the main thing that really should be considered is fitment. Some downpipe have problems fitting due to hanger location, but others simply have issues with fitting because they’re made to mate to their own proprietary exhaust system, so they might require a separate pipe for it to connect to the aftermarket catback of your choice. On top of this, most aftermarket downpipes will not bolt on directly to the stock catback for 02-07 WRXs and STIs, however this is completely the opposite for 08-09 WRXs and STIs, which don’t have any problem bolting to the stock catback. Why would you want to bolt onto the stock catback you might ask? Well, although you do sacrifice power by sticking with the stock catback (since it creates a bottleneck), you do get a significant power increase over stock and you don’t attract any unneeded attention from the authorities.

Once you’ve sorted out fitment issues, the next thing to consider is going catless or staying green-friendly with a high-flow cat. It has been argued that a good high-flow cat will not hamper power at levels below 400 whp, but in our experience, this has not been the case whatsoever. Moreover, running catless helps with throttle response and faster turbo spool since there’s no back pressure in the exhaust system to slow down the exhaust flow. It has also been argued that running catless creates a bad exhaust smell in the cabin, but while this may be the case when a catless downpipe is initially installed, the smell does go away over time, so long as the downpipe was installed properly with no leaks. And, since catted downpipes are typically almost twice as expensive as catless downpipes, unless you absolutely need a catted downpipe for emissions or racing restrictions, we always recommend a catless downpipe. Catless? But what about the check engine light? Well, certain forms of engine management will turn off this check engine light for you, but we will get into that when we talk about engine management in a future part of this blog series.

After deciding on whether to go catless or catted, the next big decision is in regards to the downpipe’s flange at the turbo side. Here are a few examples of the available options, other than stock downpipe’s flat plate design. First up is the “bellmouth” design, which looks like this on the TiTek downpipe:

Next up are two variations of the “divorced wastegate” design. The idea behind the divorced wastegate is that a stock style turbo has exhaust gases the escape from the turbo’s internal wastegate, and since that might cause turbulence when mixed in with the ordinary exhaust gases that exit the turbo, it’s better for these gases to exit out separately so that the exhaust flow is not interrupted. The first one is Invidia’s version, which is essentially just a flat divider plate that diverts the gases, but the gases still go down the same exact pipe further along:

In contrast, here is Element Tuning’s take on the divorced wastegate design. This downpipe actually features a completely separate pipe for the wastegate gases, which then meets up later on with the rest of the piping. The theory behind this is that it’s a true divorced wastegate and the extra smaller piping creates a venturi effect which makes the wastegate gases not only flow faster, but also create a suction effect that makes the rest of the exhaust gases flow faster as well:

In our experience, we definitely recommend either of the above styles. It’s best to stay away from the stock downpipe’s flat plate style, which can be found on a few downpipe brands out there. However, between a bellmouth and Invidia’s divorced wastegate style, we have not seen or felt a significant difference in power. On the other hand, Element Tuning’s divorced wastegate style has proven to produce more power over the other styles.

Finally, you’ll notice that Element Tuning’s downpipe is a 2-piece design, whereas the Invidia design is a 1-piece. Generally speaking, a 1-piece tends to be better when avoid exhaust leaks, but a 2-piece design gives the option to change from a catless race pipe to a catted pipe at your discretion. Not every 2-piece downpipe has an option for a catted downpipe however, so it’s best to do your research (as always) before purchasing. Nevertheless, if you have any further questions, again please don’t hesitate to contact us. For the next blogs, we’ll change gears a little bit and highlight some products and feature a customer car, but next week we’ll come back to the power mod path with a discussion about intakes and engine management.

Undoubtedly, one of the most popular inquiries we receive from new WRX or STI owners who have been bitten by the mod bug is, “how do I get more power out of this car?” Ever since the first original 2002 WRX commercials back in 2001, people have always bought this car to go fast, and with the right combination of modifications, going fast is relatively easy. In the next series of blogs, we’ll be strictly discussing power modifications, all the way from the basics to more power than you’ll likely ever truly use in the lifetime of your car. Although the vast majority of these modifications are bolt-ons, there’s always going to be some pros and cons to each mod, whether it be in driving characteristics or simply not being street legal. We will definitely discuss these pros and cons as we go along and we will make it a goal to make this discussion easy enough to understand for someone who is completely new to cars, let alone Subarus in particular.

Before we jump into the thick of things, it’s important to remember that while there’s a lot of different “Stage” numbers being thrown around, these stages are not universal. Back in 2002, TurboXS came out with their own “Stage 1-4,” and then later Cobb Tuning came out with their own “Stage 1 and 2,” but there really hasn’t ever been an officially agreed upon requirement of certain mods to reach a specific “Stage.” We will however mention what unofficial “Stage” we’re at as we go along.

Just about the first power mod that enthusiasts would like to do is to give their WRX or STI a voice with a replacement catback system. This is a good starting mod, as it doesn’t require any re-tuning and the install is as simple as undoing and redoing a few bolts. The catback replaces the stock piping you’ll find here in this old, yet still very helpful diagram:

It should be noted though that not all catbacks are created equal, and this rings true for all the other components of the exhaust system as well. Many people find it hard to justify spending $600-700 for a catback when they can buy one for $150-300 on eBay, but the truth really comes out in the manufacturing. All too often I hear accounts from eBay-brand exhaust owners who after only 1-2 years of ownership , must clean the rust off of their exhausts at regular intervals, even though they do not live in a climate where it snows and thus there’s no salt-based de-icing agents on the road. This really should not be the case whatsoever, and the higher priced exhausts are almost always more resistant to rust, so much that they maintain their quality for many years. Other differences to consider between the very inexpensive exhausts and the higher priced exhausts are the design of the exhaust itself, how well the exhaust fits on the car, how good the welds are on each of the pieces, and the manufacturer’s warranty. The difference is really in the detail.

The next thing to consider overall is the piping diameter and design, but honestly most people seem to read into this more than necessary. A turbo motor likes to breathe, and thus the better the exhaust flow, typically the better the car performs. Most catbacks and downpipes are made to be 3 inches in diameter for the most part, however many, if not most catbacks taper down to 2.5 inches at the end that bolts onto the downpipe. The reason for this is to make it easier for the exhaust to mate to the rest of the otherwise stock exhaust, but over the years some people have claimed that this tapering down is a huge and unacceptable hindrance. While this taper can be an issue with high horsepower levels (400+ whp) since it creates a bottleneck, the vast majority of WRX and STI owners, especially those who do not track, compete, or otherwise race their car on a regular basis (in other words, daily drivers) will never feel or notice this power difference. That isn’t to say that full 3-inch piping that does not taper down to 2.5 inches is a bad thing, rather it simply shouldn’t be of the utmost priority for the vast majority of Subaru owners out there. What really should be important though is whether or not the exhaust is straight-through or if it is baffled. Straight-through exhausts tend to be louder, but there are definitely some quiet ones out there. The problem with baffled exhausts is that while they tend to be more on the quiet side, the exhaust flow goes through a baffling chamber which causes the exhaust to be quiet. This interrupts the exhaust flow and thus will not make as much power as a straight-through exhaust. You’ll be able to tell the difference pretty easily: if you look down one end of the exhaust and can see light at the other end with little problem, you’ve most likely got a straight-through exhaust. Otherwise, the exhaust is most likely baffled, and the exhaust flow has to make some twists and turns in the baffling chamber before it exits out the other side.

Finally, probably the most important thing to consider about the catback of your choosing is how the exhaust itself sounds. Choosing an exhaust sound is much like choosing a set of wheels or a pair of shoes, since everyone has different tastes and needs. Some exhausts are deafening loud, whereas others are just as quiet as your stock exhaust. Generally speaking, the louder the exhaust, the more straight-through it is, and thus the more power it makes, but there will always be exceptions to this rule. If you live in a state where exhaust volume levels are strictly enforced, then you’ll definitely want to consider a good, straight-through, quiet exhaust. Otherwise, almost nothing sounds as good as a very loud WRX or STI, but just be prepared to deal with exhaust drone on the highway and having to yell simply to converse with your passengers.

That just about does it for part one. Be sure to do your research, watch some exhaust videos on your favorite video hosting website, ask your friends’ opinions, and be sure to contact us if you have any further unanswered questions. We’ve come across more exhausts than most other vendors in our day, so we’ll be happy to make a recommendation for your needs! Tomorrow, we’ll talk about the next component of the exhaust system: the downpipe.

Continuing off from yesterday’s wheel offsets discussion, since the vast majority of our clients are Subaru Impreza owners, it only made sense to discuss wheel sizes and options that fit on the Impreza, and the potential problems that might arise. As mentioned yesterday, heels have to clear 3 main things in order for them not only to fit on the car, but also roll freely: fenders, suspension, and brakes. To add complexity to this, the wheel diameter, width, offset, and even spoke design come into play. For example, even though a wheel might have a diameter, width, and offset that works fine, another wheel with the same exact measurements but a different spoke design might not clear the brakes. And of course, this depends on the brakes being used, whether it’s the stock STI Brembos, a StopTech BBK, or the 06-07 WRX calipers. The good thing though, is that we’ve installed a number of different wheel and tire setups here at our shop, so we can speak with confidence on the combinations I’m about to mention. I’ll also include the necessary suspension and/or fender modifications required for these wheels to fit without any rubbing.

For 02-09 WRX and 04 STI

The WRX and 04 STI are plagued by the 5×100 bolt pattern. This pattern is the actual distance that the lugs are spread apart on the wheel hub. While you wouldn’t think that a 14.3mm difference between the WRX and STI is a big deal, as it turns out, the wider the wheel and the lower the offset you go, the more stress you put on the wheel bearings in this bolt pattern. For this reason, many of the wheel manufacturers that we carry do not even make certain wheel fitments for 5×100. Here are a few examples that we have personal experience with:

• Volk TE37 17×8 +44 5×100 (clears STI Brembos)
• Volk TE37 18×7.5 +48 5×100 (does NOT clear STI Brembos)
• Volk CE28N 17×7.5 +50 5×100 (does NOT clear STI Brembos)
• Volk CE28N 17×9 +43 5×100 (clears STI Brembos, may require fender rolling depending on tire)
• Volk CE28N 18×8.5 +44 5×100 (clears STI Brembos)
• Volk GT-V 18×8 +46 5×100 (clears STI Brembos)
• Volk GT-S 18×8 +43 5×100 (clears STI Brembos)
• Gram Lights 57 Maximum 18×8.5 +45 5×100 (clears STI Brembos)
• Gram Lights 57 Optimise 18×8.5 +43 5×100 (clears STI Brembos)
• 57Motorsport G07WT 17×9 +45 5×100 (clears STI Brembos)
• Advan TC-II 18×7.5 +48 5×100 (does NOT clear STI Brembos)
• Advan T6 18×8 +45 5×100 (clears STI Brembos)
• Advan RS 18×8.5 +48 5×100 (clears STI Brembos)
• Advan RC-II 18×7.5 +48 5×100 (does NOT clear STI Brembos)
• Prodrive PWRC1 18×7.5 +46 5×100 (clears STI Brembos)
• Prodrive GT1 18×7.5 +53 5×100 (does NOT clear STI Brembos)
• Enkei RPF1 17×8 +45 5×100 (clears STI Brembos)
• Work Emotion CR Kai 18×7.5 +42 5×100 (clears STI Brembos)
• Work Emotion XD9 18×8 +45 5×100

As far as tire sizes go, you are of course limited to the width of the wheels that are even available to 5×100. In most cases, you can run a 245/35/18 tire no problem without any rubbing issues, but you can also run a 245/40/18 if your car isn’t lowered very much. However, a 255 tire will definitely require fender rolling and/or cutting.

For 05-09 STI

The change to the 5×114.3 bolt pattern opened up a plethora of wheel options to STI owners. Since 5×114.3 is a more universally-available bolt pattern, just about every wheel manufacturer had varying sizes of wheels that would fit. 8 and 8.5 wide fitments were almost always safe without any risk of rubbing, so long as you didn’t roll with a 245 or larger tire size. A 235 tire size is almost a sure-fire perfect fit with no rubbing issues. However, with more wheels available in 9 and 9.5 inch widths, the trend moved toward these wheel and tire sizes, which almost always require fender modification. Specifically for 9.5 inch widths, coilovers were required for suspension clearance along with rear camber bolts in order for the wheels not to rub on the fenders, which of course needed to be rolled anyway. Again, a few examples, each of course clears STI Brembos:

• Volk CE28N 18×8.5 +52 5×114.3
• Volk RE30 18×8.5 +52 5×114.3
• Volk RE30 18×9 +50 5×114.3
• Volk TE37 18×8.5 +50 5×114.3
• Volk CE28N 18×9.5 +40 5×114.3 (requires fender rolling, coilovers, and rear camber bolts for 05-07 STI only)
• Gram Lights 57 Maximum 18×8.5 +45 5×114.3
• Gram Lights 57 Optimise 18×8.5 +43 5×114.3
• Gram Lights 57F 18×8.5 +45 5×114.3
• Advan RG-II 18×8 +45 5×114.3
• Advan RS 18×9 +45 5×114.3
• Advan RZ 18×9 +45 5×114.3
• Prodrive GT1 18×8.5 +53 5×114.3
• Prodrive GC05F 18×8.5 +44 5×114.3
• Prodrive GC010G 18×8.5 +46 5×114.3
• Prodrive GC05F +44 5×114.3 (requires fender rolling, coilovers, and rear camber bolts for 05-07 STI only)
• Prodrive GC010G 18×9.5 +44 5×114.3 (requires fender rolling, coilovers, and rear camber bolts for 05-07 STI only)
• Prodrive GC010E 18×9.5 +44 5×114.3 (requires fender rolling, coilovers, and rear camber bolts for 05-07 STI only)
• Prodrive GC06H 18×9.5 +44 5×114.3 (requires fender rolling, coilovers, and rear camber bolts for 05-07 STI only)
• Enkei NTO3+M 18×9.5 +40 5×114.3 (requires fender rolling, coilovers, and rear camber bolts for 05-07 STI only)\
• Work Emotion XD9 18×9 +43 5×114.3
• Work Emotion CR Kai 18×8.5 +43 5×114.3

Obviously, with wider wheels, you can run wider tires. As mentioned above, just about everything 255 and up will require fender rolling, but we’ve managed to fit 265/35/18 and 275/35/18 after fender and suspension modification as mentioned above. The Element Tuning Time Attack Race Car pictured above runs on Prodrive GC05Fs in 18×9.5 +44 5×114.3 and 275/35/18 Hankook race slicks.

For 08-09 STI

The wider track and fenders of the 08-09 STI definitely allow for even wider wheels and tires, with much less risk of rubbing. This is partially due to the fact that the 08-09 STI comes with 18×8.5 wheels straight from the factory. All of the above wheels fit perfectly fine on the 08-09 STI, however 265 and wider tire sizes may require fender rolling, depending on how low of an offset you decide to run. Generally speaking, staying with a 05-07 STI safe offset will not require any fender modification on the 08-09 STI, and any of the 18×8.5 wheel sizes can simply reuse the stock Dunlop 245/40/18 tires. Fitment examples:

• Volk CE28N 18×9 +35 5×114.3
• Volk RE30 18×9 +35 5×114.3
• Volk TE37 18×9.5 +40 5×114.3
• Volk TE37 19×9.5 +43 5×114.3
• Advan RS 18×9 +35 5×114.3
• Advan RZ 18×9 +35 5×114.3
• Work Emotion XD9 18×9 +38 5×114.3
• Work Emotion CR Kai 18×8.5 +37 5×114.3

Again, I should stress that these are all just examples that we’ve tried here at our shop, and there are very many other wheels and sizes that will fit just fine. Just remember to do your research and if all else fails, contact us and we’ll be happy to make a recommendation!

While the first thing most people do to their car is upgrade the power, often times when it comes to wheels, many people seem to be at a loss. Often people don’t know what wheels fit their car, let alone what’s a good quality brand. However, before we get into wheel manufacturing technology (which we’ll go over in a future blog entry), let’s start with the basic wheel feature that affects how wheels will both fit and look on a car: wheel offset.

Whenever your look up wheel specs, they usually have a listing of offsets, such as +53, +45, +29, and so on. These offsets represent the distance in millimeters that the wheel hub (where you actually mount the wheels onto the car) is from the centerline of the wheel. I created this diagram from a Volk TE37 for Porsche wheel to help illustrate:

As you can see, I’ve placed a line the goes down the center of the wheel, and I’ve shown that the right side of the wheel is on the outside toward the fender, whereas the left side of the wheel is on the inside toward the suspension. As the diagram shows, the wheel hub is directly on the center line, which means it has a zero offset. When the wheel hub is pushed out toward the outside of the wheel, then the wheel has positive offset; when the hub is pushed in toward the inside of the wheel, then the wheel has negative offset. Makes sense, right? Perhaps it does, but how does this affect wheel fitment?

Herein lies the problem with offset. Wheels have to clear 3 main things in order for them not only to fit on the car, but also roll freely: fenders, suspension, and brakes. Since ever car is different, not every wheel offset will work. Some cars, such as the 350Z and M3, have plenty of room between the outside fender and the suspension. Other cars, such as the 93-01 Impreza, have nowhere near as much space. Still other cars, such as the S2000 have an average amount of room in the front of the car, but barely any room in the rear. On top of all this, wheel offsets are also affected by the width of the wheel. Thus, a wheel that is only 7.5 inches wide fits differently than a wheel that is 10.5 inches wide with the same exact offset. Remember, the offset is measured from the centerline of the wheel, so the wider the wheel, the distance available from the centerline. This can very much come into play when there’s a big brake kit on the car, since you’ll need to choose an offset that will clear the brake calipers.

Despite all the possible complications, here are a few generalizations that will help with your wheel offset decisions:

• High offsets (such as +50 for example) make the wheel fit inward toward the suspension. This helps the wheel clear the outside fender, but since the wheel goes in more, it could pose problems clearing brakes or contacting the suspension.
• Low offsets (such as +25 or anything in the negative for example) make the wheel fit outward toward the fender. This helps the wheel clear a big brake kit, but it could pose problems with your wheels and tires rubbing against your fenders.
• Since every car is different, certain offsets (typically lower offsets) combined with a certain wheel bolt pattern can cause undo stress on your wheel bearings, causing them to wear out prematurely. For this reason, many wheel manufacturers simply do not manufacture wheels in certain fitments.

So how do you decide what’s the best wheel offset for your car? First off, do your research: find out what your stock wheel offset is first and foremost, and then you can even measure yourself to determine how different of an offset will suit your needs. Also find out what other people with your same car are running and find out if they have any wheel fitment problems. After you’ve done your research and you’re still unsure, please don’t hesitate to contact us, since we are familiar with a great many different wheel options and fitments for various vehicles. If you find out that the size and offset you need aren’t readily available, we can always special order you a set and, depending on the brand, even custom order a set of wheels to your exact specifications. Coming up tomorrow, we will share some typical wheel and tire fitments that we’ve tested out at our shop and what modifications were necessary to make them fit without any fender rubbing or suspension contact.