World One Performance Blog

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.

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.