Why the COBB Accessport is the Top Mod for Your Subaru WRX/STI

    23 MAY 2024 - Jeff Willis

    COBB Tuning has been a household name in the Subaru world for over 20 years now. In fact, the Accessport is pretty much synonymous with Subaru in terms of modifications. But it goes much deeper than that. For those of you new to modifications, lets go back to square one before you get yourself into trouble. Let’s discuss the overall importance of tuning so you don’t melt your motor.

     Your ECU aka Engine Control Unit aka the brains of the operation, is programmed by the factory to control the factory-issues components in the engine. The key components that we like to upgrade are the intake system, the exhaust, as well as the fuel system. So, if you had just bought a Subaru WRX brand new off the showroom floor, or if you happen to come across a bone stock WRX or STI in a marketplace and want to start modifying for more power, there are some important things to consider.

    If you upgrade your intake system whether if it’s a cold air intake, short ram intake, or any intake system that directly replaces your factory intake box, the MAF (mass air-flow sensor) will see a larger volume of air passing through its parameters. More importantly, there is a high level of restriction being lifted as a result of an aftermarket intake. When compared to your stock intake system, an aftermarket intake will let your turbocharger inhale a larger volume of air more rapidly and this is why you get a spike in horsepower, torque, and boost response. Without a tune, you may experience boost spikes outside the parameters of where your factory boost control solenoid is programmed to control. These spikes could also boost past the limits of your factory fuel injector duty cycles. What you will experience is boost cut and fuel cut. Your engine will be stumbling hard in the upper RPM range as your ECU is not programmed to compensate the timing tables, fuel trims, and air volume outside of its factory settings. Note that this does not apply to all aftermarket intake systems due to the design, but a vast majority of aftermarket intakes will require a tune.

    The same applies to exhaust components, particularly downpipes. Like your intake, the factory downpipe is one of the more restrictive components within your turbocharger system. This is why turbocharged vehicles in general respond so well to aftermarket examples. Metaphorically speaking with your factory intake, your turbocharger is trying to breathe through a straw. When adding an intake your turbo breathes much easier. A downpipe will allow your turbo to exhale the exhaust gases without any turbulence or restrictions, and this is why an aftermarket downpipe greatly increases the horsepower. The reason why virtually every turbocharged Subaru needs a tune after installing a downpipe is because like a cold air intake, you will also see a spike in boost causing your ECU to try and compensate for these levels that have greatly surpassed the factory settings.
     

    WHAT HAPPENS IF YOU INSTALL THESE UPGRADES AND CONTINUE BOOSTING WITHOUT A TUNE?

    Every time you hit boost, those moments just before hitting boost cut or fuel cut, you could be making a lean spot. Lean spots lead to detonation. Before you know it, you’ll be shopping for a new engine.
     

    HOW DOES THE COBB ACCESSPORT MAKE EVERYTHING BETTER?

    COBB Tuning has invested countless hours along with expertise in the Subaru platform to develop proper off-the-shelf maps to download onto your Accessport to work in conjunction with your current or future modifications. It simply plugs into your OBD2 port where it makes contact with your ECU, and essentially tells the ECU what parameters it needs to adjust to compensate for your modifications. And it packs many more features for a plug-and-play engine management device when compared to having a total stand-alone engine management system. Some of the features include but are not limited to:

    • Larger, full color, higher resolution screen
    • Customizable multi-gauge display
    • In vehicle mount, with on/off switch
    • Faster and easier to use with a familiar face
    • Interchangeable faceplates
    • Very simple installation
    • Very simple uninstallation if needed
    • Has the ability to read engine codes triggered by your check engine light
    • Has multiple colored display gauges
    • Has data logging
    • Measures your performance like 60-foot times, ¼ mile times, and trap speed
    • MAPS available to download for current and future modifications
    • Maximizes your upgrades to their fullest potential

    So if you upgrade to one of COBB Tuning’s Staged Power Packages that can include sophisticated items such as larger injectors, speed density that removes your MAF altogether, or get a larger MAP sensor to run higher boost, the Accessport can provide a tune for this.
     

    WHAT ELSE SHOULD I HAVE TO GO ALONG WITH THE ACCESSPORT?

    The single most important gauge you should have in your Subaru, or any modified vehicle whether if it’s turbocharged or naturally aspirated is a proper wideband O2 gauge. The Accessport has the ability to monitor AFRs (air-fuel ratio) in the factory O2 sensor installed on some Subaru models where it is located on the up pipe. The problem is that it maxes out at 11.14 AFRs. Even with an Accessport you can still risk leaning your engine out. There are times where you can risk leaning out your engine. If you surpass the limits of your stock injectors, then you could be running a lean condition. Or if you have a dirty injector your AFRs could be out range. A good AFR reading under boost will be between 10.80 AFR which is on the fat side, to 11.80 AFR which is right at the peak of the sweet spot just before entering lean territory. You would also need a higher reading MAP sensor like a 3 BAR and above depending on what boost levels you want to achieve.
     

    PLUG AND PLAY VS STANDALONE?

    Standalone systems are for those with a race car or off-road use. Stand alone systems such as the popular AEM EMS, or the Haltech Elite or Motec M-series standalone systems are complete replacements of your ECU and give you full command and control over every parameter throughout your engine. Standalone engine management systems require compatible MAP sensors, IAT sensors, boost solenoids, as well as other sensors you can add to monitor your desired area. Standalones also must be tuned by trained professionals otherwise you can have a poorly running engine, or you can easily risk catastrophic engine damage. A plug-and-play engine management device will still use the full functioning power of your factory ECU. Like the COBB Accessport, most will plug into your OBD2 port where you can upload MAPS or make adjustments to send signals to your ECU. Now it is always a good idea that you also consult with an experienced tuner with the Accessport and one who knows their way around engines. The Accessport is not 100% fool-proof. If you don’t know what you’re doing, leave it to a professional. Tuning is not something that should be performed at the hands of the inexperienced.
     

    PROVEN RELIABILITY AND PERFORMANCE

    The COBB Accessport made its debut back in 2004 and made giant waves in the Subaru community as it was the same year the STI was released for US markets. This was the first hand-held tuning device for the Subaru platform, and nearly 20 years later, it remains as a go-to household appliance in the cabins of many modified Subarus on a global scale. It simply works well and can be easy to operate for tuners and fellow enthusiasts. More importantly, it will provide your Subaru with a safe tune with modifications as little as a drop-in intake, to a complete Stage 3 Power Package. Today, the COBB Accessport has options available for other makes and models as well, including Accessports for Porsche, Volkswagen, as well as a variety of MazdaSpeed and Ford Ecoboost models.
     

    CLICK BELOW FOR POPULAR OPTIONS

     

    ACCESSORIES NEEDED WITH AN ACCESSPORT OR STANDALONE ECU

    Because the Accessport is a simple plug-and-play piggyback tuner, tuning is as simple as downloading the correct off-the-shelf map from COBB’s website that aligns with your modifications. You can then start driving on the street to make sure all is well with your Subaru, and to make sure there are no hiccups in the RPM band. With standalone engine management systems, these are far more complex as you have full control over every parameter of the engine. The tuner will tune for what injector size you have, they need to set your throttle position sensor correctly, they need to tune for your elevation and fuel type, and they need to tune how much boost you can run.

    Both examples can be tuned on a dyno, and tuners will usually remote in, or keep your vehicle for a few days to tune when your engine is completely cold for a correct cold-start map. The COBB Accessport will rely on the ECU’s factory settings.

    Once your car is set up, and drivable, there are imperative parameters that you need to keep a hawk eye on. Because of these reasons, it is highly recommended that you have proper gauges in your Subaru especially since the Accessport is limited on fail safes, or if your stand-alone ECU is not equipped with fail safes. This is why you will need these recommended gauges to make sure your engine survives:

     

    WIDEBAND O2

    AEM UEGO X-Series Wideband Controller w/Gauge Kit

    For turbocharged, supercharged, or any modified naturally aspirated engine, your air-fuel ratios are one the most important parameters you need to monitor while under full throttle. This gauge is insurance for your engine, and it is also a proper diagnostic tool if your tune is outside of the strike zone. Under boost, your AFRs (air fuel ratios) need to be from 10.8 t0 11.8 AFR. 11’s are ideal while anything lower than 10.8 is on the rich side, and anything in the 12s and above is on the lean side. If you are running lean under boost, this means that your cylinders are not getting enough fuel, and your cylinders can get hot enough to melt your pistons. Too rich and lower than 10.8 means that you are getting too much fuel in your cylinders. If you are running so rich that your wideband gauge is reading too low, then that means you risk washing your cylinders out with fuel, and the fuel will make it to your oil to cause contamination.

    Now when your tuner has a tune locked in, the tune doesn’t magically change. If you notice that your wideband O2 gauge is out of the ordinary, this means that something mechanically is wrong. If your gauge is reading too lean, you could have dirty injectors, a weak fuel pump, or a dirty fuel pump sock. If your wideband gauge is reading too rich, you could have a vacuum leak, you might have blown off an intercooler pipe, or worse, you could have a broken piston ring. And that is why wideband O2 gauges make for a proper diagnostic tool in case your Subaru is not running right, then you can look at your AFRs and see how the car is running and go from there.

     

    OIL PRESSURE GAUGE

    Defi Advance Oil Pressure Gauge

    Oil Pressure is crucial for a proper running engine. However, with modified engines, oil pressure can be compromised because modified engines get driven harder. If you notice a loss in oil pressure, this is an indicator that you must stop your engine immediately, and check things out to prevent further damage. A sudden drop in oil change could mean that you have a spun bearing in the motor. The crankshaft main bearing journals, as well as the connecting rod journals have a constant film of oil that sits between the bearing and the journals. So, if you spun a bearing, you will immediately lose oil pressure as that bearing is now making metal-to-metal contact, shredding into thousands of metallic flakes floating in your engine, then you will need a new engine. The reason why you need to shut down the motor immediately is to prevent further internal damage that could shoot a rod out the side of your block.

    Other indicators of low oil pressure are a loss of oil from a leak, or a bad oil pump. Low oil pressure is scary yes, but you need to be the fail safe in this situation by preventing further damage to your engine so that at the least, your machine shop can save your block by cleaning everything out and to determine if any boring, or bearing re-sizing is required.

     

    VOLTMETER GAUGE

    Defi DF Blue Racer N2 Volt Gauge

    A healthy battery is required when having a modded vehicle. Especially if you have a race car, or a high horsepower street car with a standalone EMS. Most of these vehicles will have more than one fuel pump, a higher voltage alternator, and if you have a weak battery, the ECU cannot send proper signals to operate these items which can cause trouble during boost. When your vehicle is not in use for prolonged periods of time, fully charge your battery and disconnect it, or even better, make sure your battery is hooked up to a battery tender. Letting your battery die over and over will kill the battery, and your car will not operate as it should. Make sure your battery is happy, so that all of the functioning sensors, pumps, and your tune all work together.

     

    WATER TEMP GAUGE

    Defi Advance BF Water Temp Gauge Metric 60mm

    Now water temp gauges are recommended especially if you have an older vehicle. Now we all rely on the factory water temp gauge, but for cars with mods, you must know exactly where your temps are. Proper water temps during regular driving duties floats between 185-190°F. Anything above that your engine will trigger your cooling fans to come on. But if you notice your temps start to get into the 200°+ temps, you need to check your coolant levels, and you need to check and see that your fans are kicking on, or perhaps your radiator is clogged not letting air pass through. Because what are Subarus known for? Bad head gaskets, and if your engine gets too hot, your heads could warp causing an uneven mating surface between the heads and the short block. Always be mindful of your water temps. If they get too hot, shut the car down, let it cool, and do your investigating.