Why do I need engine management? Consider your stock engine management for just a moment. Your stock engine control unit (ECU) is a very complex piece of circuitry that calculates hundreds of variables every second. All of these variables rely on inputs within a + or – range. When you modify your vehicle, these values change. As long as the changes are within the values the ECU expects to receive, your engine runs fine. Once the values are exceeded, the ECU is programmed to compensate to return the values to normal levels.

This is a layman’s explanation of how your stock ECU can actually work against you when modifying your vehicle. This also explains why modifications can feel great once they are bolted on but the butt dyno results seem to fade over time. This is due to ECU compensation.

What is the first step in finding what engine management I need? Finding a tuner. The Tuner FAQ will help with the general rules of finding a good tuner. Remember, it's always better to have a custom tune vs. a plug and play or "staged" map. Always defer to the tuner's advice as to what to choose as ultimately he will be the one to provide custom support. Discuss your goals and budget and your tuner should set you on the right path. If you are a "plug and play" kind of person, review the options below and decide for yourself along with input from locals in your regional forum and the car parts review forum.

What will engine management do for me? Generally speaking, engine management optimizes several engine functions to create more horsepower and efficiency. The stock ECU is designed to ensure your car runs fine and monitors the engine’s output parameters. Utilizing an aftermarket engine management solution takes this to the next level.

Often times, car manfacturers will program the stock ECU with a known amount of “play”. This amount of play allows the manufacturer an extra level of safety and/or the ability to utilize this at a later date so they can have an increase in HP in later years. An example of this is where a 2001 car has 200HP and a 2002 car has 215HP. Some manufacturers couple this with additional parts to get increased HP levels, but this should give you some idea of the concept. From a marketing and sales aspect, this ensures that the public will continually be interested in the new year models, even if the body style does not change. While this FAQ is not about the science and art of auto sales, this may give you an insight as to why the stock ECU is not 100% perfectly tuned from the factory.

What are the least talked about benefits of engine management? Engine management solutions to one degree or another can reduce or eliminate black tailpipes, improve drivability throughout the powerband, eliminate the open/closed loop delay in 04+ Subarus, and increase MPG.

What Subarus NEED engine management? While every Subaru will benefit from engine management, the 04+ turbo models (except STI) "require" it. The reason for this is the EPA mandated greater restrictions on ECUs for 2004+ and allow manufacturers to exclude one model. Subaru chose the STI as the exclusion, so the restrictions are not on the STI. The restrictions have to do with the open and closed loop fueling. To put the restrictions in a nutshell without being technical, there is a delay between open and closed loop fueling that can allow your 04+ Subaru to run lean during this crossover point in how your car gets fuel. Lean is dangerous as it produces detonation which is the #1 factor is blown pistons. In stock configuration, 04+ turbo models are fine, but modifications such as exhaust work or higher really necessitate the use of engine management as those mods cause the fueling issue to rear it's head. Yes, you can run certain mods for a short time until you get engine management, but you should never kid yourself on 04+ turbo models that bolt on modifications are fine without engine management.

What about manual/electronic boost controllers or air fuel controllers?
A manual/electronic boost controller or air fuel controller really isn't engine management. MBCs are fine when used correctly on 02/03 WRX and 04+ STI by a judicious user. The issue gets further clouded on 04+ turbo models less STI, due to the open/closed loop delay. One can lump in the mix air/fuel controllers as well for the same reason. Usually those two devices are used by either cheap skates, n00bs, or advanced users who combine them with other forms of real engine management.

What types of engine management solutions are available? They fall into one of these general categories:
a. Reflashed ECU
b. Custom Tuned ECU
c. Piggyback Engine Management
d. Stand Alone Engine Management
e. Open Source Engine Management

Reflashed off the shelf ECU: This is your stock ECU that has had the programming modified. This form of engine management is best suited for people who:
a. Have a “set it and forget it” attitude towards engine management
b. Live in remote areas and do not have easy access to a tuner
c. Do not want to learn or are uneasy doing their own tuning
d. Want to modify their vehicle to a certain level and quit or add parts very infrequently

It is important to note that while reflashed ECUs are considered a static engine management option, they can be custom tuned by the end user by utilizing additional add-ons from the manufacturer or via a custom tuned reflash by an authorized tuner.

In addition, also consider that EcuTek tuners might have reflashes for your exact equipment set-up based on their prior custom tunes. This means that someone who has a full TBE might find the Cobb AccessPort a better plug and play solution, while someone with a full TBE, uppipe, headers, & a lightweight pulley may find an EcuTek reflash a better plug and play solution if they can find an EcuTek tuner with that exact map.

Recently for AccessPORT users, "custom maps" have become vogue. These come in the form of more specific maps for specific mods. Let say you have a stage 2 car with headers, TGV deletes, and a pulley. You email this information to a tuner and they will create a custom map for those mods to use. Some will send you a map and logging software, you load the map and data log, then the tuner sends you a final customized tune. While not as perfect as an in-person/on-dyno custom tune, it's a great resource for those in areas without tuners. Companies that do this are PDX Tuning, Perrin, and Clark Turner.

Examples of reflashed ECUs are the Cobb AccessPort and EcuTek (including Prodrive’s PPP & Vishnu’s reflash).

Reflashed custom tuned ECU: This is the next evolution to a reflashed ECU. This allows either the end user or a professional tuner to custom tune your vehicle to your specific modifications, wants and desires, type of gasoline used, and geographic area. This form of engine management is best suited for people who:
a. Will probably modify their vehicle frequently and require additional tuning
b. People with the ability to do their own tuning
c. People that live close to a tuner
d. People that want to get the maximum power and safety out of their car

Examples of Custom Tuned ECUs are Cobb Tuning’s StreetTUNER for end user tuning, Cobb Tuning’s ProTuner for professional custom tunes, EcuTek custom tune via an EcuTek tuner, and EcuTek's DeltaDash Live User Tuning, an end user tuning solution.

Piggyback Engine Management: This is an engine management option that works in conjunction with your stock ECU. Depending on the manufacturer, this solution works by the piggyback unit controlling some engine management functions and the stock ECU controlling others. This form of engine management is best suited for people who:
a. Will probably modify their vehicle frequently and require additional tuning
b. People with the ability to do their own tuning
c. People that live close to a tuner
d. People that want to get the maximum power and safety out of their car

It is important to mention that most piggyback units come with base maps. These base maps work very similar in function to a reflashed ECU whereas you can run the base map and be 100% fine, or when the day comes for someone to tune their own car or have it professionally tuned, they may do so.

Examples of Piggyback Engine Management are Unichip, Xede, UTEC, and others.

Stand Alone Engine Management: This is an engine management solution that totally replaces the stock ECU and controls 100% of the engine’s functions. This form of engine management is best suited for people who:
a. Will probably modify their vehicle frequently and require additional tuning
b. People with the ability to do their own tuning
c. People that live close to a tuner
d. People that want to get the maximum power and safety out of their car

This form of engine management is generally reserved for more advanced users and people going for really high levels of performance.

It is important to mention that most stand alone systems do come with base maps. Unlike the base maps that come on reflashed ECUs, these base maps are meant for your vehicle to run for a short period of time and are not meant to be used as a permanent solution as is the case with the other base maps as described above. Consider these base maps as merely as short term option until end user or a professional tuning.

Examples of stand alone engine management are MoTeC, Hydra, AEM, and others.

Open Source Engine Management: This can be the cheapest source of engine management available. In essence, you use a laptop, software, and a cable to reflash your stock ECU. Can be used to flash "staged maps" as a set it and forget it option or as a dynamic tuning tool either through tuners or by the end user. This form of engine management is best suited for people who:

Group 1:
A. Already have a good degree of tuning knowledge and understand the logic of the factory ECU (or have a strong desire to learn both).
B. Want to constantly tweak and experiment with their own tune. They actually enjoy the process.
C. May be changing/upgrading mods frequently.

Group 2:
A. Looking to get a custom tune from a professional but cannot afford or do not want to spend the money on license fees and/or hardware costs required of Cobb, Ecutek, etc. That is, they want their car to have a custom tune from a pro at the least cost. More and more professional shops are offering open source tunes and they can be just as capable as tunes from the commercial software.
B. Want an inexpensive (ex. XPT) or free (created by another user) OTS map. Might not go with EM otherwise because they feel it is too expensive. They are willing to learn the basics of logging with RomRaider to make sure the tune doesn't have any issues with their car.

Those people where Open Source Engine Management would be a BAD choice (assuming they are doing it themselves and not a professional tuner):
1. Want the easiest to use, troubleshoot, and closest thing to "set and forget" EM solution.
2. Are computer illiterate.

Examples of Open Source Engine Management are RomRaider, formerly known as Enginuity, EcuFlash, and others.

Can the dealer detect my reflashed ECU (AccessPort/EcuTek/Open Source)?

YES the checksum of the ECU changes.
YES the dealer can easily read the checksum.

NO the dealer has nothing to compare the checksum against there are many revisions of the WRX ecu they all have different checksums. If the dealer had someway of putting this checksum into a database he COULD verify that the code had been modified but at this time he doesn't.

The 05+ ECU and some of the 04s have the VIN in the ECU code. The current versions of reflashed ECUs only change the tables so the VIN will report when queried.

Bottom line: If you don't want modifications to be detected, don't modify the car.

What are some specific types of engine management While this FAQ does not go into specifics for every type of engine management, this thread covers many types. This link offers several comparisons of different system features as well. There are some not covered in these threads though and may be considered as well.

Generally speaking, what engine management option will give me the most power? Custom tuned engine management solutions will always give you more power. Every off the shelf engine management solution has a built in safety factor. This depends on the manufacturer. This is because their “Stage 1” or “VF-30” map has to safely make power for someone living in Phoenix’s heat and 91 octane, to Denver’s high altitude, to Boston’s cold and 93 octane. The gasoline and geographic variances can leave horsepower on the table.

More specifically, what engine management option will give me the most power? This is one question without a correct answer. Let’s say that you research a very comprehensive stand alone engine management system such as a MoTeC unit and decide that it’s the “best” for your car. At the end of the day, it’s about what the tuner is most comfortable with. Some tuners may be able to extract better results from a “lesser” system simply because they understand the interface better.

For someone interested in tuning their own vehicle, they should match their tuning skills with an engine management solution that they are able to understand and use correctly. For someone interested in professional tuning, they should consult with their tuner for their recommendations. Both of these actions will ensure a good tune with a minimum amount of rework, guessing, and trial and error. While most tuners are capable of learning new or more advanced engine management systems, consider the benefits of an “older/worse system” your tuner is familiar with vs. your tuner learning a “newer/better system” at $200/hour plus possible dyno time.

I have a reflashed ECU and am not seeing their advertised HP, why? First off, have you met their criteria EXACTLY? The #1 cause of low HP with reflashed ECU owners is their lack of meeting the manufacturer’s requirements. If they require a full turbo back exhaust and you only have a downpipe and a cat back exhaust, 100% of the blame is on the end user. As well, if they require a full exhaust and you have a full exhaust, uppipe, headers, and a bigger top mount intercooler, this can cause problems as well.

Also realize that HP figures vary. You cannot compare (for example) a manufacturer’s Mustang Dyno HP figures to your local DynoJet HP figures. Even comparing identical dynos to each other is futile as dyno software set-up, altitude, temperature, humidity, and other factors do not ensure an equal result.

In addition, realize that a reflashed ECU still utilizes many of the stock ECU’s learning functions. This means that in a perfect world, you will see the advertised HP from your reflashed ECU. This may also mean that on the day of dyno testing, your octane, the temperature, humidity, and many other factors are considered by the reflashed ECU when determining total power output. If the advertised numbers aren't there on dyno day, it doesn’t necessarily mean there is a problem, but rather, your ECU is protecting your engine from low octane, high temperature, high humidity, or other factors.

How much is a custom tune by a professional? Expect to pay $100-$150 per hour for the dyno time. Your tuner’s fee depends on their level of experience and pricing. Tuners generally charge $100-200 per hour for their time. The amount of total tuning time depends on the tuner and the amount of time you wish for them to tune your vehicle. Most tuners can get your vehicle within 90-95% of its maximum power within 1-2 hours.