Yes, you need an EM for engine mods
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This is a discussion on Yes, you need an EM for engine mods within the Tuning: Electronic Engine Management forums, part of the Tech & Modifying & General Repairs category; I've noticed quite a few questions regading the necessity of an Engine Management system (EM), based upon certain upgrades. Rather ...

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    "Supreme Subaphile Extraordinairre" ninefourteener's Avatar
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    Yes, you need an EM for engine mods

    I've noticed quite a few questions regading the necessity of an Engine Management system (EM), based upon certain upgrades. Rather than searching in 27 different threads to find out, I'm going to try to create an all-inclusive thread.

    With that, I'm going to (hopefully) clear up any misconceptions...

    1) A catback exhaust (CBE) does almost nothing for your car except make it sound cooler.... you do not need an EM

    2) An aftermarket intake "can" cause your car to run lean (too much air, not enough fuel)... so yes, you should be tuned. The exception would be an SPT intake, as Subaru claims they are safe to run on the stock engine/ECU. However, I would get tuned anyway.

    3) A Turboback exhaust (TBE) includes a bellmouth Downpipe (DP). The DP allows your turbo to boost higher, and produce more power. With that, if your ECU is not telling your injectors to supply more fuel, and adjust the timing, to compensate for the added boost.... then once again, lean conditions and boost spiking occur. Yes, you need an EM.... period

    *** Note, if you have a downpipe with no EM, don't complain when you blow something up.

    4) An aftermarket top-mount intercooler (TMIC) with do very little for your performance... it will however, give you greater protection from heatsoak. No, you do not need a tune.

    5) An aftermarket front-mount intercooler (FMIC) gives you added protection from heatsoak, but because the forced air has so much further to travel, it has been known to cause a bit of added turbo lag. The general rule of conscensus is that you don't need one unless you are over 350 whp. If you choose to use one anyway, then yes, you should be tuned.

    5) a BOV will do NOTHING for you.. at all. In fact, if you don't get a recirculating BOV, you'll probably end up hurting your performance. Either way, you do not need a tune to install one.

    6) On pre-06 WRXs, an aftermarket catless uppipe will give you added performance, and in many folks' eyes, is necessary preventative maintenance to ensure the catalytic converter doesn't get sucked up into the turbo. It will allow your turbo to spool up quicker, but generally will not cause lean conditions or boost spiking. For an uppipe only, no, you do not need a tune.

    7) lightweight pulleys are the equivilent of removing weight from your car, you do not need a tune.

    8) Turbo upgrades..... whatever it is, yes, you need to be tuned.... I can't tell you how many stock WRXs I've seen that bolt on a VF39, an 18G or a 16G turbo and drive off without doing anything else...... then complain about why their car doesn't run right.

    Please... if you have anything else to add.... please do. Just seems like we get a lot of the same questions over and over again.... trying to help here and steer people in the right direction.

    An EM should be the VERY FIRST item you buy for your car.... and I think just about everyone will agree with me on that one. Yes, they are expensive... but you only have to buy it once, it's infinately upgradeable, and most importantly, it's SAFE.

    Hope this helps.
    Last edited by Rogan; 04-23-2009 at 09:44 PM. Reason: changing title to something less aggressive
    2006 Subaru WRX-Thread: http://www.clubwrx.net/forums/engine-modifications/165158-ninfourteeners-progress-thread-pics.html
    1978 Subaru BRAT-Thread: http://www.clubwrx.net/forums/engine...ss-thread.html
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    Registered User Timdog1650's Avatar
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    If you edit the first paragraph to be a bit more user friendly and less abrasive, I think this would be worthy of being stickied...

    Things I would include

    Exhaust manifold/header: No, you do not need EM but you will realize better performance gains if you are custom tuned to account for this mod

    Turbo Port/Polish:
    No, not necessary. This, much like a catless uppipe, will simply increase the efficiency of the system, not necessarily a huge increase in performance. While this mod will certainly change the dynamics of your turbo system, it will not be outside the safe control of the stock ECU.

    TGV deletes:
    Yes, you need EM to delete the inevitable CEL that will result from deleting your TGV's and you need some way to tune for the increased airflow across the RPM range

    Boost controller, manual or otherwise:
    Yes, kind of. Any time you raise boost more than 2 psi on an otherwise mostly stock car, you should add engine management. The argument could be made that 2 psi increase or less is not going to do a whole lot to hurt you. That being said, you should not be increasing boost without aftermarket exhaust, and you should not have aftermarket exhaust without EM, therefore by the transitive property, you should not have a boost controller without EM.

    Turbo inlet hose/any pressurized post-turbo piping or hoses: Absolutely not, these do very little to change the performance of the car and really only help making the turbo parts easier to remove/install.

    Walbro Fuel pump: No, your fuel pressure regulator prevents a higher volume pump from overpowering the injectors and thereby altering fueling. If you change your fuel pressure regulator in any way, you will need to account for that change via tuning, but an otherwise drop-in Walbro replacement does not need EM.

    Larger than stock injectors: Yes, you definitely need to tune for larger than stock injectors. A car will start with over-sized injectors and will likely drive "okay" but will not run properly and will be way too rich to drive aggressively.

    Fuel Rails: No. See discussion of Walbro pump. More potential flow to the injectors does not necessarily mean your injector will inject more fuel unless you tell it to. Very minor tweaks may be needed if you do this mod, so minor you would probably never notice them and they would do no damage.


    AccessPort vs OpenECU/RomRaider/Enginuity/Tactrix: Yes, AP is the easiest and most reliable way to modify your stock computer. The "DIY reflashes" are also very good and much cheaper. If you think you are going to need engine management, do not immediately discredit the DIY methods. With proper education, patience, and a careful and inquisitive mind, flashing a stage 2 car yourself is reasonably safe and easy to do. Making the choice to do it yourself is basically a measure of how confident you are that you can follow carefully outlined procedures and use good common sense to troubleshoot a problem if something goes wrong. The Cobb AP is basically idiot proof, but you have to pay for this feature, as well as their customer support.
    Last edited by Timdog1650; 05-26-2008 at 01:12 PM.

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    "Supreme Subaphile Extraordinairre" ninefourteener's Avatar
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    Quote Originally Posted by Timdog1650 View Post
    If you edit the first paragraph to be a bit more user friendly and less abrasive, I think this would be worthy of being stickied...
    You're right... didn't mean to come across like that at all.

    I changed it... I think it sounds more PC
    2006 Subaru WRX-Thread: http://www.clubwrx.net/forums/showthread.php?t=165158
    1978 Subaru BRAT-Thread: http://www.clubwrx.net/forums/engine...ss-thread.html
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    WRX track racing (catching a stg.2 WRX): http://www.youtube.com/watch?v=mELeSD1Mi08
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    Registered User Timdog1650's Avatar
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    Quote Originally Posted by ninefourteener View Post
    You're right... didn't mean to come across like that at all.

    I changed it... I think it sounds more PC

    Good stuff, I'm gonna report this to the forum mods and see if they can throw it in the stickies.

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    Weasel 555's Avatar
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    how about i put it in the Electronic Engine Management thread

    plus i want to delete the AP port , its definitely not the most reliable
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    Registered User Timdog1650's Avatar
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    Quote Originally Posted by Weasel 555 View Post
    how about i put it in the Electronic Engine Management thread
    That works, would it be too much to ask for both since they're inter-related?

    Quote Originally Posted by Weasel 555 View Post
    plus i want to delete the AP port , its definitely not the most reliable
    I guess it's a matter of opinion, but it certainly does what it's intended to and has a solid track record. What would be your pick for "most reliable?"

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    Registered User Micah's Avatar
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    Quote Originally Posted by Weasel 555 View Post

    plus i want to delete the AP port , its definitely not the most economical
    fixed?
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    Geriatric Ginger Mod Rogan's Avatar
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    I'm actually working on a thread sticky/addition/whatever, offline, that will be posted up soon.
    But yeah, I concur on the merge.
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    Registered User tmann05's Avatar
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    sticky this biotch...ill be reading this often...of course when i do get an STI
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    Moderator Donkey's Avatar
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    Quote Originally Posted by ninefourteener View Post



    4) An aftermarket top-mount intercooler (TMIC) with do very little for your performance... it will however, give you greater protection from heatsoak. No, you do not need a tune.
    Okay.You replace the stock tube and fin TMIC with a bar and plate TMIC of close to similar size.Now you have gone from a 2psi pressure drop to a .5 psi pressure drop.That means you are now overboosting by 1.5psi or maybe more depending on how the stock temp compensation can correct plus probabaly over running the stock load mapping.A tune would be a good idea for the same reasons as a TBE except now the pressure differential is on the intake side.Plus tuning for a more efficient TMIC allows you to run more boost and more timing advance with leaner AFR's.Also you have 2 #5's
    Last edited by Donkey; 05-10-2008 at 11:40 AM.
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  12. #11
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    Moved over to EM for the time being as it seems more "fitting" in that forum.


    Good info in here.
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    Registered User FlimFlamMan's Avatar
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    Good info.. and a quick read (not 5 miles long).
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    Moderator timber's Avatar
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    I'll throw one out there, what with fuel prices being what they are..

    Higher Than Recommended Octane Fuel: Don't waste your money on higher than recommended octane fuel, as your car cannot take advantage of it unless you are tuned for it.
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    Registered User 05wrxftw!'s Avatar
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    Quote Originally Posted by ninefourteener View Post
    You're right... didn't mean to come across like that at all.

    I changed it... I think it sounds more PC
    lol it was kinda "mean" but screw that......


    people need to know whats what. i tell people straight up what they should/should not get, do or buy.

    lol. i say Cobb AP is hands down the best bang for the buck. IMHO

  16. #15
    Geriatric Ginger Mod Rogan's Avatar
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    telling them what they should/shouldn't buy, is opinionated.

    your and my opinions differ. you enjoy Cobb, and I prefer RomRaider.

    90$ vs. 600$.

    $600 buys me EMS and 510$ of other go-fast goodies.

    Again, though, opinionated.
    Rogan o_0
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