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Old 04-01-2018, 03:34 PM   #1
ummwhat
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Default A lot of questions about what to expect

Hi,
I keep reading people say that the stock tune on WRX is 'terrible', and that OTS maps are much better, but most people only comment on improved power and smoother torque curve. However I'm curious about a number of effects:

MPG - I've read that ECU tuning 'can' improve MPG, but there doesn't seem to be much info on why, and whether you can get both improved power and MPG or if it's a tradeoff between the two?

Emissions - Typically people who want performance don't care about emissions (or they'd have bought a prius). I imagine this is related to MPG above, but what impact does tuning have on emissions? I've heard that it helps eliminate rev hang for MT, but my understanding is that rev hang is to reduce emissions caused by sudden changes in throttle, so I'm wondering if there are other similar tradeoffs made that will make me feel guilty of killing baby birds if I get a reflash?

Margins - My understanding is that the stock tune is set for the lowest common denominator to run safely in all conditions, and lower "stage" OTS maps (i.e. stage 1 cobb) are similarly conservative but less so. Is there just insane overkill in the stock tune's "safety factor" or is there some risk of OTS tunes causing problems in harsher conditions? Am I going to need to forever be monitoring/logging to make sure my engine doesn't blow up unexpectedly if I take a road trip through the desert or into the mountains?

Wear - Any concerns with shortening the lifetime of surrounding components (in particular CVT) or is there plenty of headroom in their designed capabilities for whatever power gains you might make from an ECU tune?

Hardware - Searching for "Cobb stage 1" points me at their package with AP + air intake. Is the air intake actually necessary or would I benefit from the flatter power curve and get some marginal gains with ONLY an ECU flash? Would it throw things off and cause other issues since it was expecting a modded intake?

Other ECU stuff - Does the AP just tweak some numbers and parameters, or is it reprogramming the whole ECU's control logic? If the latter, is that risky? e.g. if the manufacturer had some design issue that they "solved" by hacking some workaround into the ECU, and by overwriting the ECU programming we delete that workaround and expose ourselves to a hidden problem?


I'm pretty newb about all of this but would love to learn, so thanks for your patience!
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Old 04-01-2018, 04:47 PM   #2
Blktrax
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Simply put , if you are concerned about MPG, you bought the wrong car. You will never recover the $600+ to justify the accessport for 1-2 mpg

Second, as power increases longevity decreases ,along with the risk of warranty denials due to the ECU being modified.

Drive it like it is, or modify it to the moon, you pay to play, just donít gripe when it breaks.
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Old 04-01-2018, 05:22 PM   #3
ummwhat
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Thanks for the response. Of course I'm not trying to recoup money through mpg improvements. But I do want to know what impact to expect - better, worse, no change, or "it depends what you change when tuning". There are practical implications on range etc. as well as just generally being curious about the answer as there doesn't seem to be much info about it.

And yes, thank you for the vague generality about power increasing wear. I am more interested in differences on the scale of "it would have lasted 200k miles just fine but now it will fail catastrophically in 20k miles because the CVT can barely handle the stock power", and specifically with regard to the smaller power gains from only an ECU flash and no other modifications.
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Old 04-01-2018, 05:46 PM   #4
JavelinGuy
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The stock tune is fine, emissions and MPG are not directly related and power will in general decrease the life of your engine or components. All of these are general statements and things have to get more specific, IIRC the cobb stage 1 is just a air filter and access port there is very little damage that an air filter can do. A bad tune can damage the engine or other components, get a good tune done and you'll be fine. MPG can be helped by a tune but you'll have to tune it for it, normally this does take away from power.
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Old 04-01-2018, 07:54 PM   #5
mrsaturn7085
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Quote:
Originally Posted by ummwhat View Post
MPG - I've read that ECU tuning 'can' improve MPG, but there doesn't seem to be much info on why, and whether you can get both improved power and MPG or if it's a tradeoff between the two?
You might be able to improve MPG... but it will be difficult to do better than OEM. Boxer engines (particularly turbo boxer engines) use extra fuel to aid in charge cooling - you really didn't buy the right car if you want fuel economy.

Quote:
Originally Posted by ummwhat View Post
Emissions
I *HIGHLY* doubt you will do better than OEM here, and you will need to probably buy your own testing equipment if you're trying to tune for this on a dyno at a performance shop.

Fuel economy, performance, and emissions are a balance in tuning. Performance tuning usually ignores emissions and gives up a little economy for a little performance. Safety and performance is another different, but related balance.

Quote:
Originally Posted by ummwhat View Post
Margins - My understanding is that the stock tune is set for the lowest common denominator to run safely in all conditions, and lower "stage" OTS maps (i.e. stage 1 cobb) are similarly conservative but less so. Is there just insane overkill in the stock tune's "safety factor" or is there some risk of OTS tunes causing problems in harsher conditions? Am I going to need to forever be monitoring/logging to make sure my engine doesn't blow up unexpectedly if I take a road trip through the desert or into the mountains?
This isn't really true - OEM maps still use dynamic ignition timing to maximize performance within limits set by the maps.

OTS base maps generally bump boost a little, lean out the loaded portion of the fuel map, and sometimes tweak AVCS settings. That's about it.

The only 'lowest common denominator' part of an OEM tune is the excessively rich high-load area of the fuel map. This is extremely common on all OEM turbo cars.

Quote:
Originally Posted by ummwhat View Post
Wear - Any concerns with shortening the lifetime of surrounding components (in particular CVT) or is there plenty of headroom in their designed capabilities for whatever power gains you might make from an ECU tune?
If you run rich (as many tunes tend to), your oil life will decrease. You absolutely, positively MUST keep on top of oil changes.

Quote:
Originally Posted by ummwhat View Post
Hardware - Searching for "Cobb stage 1" points me at their package with AP + air intake. Is the air intake actually necessary or would I benefit from the flatter power curve and get some marginal gains with ONLY an ECU flash? Would it throw things off and cause other issues since it was expecting a modded intake?
On these MAF-based algorithms, you usually want to stick with an intake when a tune tells you to use an intake. If you ever switch to speed density, it's a different story... but you probably won't be using a base map then.

Quote:
Originally Posted by ummwhat View Post
Other ECU stuff - Does the AP just tweak some numbers and parameters, or is it reprogramming the whole ECU's control logic? If the latter, is that risky? e.g. if the manufacturer had some design issue that they "solved" by hacking some workaround into the ECU, and by overwriting the ECU programming we delete that workaround and expose ourselves to a hidden problem?
The AP is reflashing the internal tables, basically. It *is* actually changing firmware to allow the AP to communicate with the ECU itself... it's difficult to explain in more detail unless you have a background in microcontroller/firmware tinkering. When you get into speed density conversions, you're effectively re-writing the firmware with a hacked-up version that combines the original code from your ECU with that of a GpN ROM that STI sold.

Last edited by mrsaturn7085; 04-01-2018 at 07:59 PM.
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Old 04-03-2018, 11:10 PM   #6
ummwhat
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Thanks for the detailed response! This is helpful.

Although I'm starting to think that I should just take a class in tuning to learn the how and why of things instead of posting random questions and googling. I wonder if there are any colleges around here that teach this stuff...
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Old 04-14-2018, 09:48 AM   #7
cerbomark
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I did a stage 1 91 OTS Cobb and am happy with the driveabilty and not looking for big power gains. My research finds it s safe and I am getting higher MPGs. I also have found that understanding the tuning world deeply will require more than a few classes.
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Old 04-16-2018, 11:58 AM   #8
Sw20matt
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Quote:
Originally Posted by ummwhat View Post
Thanks for the detailed response! This is helpful.

Although I'm starting to think that I should just take a class in tuning to learn the how and why of things instead of posting random questions and googling. I wonder if there are any colleges around here that teach this stuff...
there is a lot of info out there that you can access for free. if you dont mind a lot of reading and research than you can learn to tune the car yourself or at least have an understanding of why an intake on an untuned car is so bad and other things along those lines.
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