New to Subaru turbo tuning questions.

[DDMan]

I've read up about all the tuning forms and whatnot but there is still one thing that gets me. WHY is tuning so important when small parts are changed?

 

I'm coming from the Audi 1.8T world where you got a flash when you upgraded your injectors, another when you upgraded your turbo, and really..that's about it. You could change from a 91 octane to a stock map and set the boost level using a computer plugged into the OBD port. You could add intakes, cat back, turbo back, headers....it didn't matter. You just felt the power in your butt.

 

Now I come over to Turbo Subarus and you touch anything performance wise on the car and you need a tune. WHY?! I've owned a 2002 2.5RS since it was brand new in 2001 and I added exhaust, headers, intake and didn't need a tune with that (although a refresh is my next mod). Are the ECU's so dumb they can't learn minor changes to the airflow? I mean EVERYONE says you need a tune with a downpipe. They talk about boost creep, boost spikes, running lean and frying pistons... I find it incredible that a ECU made in 2005 are newer is unable to compensate for such minor (airflow only) modifications. Makes me thing if I ported and polished a set of heads I would need a tune!

 

So please, can someone explain to me why this is?! Thanks in advance.

[Ridgeracer]

Well I am not sure about an Audi 1.8T motor but when you change the MAF housing on any MAF sensor based car, you need to rescale the MAF. In CL operation, depending on how much up/down compensation there is built in, this is not a problem. The problem arises when you are running OL. Some cars run a conservative primary open loop fuel table so you have some safety here. Some aren't so forgiving. Turbo Subarus come stock with a lot of restrictions (i.e. cats) in the exhaust systems. When you start changing downpipes and CBEs the flow throught the engine and turbo increases. Depending on how much of an increase you have, you may or may not have issues with boost control.

[B-BGTLimited]

To be a bit more simple of an explination... the boost is controlled electronically, and it expects or knows of a certain amount of restriction in the exhaust, if you free that up thats not a table that auto adjusts, so yes you will over boost, boost creep or spike... With something older that may have had a different setup for boost control it may be able to compensate for those changes since its a mechanical function rather than electronic.

 

In reality you can just do whatever you want, but you will not see the full potential of the part your installing without a supporting tune, and you can possibly hurt your motor if you do not monitor/change things regarding fueling. You can go all day long not knowing your lean and knocking until you check it with a computer or months down the line something finally fails, but during that time you "thought" it was perfectly fine... Depending on what you had done to your RS you might not have ever checked to see what the ECU was saying and you could have been missing out on so much more power.

 

I did a stage 2 setup on my car and did a stage 2 tune, and the tune was made for simply a gutted stock cat, I put on a 3" bell mouth catless downpipe and full CBE, so I had NO cat's in my system anymore... and needless to say I was hitting the boots limit which was set at 18.4. My boost target was 17 at the time, so that shows you how much you can over spike if your ECU doesn't agree with what you have done.

[DDMan]

Okay well that makes some sense. I don't plan on changing the MAF or anything like that. I was under the impression that there was enough "play" in the stock tune to allow for the decreased intake/exhaust restrictions. Guess it doesn't take much to Max out the stock ECU. That I guess is the difference between the Audi and Subaru. Its more adaptable and accepts a larger range of flow through the motor. Stock boost is 8psi and I'm currently running 21psi on a bone stock motor. In the Audi world that is fine though.

 

As for my RS I race the car and have never had a problem with pinging, knocking, cell's....all with the stock tune. Guess well see what happens when I send in the ECU for a reflash.

[B-BGTLimited]

Do you have an FMU or manual boost controller on the Audi?

[GTTuner]

Okay well that makes some sense. I don't plan on changing the MAF or anything like that. I was under the impression that there was enough "play" in the stock tune to allow for the decreased intake/exhaust restrictions. Guess it doesn't take much to Max out the stock ECU. That I guess is the difference between the Audi and Subaru. Its more adaptable and accepts a larger range of flow through the motor. Stock boost is 8psi and I'm currently running 21psi on a bone stock motor. In the Audi world that is fine though.

 

As for my RS I race the car and have never had a problem with pinging, knocking, cell's....all with the stock tune. Guess well see what happens when I send in the ECU for a reflash.

 

Subaru motors are not as forgiving as say and Audi or a Saab 4cyl. I see SRT-4 kids running 21psi on a stock tune.

[DDMan]

Do you have an FMU or manual boost controller on the Audi?

 

Boost is controlled electronically. When I plug my computer in I can change the max boost. Its all part of the GIAC software.

[B-BGTLimited]

And therefore you've tuned it.... I'm confused now, you made it sound like you just bolted parts to the audi and changed nothing with the computer or any computer for that matter but you have. So why are you surprised you need to adjust the ECU of the subaru?

[DDMan]

And therefore you've tuned it.... I'm confused now, you made it sound like you just bolted parts to the audi and changed nothing with the computer or any computer for that matter but you have. So why are you surprised you need to adjust the ECU of the subaru?

 

I'm surprised it's pretty much REQUIRED. I could bolt up a new intake, and exhaust to the Audi, and as long as the mechanical or sensor parts of the car are stock (turbo, injectors, fuel pump, MAF, internals) you don't need a tune. The car is able to adapt to the increased airflow fine. My N/A Subaru seems to do the same, however the increased flow from the bolt on parts for the N/A motor is probably ALOT less percentage wise than a comparable turbo, and the N/A ECU seems to be able to work with it.

 

However, since I replaced the turbo and injectors on my Audi, I had to get a tune that had recalibrated to those new parts. The tune did not require any additional mods. Me adding a FMIC, turbo back, and (if I wanted to) an intake did NOT require a new tune.

 

What I'm confused/surprised with is the NEED for a tune with simple bolt on mods like the intercooler, intake, and turbo back exhaust. It was pretty well explained above and it has to do with the stock map not being able to compensate for the significant increase in airflow to the motor. That was my primary question, and it also answers WHY people fry their motor when they don't get a tune.

 

When you greatly increase the airflow, you need more fuel. If the car doesn't have a map for that increased airflow, it will reach a point where it's at it's upper limit for fuel delivery. When you flow more air than the amount of fuel you have you run lean, increase EGT's, and fry the motor. That's why you CAN drive the car for short/leisurely distances without a tune, however just opening it up once CAN boost spike, increase EGT's, knock, run lean, and cause damage.

[Mortal2None]

I don't think it's an apples to apples comparison when talking about a N/A Subaru and one with forced induction. The N/A engine/ecu is dealing with 14.7PSI at sea level and it only changes with altitude and barometric pressure. The turbocharged engine is dealing with many more variables and therefore the room for error can be fairly small at low pressures and razor thin at higher ones hence the "need" for a tune.

[SeeeeeYa]

If one's goal is to work on a Chevy one should have the Chevy manual on hand... not a Saab manual, and a notebook full of their differences.

 

When I work on my TWO horsepower-per-cubic-inch Subaru, stock, I tend to pay close attention to what the engineers gave me to work with. That has never included researching Audi forums for input. Nor does it include researching Mustang forums, although my background was forged from big and small normally aspirated engines, one of which was a Buick. And while Buick has, and again does, produce turbo cars I haven't once researched the Buick database for ideas relative to my Subarus.

 

The Tuning Forum is for people interested in tuning a Subaru, not a general forum for esoteric inquiry into the "why" of tuning. Google is good for that.

 

Once you understand what tuning actually is, and does, questions will be easier to answer... if they are about a Subaru turbo H4.

[B-BGTLimited]

My question is has this been documented and proved via a datalog of a car, or is it just "it's running fine" statement thats made this "true"

 

. I could bolt up a new intake, and exhaust to the Audi, and as long as the mechanical or sensor parts of the car are stock (turbo, injectors, fuel pump, MAF, internals) you don't need a tune. The car is able to adapt to the increased airflow fine. My N/A Subaru seems to do the same

 

Without dataloging the ecu then you have no idea what is going on and can't make any conclusions about necessity of a tune.

[DDMan]

I haven't datalogged my Subaru, but I HAVE datalogged my Audi (on the road, not a dyno), and yes, things are running fine. The HEX+CAN Ross-tech cable plus my laptop have been invaluable in solving problems and making sure the car has been daily-driven reliable despite being about 70+ HP from stock.

 

There really aren't many options for tuning my N/A Subaru. On that note, I don't think I've ever read or been told that tuning is a REQUIREMENT when you're helping the engine breathe better (simple, bold on mods).

 

I'm sorry if I compared the method of tuning one small displacement turbo motor to another from a different manufacturer. Or a N/A motor vs a turbo from the same manufacturer. I only used them because their ECU's seemed to adapt to changes fine. I do however understand the additional complexity of running/tuning a turbo motor, and the need for some additional "horsepower" in the ECU to make those calculations.

 

When tuning a car, methods and software may be different, but in the end you're still looking at similar, specific parameters to make sure the car will run how you want it to (max performance, reliability, fuel economy, etc).

 

The purpose of this thread was to find out more about Subaru turbo tuning. My only tuning experience has been with the Audi and so that's what I compared it to. I just wanted to know WHY people say its a requirement to get a tune for the Legacy GT motor with simple bolt-on's (not just recommended, but the motor can go boom if you don't). In my limited research, I was unable to find the answer, so I figured I would come to the source.... the TUNERS. You guys are the ones who know what is dangerous and what isn't when it comes to these motors.

[B-BGTLimited]

I haven't datalogged my Subaru, but I HAVE datalogged my Audi (on the road, not a dyno), and yes, things are running fine. The HEX+CAN Ross-tech cable plus my laptop have been invaluable in solving problems and making sure the car has been daily-driven reliable despite being about 70+ HP from stock.

 

Once again... Prior to the boost increase and everything? And were you monitoring A/F's?

 

I'm simply trying to debunk the statement that its ok with one car and not another because unless someone did full intake and exhaust mods and did full datalogs to see the engine running in optimal values and same exact boost levels then that statement of being able to do anything without a tune is a myth.

 

I also believe that a tune is "recommended"... Yes you will read it here a lot that it's "required" because if you don't say that too many people will skip the recommendation and typically that will not end well... At least wont if the user is hard on the car. Also with some of the new restrictions on the ECU's if you don't change it you will "over boost" according to the ecu, and constantly hit the fuel cut...

 

From my experience the things I see modified in the Stage 1 and Stage 2 tunes are mostly the limits, but at the same time since they are in there they take advantage of the other abilities of the mods or simply just the parameters they can change and increase the targets as well. The spark table doesn't HAVE to be changed but they make it a bit more aggressive, and honestly I have a CAI and I think I've scaled my MAF table by like 2-3%... which is piddly squat really, far from something that would blow my engine... and I'm still hitting 11.3-11.5 when in boost for a/f's. So really my "required" tune not only removed limits but bumped by boost from 13psi to 17psi. I can say that if I hadn't done the tune I think my only issue is I would be constantly hitting the boost cut due to the reduced restriction in the exhaust and the waste gate not being able to compensate for it, because of what it's expecting to be there.

 

I guess the moral of the story is, if you want to take full advantage of the modifications you are making to your car you need to let the ECU know they are there. And I think that applies to any and all makes.

[NSFW]

I'm surprised it's pretty much REQUIRED. I could bolt up a new intake, and exhaust to the Audi, and as long as the mechanical or sensor parts of the car are stock (turbo, injectors, fuel pump, MAF, internals) you don't need a tune.

 

With Subarus, the MAF sensor works in conjunction with the tubing around the MAF sensor itself. So, the MAF sensor signal depends very much on airflow though that tubing - it's very sensitive to changes in diameter and even to changes in bends in the tubing. And the MAF sensor is located in the intake. So, if you change intakes, you've changed the MAF sensor, and just like with Audis, when you change the MAF sensor you need to tune for that.

 

Some intakes are designed to keep the MAF signal consistent with the stock intake, but some aren't. Lots of them use larger diameter tubing, which causes the MAF voltage to be smaller for the same airflow, and the tune needs to be tweaked to accommodate that.

 

My N/A Subaru seems to do the same, however the increased flow from the bolt on parts for the N/A motor is probably ALOT less percentage wise than a comparable turbo, and the N/A ECU seems to be able to work with it.

 

The stock tune could probably cope with a 10% increase in airflow, which is probably about what you NA bolt-ons give you. But a catless up-pipe + high-flow-cat downpipe will let you increase the boost from 14 to 18-20 psi, and that will get you about 25% more airflow.

 

And the turbo itself is sensitive to changes in backpressure. As others have noted, if you upgrade the exhaust without tuning you're likely to develop enough extra boost to trigger the stock tune's self-defense mechanism, which is to cut fuel, which interrupts the fun. So at minimum you need to raise the fuel-cut boost limit.

 

And better yet you should retune the boost control tables because while the stock tune does have a feedback-based mechanism to cope with surprises, it's not flexible enough to deal with those sorts of exhaust upgrades. And besides, it will be targeting the stock boost levels, so it's going to bounce between the boost levels that it can reach (with upgrades) and the boost levels that its tuned for. It's not smooth and it leaves power on the table.

 

Plus there are plenty of threads here and at NASIOC with pictures of Subaru motors that have been destroyed by detonation. Maybe that's less common in the Audi world, but around here it's a constant reminder of how important it is to avoid knock. Maybe Audis are better at coping with upgrades, maybe Subaru pistons are just fragile, I really have no idea.

[DDMan]

BGTL: Before the boost increase, the car was stock, so there was no need to do any logging. The only mods I ever did were the turbo replacement (KO4 vs K03, same housing on both sides, just more efficient internal design), njectors, FMIC, and the cat delete pipe. I retained my stock exhaust and intake (aftermarket intake shows little to no gains before about 350HP, and I wanted to keep a "stealth" look/sounds so I kept the stock exhaust). I know I could have gained more power by getting a cat-back, but I wasn't worried about it. I installed the parts and actually took the ECU only to the shop where he reflashed the ECU and I went home and installed it and drove it. Took it easy during the break in and then after about 1000 miles I got on it more. Checked my A/F ratios, and compared my target vs actual boost. I was overboosting by about 1-2 PSI but the AFR's were fine. It was also not getting into the "dangerous" level for the engine (24~PSI) so I wasn't worried. It wasn't until a coilpack went out that I cut back the power to solve a misfire. Once the coilpack was replaced, power was restored and more logging was done to confirm it was running fine. No, I never used a wideband O2 sensor, just the stock one.

 

Definitely agree though that to take full advantage of mods you need to tune it properly.

 

NSFW: Makes sense about the MAF. As said above, Audi never had an aftermarket intake. I've heard with the LGT even a different FILTER can cause changes in the airflow and therefore issues with the MAF readings... My 2.5RS doesn't have a MAF, It's MAP, so I never ran into that issue there.

 

And sadly, yes I also agree with the motor toughness. The 1.8T's are considered pretty much "bulletproof" as are the transmissions. Difference between German vs Japanese engineering/manufacturing I guess.

[B-BGTLimited]

I have a hard time agreeing with what you've stated about how you tuned your car and the necessity of logging. Also if the stock sensor is anything like ours it is not accurate in boost since its pre turbo, also was the sensor you were using a factory wide band? or was it a narrow band? and where was its location.

 

My only example of this is when I get into boost my stock sensor is pegged at 11.2, doesn't budge... but my wide band which is post turbo reads 11.5-11.8 and sometimes 10.5 right when going into boost which the stock one wont recognize, so thats why I say relying on a stock component when you've modified things is a bad idea and it will not relay proper information.

 

I wont argue the toughness of certain engines because I just do not have enough knowledge about the Audi to say anything, I'm simply disagreeing with your tuning process and saying you would have benefited MUCH more if you were to tune it more and get your levels dialed in so it's responding exactly how the ecu expects... The biggest power robber is the ECU trying to compensate for something, Less correction equals a stronger smoother power band.

[DDMan]

My method of tuning was pretty much a non-method. I bought specific parts for a specific reflash and the other parts I got didn't matter. I only datalogged to make sure I wasn't going to blow anything up, not to change any aspect of the tune.

 

I was using the stock narrowband, however it is POST turbo. I understand the philosophy of proper tuning, but honestly...Audi's just aren't Dyno tuned on that often. People go to a dyno to get the power output. I don't think I've ever seen the type of software like the open source stuff seen here in the Audi world. It's all been "Accessport" style stuff where you plug it in, flash it, and you're done. I know they say that the AP Stage2 is decent, but there still is more power to be hand if you know what you're doing and get a full tune. That's why all this is so new to me. I understand if you're doing MAJOR changes to the engine (larger turbo, fuel, etc) that tuning is obviously mandatory, but for such small changes.... it seems crazy how "picky" cars can be when, just by changing an intake and downpipe and suddenly you're running the risk of trashing a motor.

 

It's all a learning experience, and I know that really, the car will be much better if its tuned to that specific car. Maybe that's why a simple chip for the Audi costs $500 just for a reflash, and you can do an e-tune for the Subaru for $150 or a full dyno tune for $500. Maybe that software has gone through so much testing and includes so many variables that you CAN change all that stuff out without any problems.

[NSFW]

Do the tools even exist for Audi? I mean, if you wanted to tune your Audi yourself rather than buying a reflash, could you buy the hardware and software, at any price? If so, how many vendors are there?

 

Even in the Subaru universe, Cobb tuners charged more before EcuFlash/RomRaider caught on as a tuning system. When that happened, the number of tuners went way up, and prices went way down.

[Sicotic]

is there a thread about using ecuflash and rom raider? where do i get the cable?

[DDMan]

NFSW: The logging tools are available. As for tuners... there were some but I never looked into how they "tune" a car because they were always talking about BT (Big Turbo) builds which required standalone engine management. The logging cable alone is $300 and all it does it log, clear codes, and you can tweak little things, but not necessarily the tune or engine management. One reason I'm moving away from Audi. I've put more money into that car than I bought it for already. I love the car but it's too damn expensive to keep up and fix.

 

Sicotic: Check the stickies in the top of the tuning forum. That will get you started. If you have an 06 LGT you may be able to get away with the cheaper Tactrix 1.3 or an ebay VAG-COM cable, but it will be useless on any model year after yours for flashing (logging you still may be able to do). If you want something that's a little faster, allows logging w/o a laptop, and can be used with CAN-BUS ECU's (2008/2007 and newer) get the Tactrix V2 cable from a location of your choosing. It's more expensive but also more versatile.

[Sicotic]

i can buy the vag-com cable and be able to tune my car with it? but anything after my year i cant right?

[DDMan]

From what I have read, yes. That being said you're asking this in my thread where I have said I'm very new to this. I have a 2008 and therefore will have NO experience with the tactrix 1.3 or ebay cable. Read the stickies and make your own determination. I also don't know if there are specific ebay cables that do or don't work.