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Discussion Starter #1 (Edited)
Well, it seems like I've answered the same question thirty times in the past week, so I figured I'd make a sticky post and leave it there for everyone to see....

Q: What does a boost controller do?
A: A boost controller allows the user to specify a certain boost level for their turbo.

Q: Are they okay to put on a WRX/STi?
A: No.

Q: Why not?
A: All engines run best at a certain Air/Fuel ratio. Different cars run better at different AFR's, but forced induction engines (turbo and supercharged) usually require a richer AFR than naturally aspirated engines.

Your computer is programmed from the factory to control the boost that the turbocharger makes based on RPM and load (how hard the engine is working). It takes those two factors into account and determines how much fuel to put into the engine to reach a desired AFR. It also adjusts your timing to get the best performance while still avoiding knock (detonation).

When you raise your boost, you throw all those readings out of whack. Your ECU reads throttle position and load, and determines how much boost and fuel should be going into your engine to reach the desired AFR. If you use a boost controller (either manual or electronic) you are overriding the ECU's control of boost. The ECU thinks the boost has not changed, but in reality it has. So, it puts the same amount of fuel into the engine that it would put in if it were still in control of boost. However, you are putting more boost (more air) into the engine, which creates a leaner AFR. Lean AFR's are the #1 cause of detonation, and detonation is the number one cause of engine failure.

Q. What about a downpipe? Doesn't that raise boost?
A. Yes, it does. But it only raises peak boost slightly, and only under full load. A boost controller allows full boost at any load and RPM. Your ECU runs richer at full load and high rpm to take extra precautions against detonation.

Q. What is Partial Throttle Full Boost?
A. Partial throttle full boost is the biggest danger associated with boost controllers. We have already discussed how the ECU regulates boost based on rpm and load. A boost controller does not factor load or rpm into the equation. It works on pressure only. It will allow your turbo to reach full boost at 3000 rpm or 7000 rpm. And, it will allow it at 10% load or 100% load, or anywhere in between. At full throttle it may be okay, because the computer is still adding the fuel it thinks the car needs. But, at partial throttle it is adding very little fuel, because it thinks the car is only making a small amount of boost, which leads to extremely lean conditions. I have seen AFR's in the 19:1 range pretty commonly with a boost controller at partial throttle.

So, just say no to boost controllers.

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forgive me for asking the newbie question but doesn't swapping in a new downpipe raise the boost from 13.5 to say 14.5? Isn't that raising the boost without changing the fuel system?
 

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n00b as well

I'm n00b as well... And I have a question too.

I've heard that the ECU is a learning ECU... I guess in the short run raising boost so suddenly might mess up your engine. But, assuming your engine hasn't messed up, then after a while does our ECU's adjust to the extra oxygen it's getting?
 

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Discussion Starter #5
No. The "learning" is based on how you drive, and it only works if the ECU is still in control of everything. It may adjust the fuel and timing slightly over the course of a few months, but not nearly to the extent everyone says it does. And, not nearly enough to compensate for the extra boost. Especially at lower rpm and load points.

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just a clarification...
I know I read it in one of the post here (I just can't find it anymore)
that it would be okay to put a boost controller to a stock car
as long as it's not set more than peak boost. (14 psi)
It would make the car spool up sooner and be more driveable...
Is this wrong???
 

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The boost controller that coems with the UTEC is an auxilary boost control. It is for the fine, small adjustments you need to make such as based on temperature and weather. You leave that on or the UTEC will not function right.
 

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wrx555 said:
just a clarification...
I know I read it in one of the post here (I just can't find it anymore)
that it would be okay to put a boost controller to a stock car
as long as it's not set more than peak boost. (14 psi)
It would make the car spool up sooner and be more driveable...
Is this wrong???
Cosmo said:
I wouldn't do it. You can do it, and I have done (and suggested) it before, but I am now saying that I wouldn't do it. This is after datalogging many cars with a MBC and watching their AFR curves change dramatically.
Cosmo,
Thank you for sharing this information. I was intending to swap in a ball & spring MBC (and boost gauge) off of my Talon to regulate to a conservative ~13psi, with a goal of increasing 1st and 2nd gear boost.

I would greatly appreciate it if you could provide any hard numbers of what you have observed, correlating the a/f ratio with the boost & throttle position. Doesn't have to be precise, just ball park numbers that you recall. If it is somewhere south of 12.0 a/f under all TPS values for 13psi, I may still be satisfied since I will be installing my water injection system as well for some additional safety. This is assuming that WRX's do not run super aggressive timing, which I will need to research first (just started researching yesterday).

I know that replacing the first cat is highly recommended for increasing boost / power, but I would much prefer to keep my exhaust system stock at the expense of less power. I'm at a stage in life of caring more about the exhaust I'm shooting at the person behind me in traffic :)

Thanks much!
-Adrian
 

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I bought a Perrin Boost Controller prior to reading this post (one of the tech's at my Subaru dealership has one on his Legacy and had one on his past WRX and STi's) and was wondering what I should do.

The guy said he would install it for me and that as long as it's not set very high, it should increase the reponse time of my turbo (i have an auto so there's quite a bit of lag.) I'm not going to have it set aggressively and I understand that if the ECU does not expect to have the turbo running at lower rpm, there could be an issue but I'm wondering what the real long term effects would be.

I'm speaking not as a hardcore racer, but more of a casual one that wants to get rid of my lag as cheaply as possible yet still have this car last me a good 10-15 years.

I understand it's not the best mod in the world, but if installed by a guy at my dealership would it really be a large, warrantee-killing risk? The reason I say it that way is because it's already in the mail - if it's really a big problem, I can try to cancel it/send it back but just making sure.
 

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if you want the car to last 10-15 years, the least you can do for it is buy an ECU upgrade instead of a boost controller. The AP and UTEC will both help with boost and won't cause near as much damage.

but any time you raise power over stock, you ARE reducing the life if the car. Just not by very much sometimes.
 

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ahains said:
Cosmo,
Thank you for sharing this information. I was intending to swap in a ball & spring MBC (and boost gauge) off of my Talon to regulate to a conservative ~13psi, with a goal of increasing 1st and 2nd gear boost.

I would greatly appreciate it if you could provide any hard numbers of what you have observed, correlating the a/f ratio with the boost & throttle position. Doesn't have to be precise, just ball park numbers that you recall. If it is somewhere south of 12.0 a/f under all TPS values for 13psi, I may still be satisfied since I will be installing my water injection system as well for some additional safety. This is assuming that WRX's do not run super aggressive timing, which I will need to research first (just started researching yesterday).

I know that replacing the first cat is highly recommended for increasing boost / power, but I would much prefer to keep my exhaust system stock at the expense of less power. I'm at a stage in life of caring more about the exhaust I'm shooting at the person behind me in traffic :)

Thanks much!
-Adrian
Now that I am a bit older and wiser on WRX's, I thought I'd reply back to myself.
The fact is that on 04 and 05 WRX's, the stock programming will target 14.7/1 AFR even at full boost. This is horrible horrible horrible. Not only would I NEVER but a boost controller on a stock 04 or 05, I wouldn't put up with leaving the factory programming in place.
If you know anyone in your area with an OpenPort cable from tactrix.com in your area, they can use free software to flash your stock ECU with some changes to the open loop/close loop delay and protect you from this horrible stock programming.

Once you do this, it is not nearly as risk to up the boost slightly with a boost controller. Although it is better just to use the same cable to edit your boost targets in the stock ECU to raise the pressure. Since there is not yet a published tool to do this it means busting out your hex editor, but it is not hard if you are a geek :)

-Adrian
 

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doesn't the ecu sense load via the output voltage from the hot wire mass air flow meter?
the factory ecu measures the air entering the engine, not the boost pressure, the map sensor is only used for boost cut purposes, so the load axis is actually cfm not psi. the problems you mentioned occur because the airflow exceeds the maximum allowable cfm which the ecu is tuned for. (afm voltage goes out of range) and as a result the ecu can no longer calculate the engines fuel requirements, as a result it either makes it excessively rich (safety feature when excessive airflow is detected the ecu dumps massive amounts of fuel in to avoid detonation) or excessively lean (fuel system cannot flow the required fuel)depending on how far the boost is raised. The heat in the stock intercooler due to raised boost pressure can also lead to detonation.
90% of ebc related engine failures is a result of the owner setting a boost target to high (owners often creep the pressure up a little bit at a time over a few weeks or months and then they get a batch of bad fuel or a hot day and things go bang) or using inferior fuel with the raised boost pressure but not owning up to their own stupidity and using the good old excuse of "it just blew up, i didnt do anything out of the ordinary."
i have set up many ebcs on wrxs which run max pressure of 16.8psi from 3200rpm, and tell the owner they have to use BP Ultimate (98 Octane pump gas) and things run fine. The factory boost cut at 17psi is there for a good reason, the ecu only meters airflow a small amount above this.
if it was possible to setup a someones ebc and pull all the adjusting knobs off so they couldnt fiddle with things many more engines would survive.
 

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mosc said:
forgive me for asking the newbie question but doesn't swapping in a new downpipe raise the boost from 13.5 to say 14.5? Isn't that raising the boost without changing the fuel system?
Does the 1.0psi increase hold true for a Helix catted DP? The cat is a high flow cat and I have noticed more torque since adding it. Note: I had an upipe installed before my dp but didn't notice any difference with it. I have another question but will leave that for a different thread.
 

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stileguy said:
doesn't the ecu sense load via the output voltage from the hot wire mass air flow meter?
the factory ecu measures the air entering the engine, not the boost pressure, the map sensor is only used for boost cut purposes, so the load axis is actually cfm not psi.
Anyone know for a fact which is correct?

I'm from the DSM (eclipse turbo) world where this is how things work. I'm trying to understand what makes the STi ECU different. Everyone talks about needing new maps for every little change. On my eclipse as long as you had a big enough fuel pump and injectors you could throw on any size turbo, downpipe, exhaust, whatever and not have to make any tuning changes (mostly).
 
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