Boost Controllers and You... - Subaru WRX Forum
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post #1 of 37 Old 05-11-2005, 08:50 AM Thread Starter
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Boost Controllers and You...

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.

Last edited by Cosmo; 05-11-2005 at 10:43 AM.
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post #2 of 37 Old 05-11-2005, 10:17 AM
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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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post #3 of 37 Old 05-11-2005, 10:33 AM Thread Starter
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Yes, it does. There is enough extra fuel in there to compensate for that. However, that only occurs as peak boost. Which reminds me of something else I need to add....
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post #4 of 37 Old 05-11-2005, 10:33 AM
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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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post #5 of 37 Old 05-11-2005, 10:44 AM Thread Starter
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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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post #6 of 37 Old 05-12-2005, 10:38 AM
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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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post #7 of 37 Old 05-12-2005, 10:41 AM Thread Starter
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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.
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post #8 of 37 Old 05-12-2005, 04:57 PM
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So take the MBC that came with my UTEC off, and then how do I maintain the boost though?
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post #9 of 37 Old 05-12-2005, 09:57 PM
 
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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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post #10 of 37 Old 05-12-2005, 10:30 PM Thread Starter
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The ABC that comes with the UTEC is not a boost controller. It bleeds off pressure to allow the stock boost control solenoid to control boost with the added pressure of higher boost levels.
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post #11 of 37 Old 05-13-2005, 09:13 PM
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Thumbs up Once again

Thankyou Cosmo and UCLA
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post #12 of 37 Old 05-20-2005, 11:00 AM
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Quote:
Originally Posted by wrx555
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???
Quote:
Originally Posted by Cosmo
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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post #13 of 37 Old 07-12-2005, 08:38 PM
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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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post #14 of 37 Old 07-13-2005, 02:16 PM
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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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post #15 of 37 Old 08-27-2005, 12:12 PM
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If you put a MBC on and turn you boost down will you conserve gas????
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