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Old 05-06-2005, 03:15 PM   #1
spyder_gsr
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Default ECU as boost controller?

Does the ECU in these cars (04 WRX) control the boost to the point that it is acting like a boost controller? I here talk about getting this ECU (or that one) will adjust your boost levels to 14.5 psi. Is this correct or is the ECU only ALLOWING the boost to reach those levels if you have a boost controller set? I'm new to these cars and I'm coming from the DSM world.

TJ
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Old 05-07-2005, 03:48 PM   #2
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The ECU in a stock car controls boost. A reflash, or new computer will allow you to set boost within limited parameters, but those limits are fairly wide with some, and very narrow with others. If you are starting out, get some engine management, and skip a boost controller.
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Old 05-07-2005, 04:20 PM   #3
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The stock boost in a wrx is around 13.5-14.5psi at full throttle in low-mid rpm ranges. The boost will naturally fall off a bit at higher rpms cause it can't really keep up with the flow of the engine at those boost levels(since it's tiny).

peace
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Old 05-07-2005, 09:32 PM   #4
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Quote:
Originally Posted by spyder_gsr
Does the ECU in these cars (04 WRX) control the boost to the point that it is acting like a boost controller? I here talk about getting this ECU (or that one) will adjust your boost levels to 14.5 psi. Is this correct or is the ECU only ALLOWING the boost to reach those levels if you have a boost controller set? I'm new to these cars and I'm coming from the DSM world.

TJ
The ECU controls boost via a solenoid which takes a sample of the boost and sends a voltage to the ECU corresponding to how much boost the turbo is making. It then sends a signal to the WG actuator to open or close the wastegate depending on what the car is boosting.

A boost controller "fakes" out the ECU by bleeding off the wastegate solenoid boost sample to make the ECU think its boosting less, when in reality its boosting more. (I think, I may be backwards/confused).

An aftermarket piggyback (UTEC, Xede) will alter the signals going to the STOCK ECU and control boost that way.

A reflash will reprogram the stock ECU's boost tables to make more boost, as opposed to altering the incoming signals.

Aaron
(feel free to correct as needed )
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Old 05-07-2005, 10:24 PM   #5
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The solenoid doesn't take a sample of anything. The ecu uses the map(manifold absolute pressure) sensor to determine the boost the turbo is making. The ecu uses the solenoid to bleed or hold pressure in the tubing going to the wastegate actuator to control the wastegate and limit the boost.

peace
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Old 05-08-2005, 03:06 PM   #6
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I knew something sounded off. Ha.
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Old 05-16-2005, 10:14 AM   #7
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Quote:
Originally Posted by hippy
The solenoid doesn't take a sample of anything. The ecu uses the map(manifold absolute pressure) sensor to determine the boost the turbo is making. The ecu uses the solenoid to bleed or hold pressure in the tubing going to the wastegate actuator to control the wastegate and limit the boost.

peace
I thought these cars were a MAF setup and not MAP? So what is the limit of boost that the ECU can handle? Can it be set to boost say 20psi? How does it do this? Is there a "boost" parameter in the ecu? Or does a piggyback or reflash still "fool" the ecu by feeding adjusted readings to get boost up?

(I love it when you ask a question and someone explains the innerworkings of a boost controller. Priceless! yes I know how a boost controller works and I know how the boost sol. works but how does the ECU control it for the purpose of raising boost?)

For example, on the DSM side the boost sol. would limit boost and have the ability to pull boost if something goes wrong. (knock, etc...) But the ECU does not have the programming to "up" the boost. It sounds like the WRX does.

Although judging from a lot of posts here it sounds like some people are having problems getting there "modded" ECU to bring the boost up to were it is claimed it should be.

TJ
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Old 05-16-2005, 11:45 AM   #8
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Quote:
Originally Posted by spyder_gsr
I thought these cars were a MAF setup and not MAP? So what is the limit of boost that the ECU can handle? Can it be set to boost say 20psi? How does it do this? Is there a "boost" parameter in the ecu? Or does a piggyback or reflash still "fool" the ecu by feeding adjusted readings to get boost up?

(I love it when you ask a question and someone explains the innerworkings of a boost controller. Priceless! yes I know how a boost controller works and I know how the boost sol. works but how does the ECU control it for the purpose of raising boost?)

For example, on the DSM side the boost sol. would limit boost and have the ability to pull boost if something goes wrong. (knock, etc...) But the ECU does not have the programming to "up" the boost. It sounds like the WRX does.

Although judging from a lot of posts here it sounds like some people are having problems getting there "modded" ECU to bring the boost up to were it is claimed it should be.

TJ
Yes, the ECU has a "boost" cell (really cells based on different conditions) that allows smart people to upload whatever boost value they want the turbo to try to make. There have been issues w/ the Cobb units being able to hit the target boost, but this is probably more of an issue b/c its a single solution being offered to many different cars, and its not tunable. Other reflashes (EcuTek) & piggybacks (UTEC, etc...) usually don't have a problem adjusting the boost to hit what you want.
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Old 05-16-2005, 12:52 PM   #9
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Quote:
Originally Posted by spyder_gsr
I thought these cars were a MAF setup and not MAP? So what is the limit of boost that the ECU can handle? Can it be set to boost say 20psi? How does it do this? Is there a "boost" parameter in the ecu? Or does a piggyback or reflash still "fool" the ecu by feeding adjusted readings to get boost up?

(I love it when you ask a question and someone explains the innerworkings of a boost controller. Priceless! yes I know how a boost controller works and I know how the boost sol. works but how does the ECU control it for the purpose of raising boost?)

For example, on the DSM side the boost sol. would limit boost and have the ability to pull boost if something goes wrong. (knock, etc...) But the ECU does not have the programming to "up" the boost. It sounds like the WRX does.

Although judging from a lot of posts here it sounds like some people are having problems getting there "modded" ECU to bring the boost up to were it is claimed it should be.

TJ
The car is MAF based for fueling, and MAP based for boost control.

When you get a reflash it reprograms the factory ECU to new parameters. No fooling like a piggyback. Yes there is a boost map in the factory ECU. Both target boost, and predicted wastegate duty cycle to achieve target. The duty cycle map is a learning map so that when the weather changes your boost stays consistent.

The ECU won't pull boost for knock. It will pull timing though, as that is more the culprit than boost levels.

You can get a reflash to run any boost level, timing, afrs you want essentially. The stock turbo is way too small to run more than ~12-13 psi at redline though.
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Old 05-16-2005, 01:35 PM   #10
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There are a few limiting factors when it comes to boost with stock parts. First would be that the bcs can only vent a given amount of air. Once the bcs vents as much as it can and the wastegate opens from there being to much pressure in the tubing going to the wastegate actuator, you're pretty much at the mechanical limits of the system. Being this close to the edge might also create slow spooling characteristics. Many companies try to overcome this in different ways. Turboxs puts a bleed valve between the bcs and turbo to vent off a given amount of extra air. Some other companies put brass restrictors with smaller holes in them then the stock one in the tubing coming off the turbo to limit the air going to the bcs so it doesn't have to work as hard.

Another limitation would be the map sensor. Since it doesn't register higher then something like 23 or so psi, controlling boost at 30psi with the map sensor would be pretty hard. If you're planning on upping the boost without a reflash of some sort(like by just puting in a mbc and raising the boost), you're also gonna be limited by the ecu's overboost fuel cut. I think it's at something like 17.5psi on a stock wrx, maybe 18.5 I forget. Piggybacks get around this by making the ecu think the boost is always lower then the fuel cut amount, and I'm not really sure how reflashes fix this(they must be able to change the fuel cut amount).

peace
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Old 05-16-2005, 02:41 PM   #11
mbiker97
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Quote:
Originally Posted by hippy
and I'm not really sure how reflashes fix this(they must be able to change the fuel cut amount).
You can change the value that triggers boost cut with ECUtek (I'm not sure about Cobb).
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