It seems that the boost pressure shouldn't change at all. Assuming the engine is under load continiously the atmospheric pressure should have no effect (except possibly delaying the build of boost).
Isnt it simply a spring that fully opens at 9psi, slowly opening before that?
How is boost controlled normally
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How is boost controlled normally
Last edited by ciper on Mon Feb 02, 2004 9:02 pm, edited 1 time in total.
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vrg3
- Vikash
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Re: How is boost controlled normally
Not quite.
With the Legacy Turbo, Subaru introduced computer-controlled boost.
The wastegate spring actually opens around 5 or 6 psi. However, the wastegate actuator is not connected directly to the compressor outlet.
The compressor outlet nipple is connected to the boost control solenoid. Another fitting on the solenoid goes to the wastegate actuator. Then there's a third fitting on the solenoid that goes back into the intake, before the compressor.
When the ECU activates the solenoid, boost pressure is bled out this third fitting so it doesn't reach the wastegate actuator. When it deactivates the solenoid, boost pressure goes directly to the wastegate actuator.
The ECU continuously opens and closes the solenoid, varying the pulse width to control how much boost is created. It allows higher boost than the wastegate spring is set to (about 8.7 psi at standard atmospheric pressure), and it allows boost to build more quickly than a direct connection would. And, it increases boost when atmospheric pressure is low. In Ithaca, NY I get around 10 psi, while in DC I get about 9.
With the Legacy Turbo, Subaru introduced computer-controlled boost.
The wastegate spring actually opens around 5 or 6 psi. However, the wastegate actuator is not connected directly to the compressor outlet.
The compressor outlet nipple is connected to the boost control solenoid. Another fitting on the solenoid goes to the wastegate actuator. Then there's a third fitting on the solenoid that goes back into the intake, before the compressor.
When the ECU activates the solenoid, boost pressure is bled out this third fitting so it doesn't reach the wastegate actuator. When it deactivates the solenoid, boost pressure goes directly to the wastegate actuator.
The ECU continuously opens and closes the solenoid, varying the pulse width to control how much boost is created. It allows higher boost than the wastegate spring is set to (about 8.7 psi at standard atmospheric pressure), and it allows boost to build more quickly than a direct connection would. And, it increases boost when atmospheric pressure is low. In Ithaca, NY I get around 10 psi, while in DC I get about 9.
"Just reading vrg3's convoluted, information-packed posts made me feel better all over again." -- subyluvr2212
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Matt Monson
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So how come I keep getting unlimited boost in 4th and 5th gear with my exhaust?
When I first installed the exhaust I didn't reset the ecu and it pegged at 12 psi and stayed there for its first highway run. Eventually, the ecu saw this happening and corrected whatever to keep it at normal boost. Couple of days later my clutch acts up and I send it out to be warrantied.
Fast forward to 3 weeks later when everything is said and done and installed. The ECU reset while the vehicle was waiting for the clutch. I've been driving it like a grandma (sort of...
) and have been shifting before 4k rpm. By the way the power increase was exponential after the ECU was reset, which I knew I needed to do but didn't get around to. Well, almost 500 miles have been put on the clutch and I decide to open her up a bit on the highway... holy crap she rolls out. Small problem, I hit fuel cut. Start watching the boost. In 4th and 5th gear above 4k rpm or so the boost heads straight up to 15 pounds if kept under throttle. I have no form of boost control modification, it is all stock. The pressure isn't creeping, it barrels right past 9 psi.
What could this be? I think I may need to reset the ECU again because of all the putzing around... but why would the ecu need to learn how to control the boost? It doesn't overboost in any other gear, but then again the car doesn't stay in those gears very long before redline hits
. I will try to get it out on the highway again and see if it will control itself. Sorry about the book.
When I first installed the exhaust I didn't reset the ecu and it pegged at 12 psi and stayed there for its first highway run. Eventually, the ecu saw this happening and corrected whatever to keep it at normal boost. Couple of days later my clutch acts up and I send it out to be warrantied.
Fast forward to 3 weeks later when everything is said and done and installed. The ECU reset while the vehicle was waiting for the clutch. I've been driving it like a grandma (sort of...
) and have been shifting before 4k rpm. By the way the power increase was exponential after the ECU was reset, which I knew I needed to do but didn't get around to. Well, almost 500 miles have been put on the clutch and I decide to open her up a bit on the highway... holy crap she rolls out. Small problem, I hit fuel cut. Start watching the boost. In 4th and 5th gear above 4k rpm or so the boost heads straight up to 15 pounds if kept under throttle. I have no form of boost control modification, it is all stock. The pressure isn't creeping, it barrels right past 9 psi.What could this be? I think I may need to reset the ECU again because of all the putzing around... but why would the ecu need to learn how to control the boost? It doesn't overboost in any other gear, but then again the car doesn't stay in those gears very long before redline hits
. I will try to get it out on the highway again and see if it will control itself. Sorry about the book.1993 WMP BC6 5MT EJ22T 9psi 3.9:1 213k 205/55R16
62.6 m/s @ 0.66 bar. Gotta love boost. :)
62.6 m/s @ 0.66 bar. Gotta love boost. :)
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vrg3
- Vikash
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I don't know.Brat4by4 wrote:So how come I keep getting unlimited boost in 4th and 5th gear with my exhaust?
I haven't yet figured out how the ECU's boost control code works. It's not even clear to me whether it's open- or closed-loop. Your experience seems to indicate closed-loop, though.
What kind of exhaust do you have? More specifically, what is the downpipe like? What's its flange like? It's a long shot, but I'm just wondering if it's hampering wastegate operation at all.
The ECU can't be trying to give you that much boost if you hit the fuel cut... I think.
Is there any chance something's up with your pressure sensor? Or some of the vacuum tubing dealing with the pressure sensor, pressure exchange solenoid, or wastegate control solenoid?
"Just reading vrg3's convoluted, information-packed posts made me feel better all over again." -- subyluvr2212
Here are some pics of my exhaust before I put it on. http://www.bbs.legacycentral.org/viewtopic.php?t=1029
It is factory-style downpipe, full 3" mandrel bent, catless, straight-through muffler.
It is quite possible that something with anything boost control related could be wrong, they had the engine out when they replaced the clutch. I will see if boost is controlled in the first three gears or whether I have to shift before there is enough time for boost to build so high. On a side note, I can get full boost at 2k rpm (i know no one would believe me so i tried taking pictures... i'll see if any of them caught it)
I don't think the ECU would be trying to tell the car to boost that high, it just has trouble regulating it (somehow
). I'm thinking I will drop it off at the shop and have them check all vacuum lines and wires that are boost control related. They had a CEL that lit when they first test-drove it... but it went away. I'll have to check that code also.
It is factory-style downpipe, full 3" mandrel bent, catless, straight-through muffler.
It is quite possible that something with anything boost control related could be wrong, they had the engine out when they replaced the clutch. I will see if boost is controlled in the first three gears or whether I have to shift before there is enough time for boost to build so high. On a side note, I can get full boost at 2k rpm (i know no one would believe me so i tried taking pictures... i'll see if any of them caught it)
I don't think the ECU would be trying to tell the car to boost that high, it just has trouble regulating it (somehow
). I'm thinking I will drop it off at the shop and have them check all vacuum lines and wires that are boost control related. They had a CEL that lit when they first test-drove it... but it went away. I'll have to check that code also.1993 WMP BC6 5MT EJ22T 9psi 3.9:1 213k 205/55R16
62.6 m/s @ 0.66 bar. Gotta love boost. :)
62.6 m/s @ 0.66 bar. Gotta love boost. :)
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vrg3
- Vikash
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Hmm... if your downpipe flange is similar to the stock one, I don't think the exhaust itself is the problem...
These vacuum hoses do get hardened and can fail to properly seal when they get old. They can also develop cracks. There's a decent chance that in during removal and reinstallation of the engine some of the hoses were damaged, or that the shop didn't hook the hoses all back up correctly.
You may want to just invest in some new hoses. You could get one of those silicone kits they sell pretty cheaply on eBay, or get the actual hoses from a dealer. I think each of the 6 relevant hoses lists for 10 bucks, and some of the less greedy dealerships should be able to get you better prices.
An advantage with the OEM hoses is that they'll be shaped perfectly, which can be a big help if you ever take them all apart and can't remember how they go back together. You can also be sure that the dynamics of the whole system are as close as possible to OEM spec. You might have to replace them again in 10 years, though...
Unless this shop is really knowledgeable about Legacy Turbos in particular and won't charge you for diagnosis, I'd say just check this stuff yourself. If you want a thorough explanation of what connects to what I could write it out.
These vacuum hoses do get hardened and can fail to properly seal when they get old. They can also develop cracks. There's a decent chance that in during removal and reinstallation of the engine some of the hoses were damaged, or that the shop didn't hook the hoses all back up correctly.
You may want to just invest in some new hoses. You could get one of those silicone kits they sell pretty cheaply on eBay, or get the actual hoses from a dealer. I think each of the 6 relevant hoses lists for 10 bucks, and some of the less greedy dealerships should be able to get you better prices.
An advantage with the OEM hoses is that they'll be shaped perfectly, which can be a big help if you ever take them all apart and can't remember how they go back together. You can also be sure that the dynamics of the whole system are as close as possible to OEM spec. You might have to replace them again in 10 years, though...
Unless this shop is really knowledgeable about Legacy Turbos in particular and won't charge you for diagnosis, I'd say just check this stuff yourself. If you want a thorough explanation of what connects to what I could write it out.
"Just reading vrg3's convoluted, information-packed posts made me feel better all over again." -- subyluvr2212
VRG3 maybe you can help me.
"And, it increases boost when atmospheric pressure is low." vrg3
My legacy up here in Colorado always runs at 8.9 psi, no matter what the elevation. I put a turbo xs boost controller on (between the turbo output and the solenoid). It seems that the most i can get out of it is about 13 psi. I don't think that the fuel cut kicks in though.
Also when it is hooked up this way it will boost more when not under full throttle, go to about 15 psi, and then drop to stock pressure. I have to restart the car to get proper boost.
I've also tried hooking the boost controller form the outlet directly to the wastegate. My boost gauge reads more boost but doesn't pull nearly as hard. Does the solenoid somehow control fuel mixture of ignition timing?
I am planning on making one of those FCD's that you came up with, hopefully it will help.
If anyone has any information let me know. You can email me too. Thanks ,Josh
"And, it increases boost when atmospheric pressure is low." vrg3
My legacy up here in Colorado always runs at 8.9 psi, no matter what the elevation. I put a turbo xs boost controller on (between the turbo output and the solenoid). It seems that the most i can get out of it is about 13 psi. I don't think that the fuel cut kicks in though.
Also when it is hooked up this way it will boost more when not under full throttle, go to about 15 psi, and then drop to stock pressure. I have to restart the car to get proper boost.
I've also tried hooking the boost controller form the outlet directly to the wastegate. My boost gauge reads more boost but doesn't pull nearly as hard. Does the solenoid somehow control fuel mixture of ignition timing?
I am planning on making one of those FCD's that you came up with, hopefully it will help.
If anyone has any information let me know. You can email me too. Thanks ,Josh
Yellow '01 Kaw. ZX-7R (SOLD) :(
Gold '88 Starion ESI-R (Drift Project)
Brgndy '92 Legacy SS, Agency Power Style Headers and Up-pipe (ebay, don't stay together), Underdrive Pully, 5MT conv, mod'd WRX cold air intake and short shifter, 12.5 lb fly
Gold '88 Starion ESI-R (Drift Project)
Brgndy '92 Legacy SS, Agency Power Style Headers and Up-pipe (ebay, don't stay together), Underdrive Pully, 5MT conv, mod'd WRX cold air intake and short shifter, 12.5 lb fly
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vrg3
- Vikash
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Josh - Hmm, weird... It occurs to me that your pressure sensor may be on the fritz, if the ECU isn't compensating for altitude and cutting fuel when overboosting. The latter happened to boostjunkie when his wasn't working.
You ought to be able to get more than 13 psi out of the stock turbo, though (of course, it won't be very efficient). Mine can get up close to 15 or 16 psi. 'Course, the stuff coming out the compressor is more like superheated plasma than air, but... :D
About your weird boost behavior -- can you give more details about how your boost controller is hooked up and where your boost gauge is tapped?
When connecting the wastegate actuator directly to the compressor outlet, you should get the minimum amount of boost -- around 6 psi. The boost control solenoid just bleeds pressure off from the wastegate actuator to increase boost levels; it does nothing else.
What do you expect an FCD to help with? You said you don't get a fuel cut.
You ought to be able to get more than 13 psi out of the stock turbo, though (of course, it won't be very efficient). Mine can get up close to 15 or 16 psi. 'Course, the stuff coming out the compressor is more like superheated plasma than air, but... :D
About your weird boost behavior -- can you give more details about how your boost controller is hooked up and where your boost gauge is tapped?
When connecting the wastegate actuator directly to the compressor outlet, you should get the minimum amount of boost -- around 6 psi. The boost control solenoid just bleeds pressure off from the wastegate actuator to increase boost levels; it does nothing else.
What do you expect an FCD to help with? You said you don't get a fuel cut.
"Just reading vrg3's convoluted, information-packed posts made me feel better all over again." -- subyluvr2212
my MBC is currently in between my compressor outlet and the control solenoid. If I turn it up anymore it will usually go into some kind of protection mode even at full throttle and drop to stock boost when going over about 13 psi.
I never feel a fuel cut above 13 psi when the boost controller is hooked up through the solenoid. I don't think that it is above the 13 psi fuel cut long enough, because the boost drops immediately.
When I have the MBC between the compressor outlet and the wastegate i can get the boost to go to 15 psi or higher and I eventually (after about 3 sec.) hit the brick wall of fuel cut. But the boost just doesn't seem to be as, well, good.
My boost gauge is tee'd in on the line between the manifold and the BOV.
Do you think that bypassing the control solenoid would be a better idea, since it has nothing to do with fuel or spark. Is it neccessary?
A new solenoid would probably help too. Thanks for your help.
I never feel a fuel cut above 13 psi when the boost controller is hooked up through the solenoid. I don't think that it is above the 13 psi fuel cut long enough, because the boost drops immediately.
When I have the MBC between the compressor outlet and the wastegate i can get the boost to go to 15 psi or higher and I eventually (after about 3 sec.) hit the brick wall of fuel cut. But the boost just doesn't seem to be as, well, good.
My boost gauge is tee'd in on the line between the manifold and the BOV.
Do you think that bypassing the control solenoid would be a better idea, since it has nothing to do with fuel or spark. Is it neccessary?
A new solenoid would probably help too. Thanks for your help.
Yellow '01 Kaw. ZX-7R (SOLD) :(
Gold '88 Starion ESI-R (Drift Project)
Brgndy '92 Legacy SS, Agency Power Style Headers and Up-pipe (ebay, don't stay together), Underdrive Pully, 5MT conv, mod'd WRX cold air intake and short shifter, 12.5 lb fly
Gold '88 Starion ESI-R (Drift Project)
Brgndy '92 Legacy SS, Agency Power Style Headers and Up-pipe (ebay, don't stay together), Underdrive Pully, 5MT conv, mod'd WRX cold air intake and short shifter, 12.5 lb fly
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vrg3
- Vikash
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Oh, okay... that's weird. You're hooking your manual boost controller inline with the factory electronic boost controller. You definitely should bypass the stock boost control when installing an MBC. Just put your controller between the compressor outlet nipple and the wastegate actuator nipple.
I don't think you're seeing a "protection mode" at high boost; it's just that the stock turbo isn't very efficient at high boost levels. If you're talking about 13 psi manifold pressure, then you're probably pushing the turbocharger up to 15 psi or even higher, depending on how much pressure drop there is in your intercooler and plumbing. Also, it may take several runs of high boost before the ECU properly learns the appropriate ignition timing; by default it probably runs fairly conservatively when it's so far out of the standard factory ranges.
But, yeah, fuel cut only happens if you're overboosting for more than few seconds; it doesn't prevent boost spikes.
I don't think you're seeing a "protection mode" at high boost; it's just that the stock turbo isn't very efficient at high boost levels. If you're talking about 13 psi manifold pressure, then you're probably pushing the turbocharger up to 15 psi or even higher, depending on how much pressure drop there is in your intercooler and plumbing. Also, it may take several runs of high boost before the ECU properly learns the appropriate ignition timing; by default it probably runs fairly conservatively when it's so far out of the standard factory ranges.
But, yeah, fuel cut only happens if you're overboosting for more than few seconds; it doesn't prevent boost spikes.
"Just reading vrg3's convoluted, information-packed posts made me feel better all over again." -- subyluvr2212
Josh -
One thing to take into consideration is that compressor effeciency is measured in terms of a pressure ratio (PR) instead of an absolute (PSI) output.
So...given that we're at a higher elevation with lower atmospheric pressure (~85% of sea level), the turbo is going to be out of its desirable efficency range sooner (lower boost) than it would at sea level.
This issue is compounded with the fact that we have a relatively small turbo and no intercooler. Sucks, huh?
I'm not too surprised that you don't feel much more punch with the boost turned up. I have an EBC (Blitz SSBC) in my car & noticed similar behavior. At higher boost levels (above 12), the car seemed to fall flat on its face. I wouldn't be surprised if the ECU was pulling timing. Sigh....time for the Link.
Edit - Check out this thread for a little more detail re: stock turbo effeciency.
http://bbs.legacycentral.org/viewtopic.php?t=14816
One thing to take into consideration is that compressor effeciency is measured in terms of a pressure ratio (PR) instead of an absolute (PSI) output.
So...given that we're at a higher elevation with lower atmospheric pressure (~85% of sea level), the turbo is going to be out of its desirable efficency range sooner (lower boost) than it would at sea level.
This issue is compounded with the fact that we have a relatively small turbo and no intercooler. Sucks, huh?
I'm not too surprised that you don't feel much more punch with the boost turned up. I have an EBC (Blitz SSBC) in my car & noticed similar behavior. At higher boost levels (above 12), the car seemed to fall flat on its face. I wouldn't be surprised if the ECU was pulling timing. Sigh....time for the Link.
Edit - Check out this thread for a little more detail re: stock turbo effeciency.
http://bbs.legacycentral.org/viewtopic.php?t=14816
2004 STi
1993 Touring Wagon
1993 Touring Wagon
Actually, I do have an intercooler. A WRX one. I heard from some girl, who owned a white wrx sedan, that a lot of people had been trying to fab. one on the turbo legacy's. I was the only one she knew of that has done it.
Has anyone else been able to get one in thier legacy's? I can try to help if anyone need. Although I don't think it's too efficient with the stock hood scoop. I'm looking into a wrx scoop too.
VRG, thanks for the valuable information. Your one of the most knowledgable people i've talked to. It's good to have you on our side, instead of with all those DSM guys.
DSM's Suck.
Has anyone else been able to get one in thier legacy's? I can try to help if anyone need. Although I don't think it's too efficient with the stock hood scoop. I'm looking into a wrx scoop too.
VRG, thanks for the valuable information. Your one of the most knowledgable people i've talked to. It's good to have you on our side, instead of with all those DSM guys.
DSM's Suck.
Yellow '01 Kaw. ZX-7R (SOLD) :(
Gold '88 Starion ESI-R (Drift Project)
Brgndy '92 Legacy SS, Agency Power Style Headers and Up-pipe (ebay, don't stay together), Underdrive Pully, 5MT conv, mod'd WRX cold air intake and short shifter, 12.5 lb fly
Gold '88 Starion ESI-R (Drift Project)
Brgndy '92 Legacy SS, Agency Power Style Headers and Up-pipe (ebay, don't stay together), Underdrive Pully, 5MT conv, mod'd WRX cold air intake and short shifter, 12.5 lb fly
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vrg3
- Vikash
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Read through the Intercooling forum; plenty of us are intercooled. I had a 94 WRX intercooler on mine but pulled it off when I had some engine trouble and haven't reinstalled it. You're right that the stock hood scoop doesn't flow all that well.
Subarus are the only cars I'll probably ever bother to understand in detail. The effort put into engineering them to be serviceable is unmatched.
Subarus are the only cars I'll probably ever bother to understand in detail. The effort put into engineering them to be serviceable is unmatched.
"Just reading vrg3's convoluted, information-packed posts made me feel better all over again." -- subyluvr2212
I have a 2002 wrx intercooler. It was a pain getting it in. I know those older wrx intercoolers are pretty easy to put in. Sorry, I forgot about those.
Dizzy,
Right now i am living in Laramie, Wyoming. Going to Wyotech. My home is in Aurora, Colorado. If you wanted to take a look at it I would be happy to show you. And you can give me a ride in your STi.
Have you done anything to it yet? I have a theory that you could get like 50hp just from an open element and a boost controller. When does the fuel cut kick in?
Actually we could meet somewhere on a Sunday night. A bunch of people always get together by the Hamburger Stand (I think its in littleton). There's a lot of guys with subarus and even a vishnu stage 2 wrx!
There's also a guy with a supposed 404whp evo 8.
Get back to me.
Dizzy,
Right now i am living in Laramie, Wyoming. Going to Wyotech. My home is in Aurora, Colorado. If you wanted to take a look at it I would be happy to show you. And you can give me a ride in your STi.
Have you done anything to it yet? I have a theory that you could get like 50hp just from an open element and a boost controller. When does the fuel cut kick in?
Actually we could meet somewhere on a Sunday night. A bunch of people always get together by the Hamburger Stand (I think its in littleton). There's a lot of guys with subarus and even a vishnu stage 2 wrx!
There's also a guy with a supposed 404whp evo 8.
Get back to me.
Yellow '01 Kaw. ZX-7R (SOLD) :(
Gold '88 Starion ESI-R (Drift Project)
Brgndy '92 Legacy SS, Agency Power Style Headers and Up-pipe (ebay, don't stay together), Underdrive Pully, 5MT conv, mod'd WRX cold air intake and short shifter, 12.5 lb fly
Gold '88 Starion ESI-R (Drift Project)
Brgndy '92 Legacy SS, Agency Power Style Headers and Up-pipe (ebay, don't stay together), Underdrive Pully, 5MT conv, mod'd WRX cold air intake and short shifter, 12.5 lb fly
Josh -Have you done anything to it yet? I have a theory that you could get like 50hp just from an open element and a boost controller. When does the fuel cut kick in?
The STi is bone stock. It's going to stay that way for a while. I'll spend money on more driving lessons before I throw money/go-fast parts at it. It's fast enough stock. My guess is fuel cut will happen around 17psi at this altitude. That is around where I would hit it with my WRX.
My wagon is my 'tuner' car. It's a bit pokey & has some room for improvement (handling & speed).
2004 STi
1993 Touring Wagon
1993 Touring Wagon