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Old 11-08-2009, 08:11 AM   #201
ride5000
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as long as your map has sensical values for timing/fuel, and you're SURE you're not running in CL, then PTFB isn't "harmful" to the engine. in fact, long, long, long time ago, someone (vaus) made up a simple little discreet circuit that used to send a 100% tps signal to the ecu when boost went above a settable trigger point. basically it would force the 16bit ecu into open loop regardless of "actual" throttle angle. it worked fine to prevent the negative effects of PTFB.

nowadays we just reflash the ecu! good times..

there is one negative aspect of PTFB--the turbo works "extra hard" against the restriction of the partially closed throttle. in turn, that increases the exhaust gas backpressure, hurting VE. as a result, it is far more elegant to keep boost lower until the throttle angle becomes higher, but it's not really detrimental to longevity.
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Old 11-08-2009, 08:22 AM   #202
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Thanks ride for the detailed explanation. Much appreciated. So an mbc is compatible with Accessport? Do u mean sensible ratios?
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Old 11-25-2009, 10:38 PM   #203
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Can someone with an in depth knowledge of the GM BCS tell me if this is correct... If you have to MBC in line with the GM BCS, is compressed air being lost through the BCS if its duty cycle is at 100% and the spring preload of the MBC is overcome, or is the diagram that I have drawn up of how the GM BCS wrong? If the solenoid is just opening and closing the connection inside of the valve in that spot, then when the MBC opens, some of the air is going to be lost through the lines that lead back to the turbo inlet... Any imput???
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Old 11-25-2009, 11:21 PM   #204
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You're basically right. But when the MBC is letting pressure through to the actuator, you're above the boost target, so losing boost is not a concern.

The more interesting thing, IMO, is that when the MBC is closed (i.e. you're below target boost) the solenoid is routing air from the compressor to the turbo inlet.

Last edited by NSFW; 11-26-2009 at 01:38 PM. Reason: further thinking
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Old 11-26-2009, 12:19 AM   #205
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Wouldn't losing that air reduce compressor efficiency though? Even though it remains in the system and is not losing metered air, it's still wasted air/needs to be re-compressed. Idk maybe it's so minor it isn't really important?
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Old 11-26-2009, 01:08 AM   #206
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Forget what I wrote here.

Last edited by NSFW; 11-26-2009 at 01:38 PM. Reason: I may have been smoking crack at the time.
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Old 11-26-2009, 03:39 AM   #207
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Are you guys setting your target boost levels in your maps the same as what you are setting your MCB's to? If so I could see that working out, but it seems like a waste to be bleeding off that compressed air to be re compressed again and again. If you had the target boost level set EXACTLY the same as the MBC then the solenoid would block pressure where the red arrow is in the drawing of the BCS and you wouldn't be loosing that pressure to the turbo inlet pipe. I know that it is probably close to impossible for that be to achieved, but it seems like you would be making your turbo less efficient if its loosing all of that airflow.
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Old 11-26-2009, 09:18 AM   #208
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Quote:
Originally Posted by NSFW View Post
You're basically right. But when the MBC is letting pressure through to the actuator, you're above the boost target, so losing boost is not a concern.
Losing the boost is of concern, it is less air going into the engine (though it may be a small amount). It is also metered air.

You can put a restrictor in the line that bleeds to atmosphere to minimize this.
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Old 11-26-2009, 09:34 AM   #209
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Quote:
Originally Posted by 02RexWI View Post

Can someone with an in depth knowledge of the GM BCS tell me if this is correct... If you have to MBC in line with the GM BCS, is compressed air being lost through the BCS if its duty cycle is at 100% and the spring preload of the MBC is overcome, or is the diagram that I have drawn up of how the GM BCS wrong? If the solenoid is just opening and closing the connection inside of the valve in that spot, then when the MBC opens, some of the air is going to be lost through the lines that lead back to the turbo inlet... Any imput???
my input is stick a cork in it so that it does not flow any air.

it doesn't need to bleed anything. the solenoid is either open (and boost is wastegate) or closed (and the mbc is in charge).

as far as how much air this is, it is minuscule. you wouldn't even see the effect in your fuel trims. keep in mind when the BCS is really venting the engine is consuming ~250-300g of air a SECOND. the density of air is ~1.19g/L. in other words, there is a HUGE volume of charge air getting sucked into the cylinders and the tiny amount passing out a length of 1/8th inch ID hose after first finding its way through a solenoid is a drop in the bucket.
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Old 11-26-2009, 10:03 AM   #210
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my input is stick a cork in it so that it does not flow any air.

it doesn't need to bleed anything. the solenoid is either open (and boost is wastegate) or closed (and the mbc is in charge).

as far as how much air this is, it is minuscule. you wouldn't even see the effect in your fuel trims. keep in mind when the BCS is really venting the engine is consuming ~250-300g of air a SECOND. the density of air is ~1.19g/L. in other words, there is a HUGE volume of charge air getting sucked into the cylinders and the tiny amount passing out a length of 1/8th inch ID hose after first finding its way through a solenoid is a drop in the bucket.
I agree that you probably wouldn't notice a difference in power if you were to run it back to back on a dyno, but the fact is: there is a slight flaw in the system. Sorry, i'm kind of a perfectionist! As for putting a cork in it, wouldn't that cause a problem with the wastegate sticking open since it wouldn't have anywhere to bleed the pressure off to after you let off the gas, or would the BCS switch off for a period of time when you let off the gas: thus bleeding the pressure back through the compressor housing? I did think about the restrictor pill idea, but thats kind of like putting a bandage on it...
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Old 11-26-2009, 11:05 AM   #211
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Quote:
Originally Posted by ride5000 View Post
my input is stick a cork in it so that it does not flow any air.

it doesn't need to bleed anything. the solenoid is either open (and boost is wastegate) or closed (and the mbc is in charge).

as far as how much air this is, it is minuscule. you wouldn't even see the effect in your fuel trims. keep in mind when the BCS is really venting the engine is consuming ~250-300g of air a SECOND. the density of air is ~1.19g/L. in other words, there is a HUGE volume of charge air getting sucked into the cylinders and the tiny amount passing out a length of 1/8th inch ID hose after first finding its way through a solenoid is a drop in the bucket.

+1 on blocking the port, although I hear some blocking solenoids need a bit of air movement to work properly, hence the suggestion to have a restrictor in it.

On my hybrid set-up the solenoid blocks air as soon as I get above 2500 rpm, I am not flowing 250 g/s at that point, maybe 130 or so. So no, it will not affect fuel trims, as it only causes a leak in OL, but it will still be an air leak. How much of one? Depends on your solenoid. I hear the GS one has fair sized ports, so if you used 1/4 line everywhere it could add up to a bit of air, especially on spool.


Quote:
Originally Posted by 02RexWI View Post
I agree that you probably wouldn't notice a difference in power if you were to run it back to back on a dyno, but the fact is: there is a slight flaw in the system. Sorry, i'm kind of a perfectionist! As for putting a cork in it, wouldn't that cause a problem with the wastegate sticking open since it wouldn't have anywhere to bleed the pressure off to after you let off the gas, or would the BCS switch off for a period of time when you let off the gas: thus bleeding the pressure back through the compressor housing? I did think about the restrictor pill idea, but thats kind of like putting a bandage on it...
The actuator will not stick open as once your WGDC goes down under 100% any pressure will go back into the comp housing.

1/4 line would allow a few (my guess 5) g/s of air through. IMO 5 is 5 whp, so it matter. A little restrictor would easily get that down to 1 or less, IMO not significant.
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Old 11-26-2009, 11:08 AM   #212
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Quote:
Originally Posted by 02RexWI View Post
I agree that you probably wouldn't notice a difference in power if you were to run it back to back on a dyno, but the fact is: there is a slight flaw in the system.
if we're keeping track, there are an infinite number of flaws in the system the way it comes from FHI.

no reason to start here.

Quote:
Sorry, i'm kind of a perfectionist! As for putting a cork in it, wouldn't that cause a problem with the wastegate sticking open since it wouldn't have anywhere to bleed the pressure off to after you let off the gas, or would the BCS switch off for a period of time when you let off the gas: thus bleeding the pressure back through the compressor housing? I did think about the restrictor pill idea, but thats kind of like putting a bandage on it...
you haven't read the thread, have you?

the answer is, in my experience, and contrary to what i initially assumed, you do not need a bleed to allow the WGA to return to the rest position.

there may be a flaw in your incarnation, but it doesn't exist in mine.
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Old 11-26-2009, 11:15 AM   #213
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1/4 line would allow a few (my guess 5) g/s of air through. IMO 5 is 5 whp, so it matter. A little restrictor would easily get that down to 1 or less, IMO not significant.
you are absolutely smoking crack if you think 5g/s flows though the comp nipple, through your hookup hose, through the solenoid, and through your discharge hose.

5g/s will net you about a 3-4krpm idle. you think you can get the engine to idle that high pulling ALL of its intake air through that plumbing?

surely you have seen the port sizes on the gm solenoid.. or the grainger? how big are they compared to the port on the IACV?

not that it matters, because you don't need the bleed in the first place, but let's not just throw arbitrary numbers around. the idea that blowing off your boost control pressure signal costs you 5hp is ridiculous.
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Old 11-26-2009, 12:45 PM   #214
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Quote:
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you are absolutely smoking crack if you think 5g/s flows though the comp nipple, through your hookup hose, through the solenoid, and through your discharge hose.

5g/s will net you about a 3-4krpm idle. you think you can get the engine to idle that high pulling ALL of its intake air through that plumbing?

surely you have seen the port sizes on the gm solenoid.. or the grainger? how big are they compared to the port on the IACV?

not that it matters, because you don't need the bleed in the first place, but let's not just throw arbitrary numbers around. the idea that blowing off your boost control pressure signal costs you 5hp is ridiculous.
Not crack, must be something else.

Maybe 2 g/s.
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Old 11-26-2009, 12:52 PM   #215
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I take that back, I am not on crack. Maybe 2 to 3 g/s if 1/4 hosing.

A vacuum leak on the IM will cause fuel trims to go out more then 25% (on the cars that have 25 vs 15% allowed in trims), and that line can only be 1/8inch diameter.

If you had 1/4 inch hosing (which I said before) do the math, figure out the X-sectional area of that line, then figure it out for your intake piping (likely 2.5 inch piping going to FMIC)

Don't forget, if you are running 23 psi, then the comp housing of the turbo is likely at 25+.
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Old 11-26-2009, 01:21 PM   #216
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So does everyone agree then it should be safe to cap off the intake return line? And it's better for performance in the sense that it will eliminate the "leak"? I've seen small dips in my AFR that I haven't been able to completely tune out so I'm thinking this is the cause. If it's safe to do that I will cap mine off and re-calibrate the MAF to see if that helps.
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Old 11-26-2009, 01:39 PM   #217
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Losing the boost is of concern, it is less air going into the engine (though it may be a small amount). It is also metered air.

You can put a restrictor in the line that bleeds to atmosphere to minimize this.
It's being recirculated post-MAF though, so metering is a non-issue.
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Old 11-26-2009, 02:21 PM   #218
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It's being recirculated post-MAF though, so metering is a non-issue.
Isn't it still kind of an issue though, even though it's being metered, it's not making it to the cylinder when expected, kind of like how a fmic can cause a rich dip as it pressurizes. Or am I way off? Don't get me wrong, I'm a huge fan of this setup and have been using it for a while, just trying to figure out the best way to do it.

Edit: I definitely don't want to vta, so that is not an option for me.
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Old 11-26-2009, 03:28 PM   #219
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^It sounds like its not going to be a problem to cap off the line that goes to the turbo inlet, because like littlebluegt said, once you let off the gas the solenoid will open and bleed any pressure left in the wastegate actuator back through the compressor housing.

-You're right, I haven't read all the posts, but now that we have this figured out, I think that someone should make a correction to the install instructions of the vacuum lines for this setup, because even though you guys may think that a little pressure being lost isn't a BIG deal, it is still happening the way that people are showing to run the lines, and the bottom line is that they are loosing some efficiency by routing the lines that way and there in no need for it.
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Old 11-26-2009, 05:08 PM   #220
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Isn't it still kind of an issue though, even though it's being metered, it's not making it to the cylinder when expected, kind of like how a fmic can cause a rich dip as it pressurizes. Or am I way off?
Recirculating means that the air going back to the inlet prevents an equal amount of 'new' air from going past the MAF sensor... bottom line is, the amount of air going past the sensor is equal to the amount of air entering the cylinder.

If there were a large chamber in between the turbo and the inlet that needed to be filled (the volume of a FMIC, for example ) before the the recirculated air made it to a point where it could prevent further intake, then that time lag would create a rich dip, but there isn't one in this case.
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Old 11-26-2009, 05:50 PM   #221
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My comment about metered air was if it is not recirced to the intake.

I don't think we are being anal, Subaru didn't bleed the OEM system (with a restrictor pill I might add, not just a 1/8 inch line) to atm, they recirc'd it!
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Old 11-26-2009, 07:18 PM   #222
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You guys are way overthinking this. The minuscule amount of charge air lost is not an issue at all.
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Old 11-26-2009, 09:13 PM   #223
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Cool. I'm going to cap off the intake return port on my grimmspeed bcs and we'll see how it goes.
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Old 11-26-2009, 09:51 PM   #224
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You guys are way overthinking this. The minuscule amount of charge air lost is not an issue at all.
If people didn't overthink situations like this then progress wouldn't be made
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Old 11-27-2009, 07:25 AM   #225
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My comment about metered air was if it is not recirced to the intake.

I don't think we are being anal, Subaru didn't bleed the OEM system (with a restrictor pill I might add, not just a 1/8 inch line) to atm, they recirc'd it!
due to emissions control laws, ANY molecule of air that goes INTO the intake tract MUST eventually exit via the tailpipe.

we don't have such constraints.
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