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Discussion Starter · #1 ·
so I was changin my oil recently and got to looking at the boost relief valve. Is that little hose going to that black valve the only thing venting our boost away from the car. If so how is it able to bleed 3 psi though a vaccuum line? Why would it not be possible to remove the valve totally? I mean it might throw an SES but it would work?
 

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Are you talking about the solenoid that opens the internal bypass valve? That's how it bleeds boost if I'm not mistaken. It's not through the hose, it's referenced off the hose. The bypass is internal, so it just starts opening the bypass a little as we get past 12 psi. Or am I talking about something different?
 

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Discussion Starter · #3 ·
Sp00ner said:
Are you talking about the solenoid that opens the internal bypass valve? That's how it bleeds boost if I'm not mistaken. It's not through the hose, it's referenced off the hose. The bypass is internal, so it just starts opening the bypass a little as we get past 12 psi. Or am I talking about something different?
I'm going on 3 hours of sleep here so I'm trying to be coherent. Now let me remember what I saw under my hood. The vaccuum diagram had a hose coming from the intake manifolt to a solenoid and then to what it called a bypass valve (was external black round thing) and that went into the sc head unit. If it is something internal where is it internally? Is it in the sc? Where does it bleed it to?
 

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Yes, the bypass is internal to the supercharger. There's a great moving demo pic of it around here somewhere. There's a butterfly type of thing that lets the air skip the blower as it opens up. So instead of letting boost out of the car, it simply begins to open the valve more and more, so the air goes around the compressor. That's what happens when crusing on the highway. The valve opens and the air routes around the blades, creating a vacuum in the blower itself. That allows the blower blades to spin without air friction at part throttle.
 

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Only if it was that easy! Some have tried the boost bypass mod but it not recomended. Look for the the boost bypass mod some where on this forum.
 

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Discussion Starter · #7 ·
SaturnI0Nredline said:
Only if it was that easy! Some have tried the boost bypass mod but it not recomended. Look for the the boost bypass mod some where on this forum.
I know of that mod, tried it myself without success. What I am thinking of trying is disabling said butterfly valve. As soon as I get the vid from jpk I will examine it. People have disabled there TVIS butterfly valve on like toyota engines so maybe it can be done on this. I'm willing to try.
 

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clownhair said:
I know of that mod, tried it myself without success. What I am thinking of trying is disabling said butterfly valve.
That probably wouldn't be a good idea. The valve allows air to bypass the impellers inside the supercharger (no kidding, right?) The point is that, at low RPMs, the supercharger isn't spinning fast enough to be of any benefit. The impellers inside would actually restrict airflow and rob the engine of power.

Now, going the other way, getting more than 12 psi boost I think would require better fuel management (more fuel) through the injectors. So, I wouldn't try that one just yet.
 

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Discussion Starter · #9 ·
Signals said:
That probably wouldn't be a good idea. The valve allows air to bypass the impellers inside the supercharger (no kidding, right?) The point is that, at low RPMs, the supercharger isn't spinning fast enough to be of any benefit. The impellers inside would actually restrict airflow and rob the engine of power.

Now, going the other way, getting more than 12 psi boost I think would require better fuel management (more fuel) through the injectors. So, I wouldn't try that one just yet.
Do we know for certain how big the injectors are? I'm gonna look into this and try and crack it.
 

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first at 1000 rpms the engine make 2psi. <---- HEHE is all I can say the beauty of having a gauge I guess. second you will only get 2 more psi at redline if you bypass it. Third say good by to your milage becuase you are going to be forcing the supercharger to work 100% of the time which makes some crazy heat and noise.
 

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Discussion Starter · #12 ·
goofyguy said:
first at 1000 rpms the engine make 2psi. <---- HEHE is all I can say the beauty of having a gauge I guess. second you will only get 2 more psi at redline if you bypass it. Third say good by to your milage becuase you are going to be forcing the supercharger to work 100% of the time which makes some crazy heat and noise.
who needs good gas mileage?
 

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we need it to still function don't we so when we shift or take our foot off the gas it still has to open and release some of the pressure
 

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johnboy8221 said:
we need it to still function don't we so when we shift or take our foot off the gas it still has to open and release some of the pressure
The only reason you need that valve is for part throttle operation. As far as I know anyway. Old school blowers didn't even have a bypass. If you unhook the valve, you might get a little more boost. You're also gonna get around 12 miles to the gallon. Give it a shot, see what happens!
 

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Discussion Starter · #17 ·
Sp00ner said:
The only reason you need that valve is for part throttle operation. As far as I know anyway. Old school blowers didn't even have a bypass. If you unhook the valve, you might get a little more boost. You're also gonna get around 12 miles to the gallon. Give it a shot, see what happens!
I thought the same thing but I checked it out and according to the info I read the roots SC needs the bypass valve :( makes me sad. I spent a few hours yesterday messing with it and hve 2 conclusions on how to get passed it. Somehow blead the reference line so it dosn't show it is gettiing full bosst and will stay closed, or hack the ecm or some other sort of computer interference device.
 

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clownhair said:
I thought the same thing but I checked it out and according to the info I read the roots SC needs the bypass valve :( makes me sad. I spent a few hours yesterday messing with it and hve 2 conclusions on how to get passed it. Somehow blead the reference line so it dosn't show it is gettiing full bosst and will stay closed, or hack the ecm or some other sort of computer interference device.
Make a voltage clamp (on the map sensor) this is what alot of piggyback tuners due, but it doesnt fix the problem with getting the ECU to accept it. You might end up going lean or even into limp mode. Just because you eliminate the ECU's awareness to being more boost it will NOT add more fuel or compensate the timing to accept it. Not to mention there are two map's and knowing which one if not both to clamp is the question.

A voltage clamp basicly only allows a peak voltage to pass. Most MAP sensors are 0-5 volt, so by limiting it to 0-4.8volt or so it tells the ECU that full boost is not reached even though you may have passed it by several pounds. HOWEVER this does not say that our's is the same.
 

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Sinister redlines said:
Make a voltage clamp (on the map sensor) this is what alot of piggyback tuners due, but it doesnt fix the problem with getting the ECU to accept it. You might end up going lean or even into limp mode. Just because you eliminate the ECU's awareness to being more boost it will NOT add more fuel or compensate the timing to accept it. Not to mention there are two map's and knowing which one if not both to clamp is the question.

A voltage clamp basicly only allows a peak voltage to pass. Most MAP sensors are 0-5 volt, so by limiting it to 0-4.8volt or so it tells the ECU that full boost is not reached even though you may have passed it by several pounds. HOWEVER this does not say that our's is the same.
this sounds like it would work with a stand alone fmu
 

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Sp00ner said:
The only reason you need that valve is for part throttle operation. As far as I know anyway. Old school blowers didn't even have a bypass. If you unhook the valve, you might get a little more boost. You're also gonna get around 12 miles to the gallon. Give it a shot, see what happens!
"That valve" is what limits or even eliminates your boost. Part throttle operation has nothing to do with it. It will either allow boost to build and/or limit maximum boost to approx 12 psi. It can even prevent boost from building at all under certain conditions or when a system fault is detected. I'll just quote the FSM here to insure everyone knows how it works, then people can decide if there are any potential mods
(I have my own theories and have even tried a few things, with some success but...YMMV)

Boost Control System -Theory of Operation (from 2005 FSM)
The PCM controls boost pressure by using the boost control solenoid. The boost control solenoid is normally an open valve. Under most conditions, the PCM commands the boost control solenoid to operate at a 99-100 percent duty cycle. This keeps the solenoid valve closed and allows only inlet vacuum to control the position of the bypass valve. At idle, engine vacuum is applied to the upper side of the bypass valve actuator, counteracting spring tension to hold the bypass valve open. As engine load is increased, engine vacuum is decreased, causing the spring in the bypass valve actuator to overcome the applied vacuum, closing the bypass valve and allowing the boost pressure to increase.

The bypass valve starts to close when the vacuum measures 250 mm Hg (10 in Hg) and is fully closed at 90 mm Hg (3.5 in Hg). When reduced boost pressure is desired, the PCM commands the boost control solenoid to operate at a 0 percent duty cycle. This opens the solenoid valve and allows boost pressure to enter the bypass valve actuator at the lower side to counteract the spring tension, opening the bypass valve and recirculating excess boost pressure back into the supercharger inlet.

Supercharger boost pressure is regulated to prevent engine and drive train damage. When the engine is operating under high boost conditions, the powertrain control module (PCM) limits boost pressure to 83 kPa (12 psi). The PCM disables boost under the following conditions:

• When reverse gear is selected
• When the engine coolant temperature (ECT) is excessively high
• When drivetrain abuse is detected
• When the vehicle is decelerating
• If an intercooler pump failure is detected
• If the intake air temperature (IAT) sensor 2 becomes excessively high
• Under heavy load in first and second gear at engine speeds above 5,800 RPM
Boost System Diagram
(1) By-Pass Valve Actuator
(2) Boost Signal
(3) Boost Control Solenoid
(4) Boost Source
(5) Supercharger
(6) Intake Plenum
(7) By-Pass Valve
(8) Throttle
(9) Air Cleaner
(10) MAF Sensor
(11) Inlet Vacuum Signal
 

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