Hi guys, i'm sure you'll agree with the fact that before attempting to modify something, it is better to understand it ! Here are some good links to read ... maybe some people already know thes facts, but the others one can read it carefully.

1: http://www.tomhenryracing.com/technical/default.htm (Picture at the bottom right of the page)

2: http://www.automotive.eaton.com/prod...erchargers.asp (Point #7)

3: http://www.automotive.eaton.com/prod...s/gm/index.asp (Little picture at the right; Click to see how it works.

4:
http://www.rpmoutlet.com/boost%20bypass.htm (I tried yesterday this modification on my SS/SC, and it doesn't work !!!) This web site could be read to better understand the by-pass valve, but I NOT suggest to do this modification, for many reasons I will expose later.

About what I read and saw on my SS/SC, the mechanical bypass valve (butterfly inside the blower) is normally close (when the engine is shut off).

When the engine idles, the mechanical bypass valve (butterfly) opens to equals the pressure before the blower and after the blower in the intake manifold. (The butterfly is opened by the vacuum bypass motor (actuator), which mechanism can be seen on the outside of the blower; see web site #1). This vacuum motor (which I think is a diaphragm with a spring) is controlled by the vaccum bypass selenoid. This selenoid controls the vaccum pressure coming from the intake manifold. You can see a diagram of all these components in the web site #4; see on the middle of the page and click on the little blue icon wity a white key inside. The selenoid is controlled by the PCM, which "decide" when it's time to activate the selenoid or not.

When you cruise at low speed (no boost required), the valve (butterfly) stay also opened, which prevents the pressure after the blower not to be higher than before the blower, which could be resulting a phenomenon called cavitating.

When the gas pedal is hitted hard (high boost required), the by-pass valve (butterfly) shut off, which cause a increase of pressure in the intake manifold.

Some people on their Ion Redline tried a modification (http://saturnionredline.com/mods.htm) which is clearly written that it is not recommended. This modification is to remove the vaccuum hose that enters the vacuum bypass selenoid and to plug it. The results is that the bypass valve (butterfly) stays ALWAYS closed. Even if it can result in a little higher boost (because you are sure that the PCM cannot control the bypass valve anymore), it's not the desired result. As written before, the main purpose of the bypass valve to keep opened when cruising so it avoids overheating the air entering the blower. It helps also for the gas mileage. It also release the pressure in the intake manifold when you shut off the throttle.

About the kind of modification on the web site #4, I not recommend it. I've personnaly tried it yesterday and IT HAS NOT produce the required result for my Cobalt SS/SC. The modification is to unplug the hose that is between the intake manifold and the selenoid and put in directly in the bypass actuator. The result I experiment is that the vaccum of the intake was always making the bypass valve opened (or partially opened), which cause a non supercharged car (LOL about 120bhp; what a drop of power). It is what i saw on my boost indicator; no boost anymore. (Not saw higher than about 5 PSI). Even with the gas pedal on the floor, the vaccum was not getting as required to close the valve.

As previously written by PSI-FI, the better way is to control all these components by the PCM with a new programmation.

One thing that i've also read (and saw) is that on the vaccum bypass motor (actuator), it has a little Allen Screw that limits the travel at the closed position. On my SS, the screw is nearly unscrewed at the maximum. So I am not sure if the actuator could be more closed. Is that a kind of ON-OFF thing ? Maybe, maybe not. I've read on a web site that sometime it could happen that the screw is not ajusted well. But i haven't try it yet.

At my point of view, simply changing the supercharger pully won't produce the maximum result since the PCM programmation has not be optimised.

Thank you reading me and have a nice day !!!

 

This mod does work, your just not noticing it because your running stock boost levels. I also do not recomend this mod but it does work.

as for new pulleys needing pcm work is crap. The car is capable of handling a couple more lbs of boost without issue. The car in general needs pcm work to fix the AFR's.

 

well, programmation is NOT a word.

but nice try....

 

Thank you for putting our site in your link my name is J.R. Starr and im a sales rep for Tom Henry Chevrolet we're located 20 miles north of Pittsburgh P.A in a small town called bakerstown. Im trying to find out everything i can on staging for the cobalt because im also a silver ss/sc owner. how nice . ill keep you posted on what i come up with.
Thanks for the free ad.

 

The by-pass valve is there to reduce noise (less load) when not needed and economy. It is not necessary to run the blower, Ive said this before. Equalization of pressure in the intake when the engine is not running is to lessen the load on the starter, period.
As far as how the valve works, I believe the cobalts operate differently than the example given. Zinner I believe posted exactly how this works on the SS, try searching for it.

You said you disabled the valve and it didnt work, what exactly did you do because the Harley truck is nothing like what were running. The SS's valve can be disabled by unhooking 1 single vacuum hose and you dont have to plug the switch either. I know this cause I have been running this way for more than 3 weeks, no problems. I was aware of this mod for some time but was leary of it because some have said it will eventualy put the car in limp mode.
However, I ran into someone that has had his valve disabled for months without any problems, so I did it. He reads these threads regularly and if he wants to add to this he will.

DISABLING THE VALVE DOES WORK!!!!!! For how long before a CEL we will see.
Boost at around 2500 is up 4 lbs, max went from 10 to 11.5.
Yes, my fuel economy fell somewhat, especially if your always in the throttle.
I posted about this previously, any one can try this, its as simple as pulling a hose off.
Believe me, your but dyno and the gauge will convince you. It does make a differance and you can feel it.

As far as a ECM reprogamming, its not needed for this mod, your still within the parameters.
Theres been alot of opinions about this so just try it, youll see.

 

Redrocket, the mod I did was exactly like this one linked below ... my car was not pulling good ...

http://www.rpmoutlet.com/boost%20bypassc.htm

 

OK, ive been thinking baout this as I believe what your saying.
Also, I have no reason to say it works if it doesnt, on my SS it makes a differance.

So, heres my theory!!LOL
Alot of guys on here have said that their max boost peeks at 10 psi, including mine.
Question, what is your max boost?
Apperantly the by-pass valve is adjustable(small set screw).

Here it is: what if some of us have their by-pass valves set wrong(the 10 psi guys) and are bleeding boost when we are not supposed to. Then disabling the valve (assuming that the butterfly closes more as no vacuum at all exists) might just give us the boost we sre supposed to have. Hence the added power! Im not saying im getting any more boost than you, im just saying maybe I am now getting what you pretty much already have, thus you dont notice a differance. What do you think?

The problem with this theory is that if the set screw adjusts the butterfly directly, and not the vacuum diaphram, than my theory is wrong. As the lack of vacuum would have little if any effect on the amount the butterfly is open. Maybe someone on the threads(prefferably GM a tech) could educate alot of us on exactly how this works.

Another thing, if the position of the butterfly is not changed by this little trick, than I have to assume that the results I am seeing (gauge) and feeling are because with the valve disabled, all the air coming into the engine passes through the blower all the time. The stock set-up bleeds until no vacuum exists (WOT). If this is true, than you also should notice a differance, maybe not more boost (max) but boost at lower loads than you would have at stock setting.
Because the valve would never bleed, the boost would be directly related to engine RPM.

What does everyone think?

 

My max boost is about 11,5 PSI ... all the things you said (at my opinion) make a lot of sense. In two weeks, i will visit my dealer and will ask a technician to ajust the little screw (I have no allen key). So we'll see if it can make a difference.

A thing that we can do is that : Does someone have is M62 blower out of the car (or the intake tube removed), so he could verify if the butterfly is perfectly closed with his stock screw setup. If not, he could ajust the screw, and tell us which boost he achieve at WOT, before and after the setting.

Have a nice day !

 

Interesting Post.

I've been reading a lot lately about all these bypass valve speculations, but nobody can seem to come to a real conclusion. Some people say the bypass valve "mod" gives more boost, more quickly; others say it's useless and does more harm than good. Without any hard evidence either way, its impossible to figure out.

However, seeing as its just a small butterfly valve in the hull of the supercharger, it really shouldn't be this complicated. I think the answer is that the valve control needs to be addressed through the PCM/ECU as opposed to trying to mechanically adjust it. What we need is a reflash that either adjusts the BPV programming, or allows for a user-controlled bypass valve. With a reflash, we could raise the rev-limiter by a reasonable amount and set the BPV so it doesn't activate until the rev limiter, therefore providing more boost and more power without a pulley change. The LSJ can easily handle a few hundred more RPM, and as we've seen from the dyno graphs, its still building power at redline.

I think it would be really cool if GM released a "Turbo Toys" like setup with the Stage kits. It could allow you to adjust the power level based on the fuel you're using, and allow you to manually adjust the BPV depending on driving conditions. In economy mode, it would stay open almost all the time, allowing for less stress on the engine during cruising and a nice improvement in fuel economy. In performance mode, it would set the BPV to close early and open late, allowing for quicker building of boost and higher PSI levels.

Its just an idea, anyone else think it would be cool??

 

https://www.cobaltss.net/forums/2-0l-lsj-performance-tech-47/adjusting-pass-valve-4369/