Ryephile describes the SC air bypass valve quite well in this posting SC Bypass valve modification

I think this is how it works. Please help me understand where I went wrong in my thinking:

1) If the butterfly valve is open, air flows from the output of the SC back to the input of the SC, reducing the boost.
2) The black hose transfers air between the diaphragm and the intake manifold.
3) When the car is idling, there is a vacuum of sufficient magnitude to suck on the diaphragm and open the butterfly valve, thus effectively "disengaging" the supercharger.
4) When you step "lively" on the throttle, the throttle-body butterfly valve opens, and the vacuum in the intake is lowered.
5) A spring pushes the diaphragm away, causing the bypass valve butterfly to close which "engages" the supercharger again.
6) The diaphragm chamber needs to suck some air from the intake through the black tube in order for the diaphragm to be moved by the spring.
7) Adding a restriction to this tube will slow down the movement of the diaphragm, and therefore the engagement of the supercharger.

The opposite thing happens when coming off throttle. A restriction in this tube will cause the supercharger to remain active for a longer period of time.

It seems like a modification of this sort would produce a lag in the action of the supercharger when hitting the throttle.

Is that the desired effect?

I don't have an MCS, so I can't experiment, and I need some help from you all.

I'm probably COMPLETELY misunderstanding something, so don't expect me to defend this theory frther than I can throw the internet.

I'm thinking a more sophisticated modification would be possible so that there could be different open/close actions depending on which one is the one a user wants to modify.

 

Ideally for performance you don't want a bypass valve; it is implimented on the MCS strictly to improve fuel economy. Removing the bypass valve from the circuit (i.e. Ryephix #1) results in a dramatic loss of fuel economy at the benefit of improved throttle response and essentially instant boost generation. Quickening the bypass valve speed (i.e. Ryephix #2) is a sort of compromise between ideal performance and fuel economy; throttle response almost as good as no-bypass valve and fuel economy somewhere between no valve and stock.

Trippy, from what I can gather, slowing the response (damping) of the bypass valve will improve the smoothness of operation, at the expense of slower boost generation. This loss of transient throttle response I consider a negative performance attribute.

I hope that helps,
Ryan

 

ryephix #2?
1 was the zip tie fix, is #2 the same as the M7 device?
I am actually scared to do a search on ryphix #2
Ben

 

lets see...

Trippy says this:
1) If the butterfly valve is open, air flows from the output of the SC back to the input of the SC, reducing the boost.
2) The black hose transfers air between the diaphragm and the intake manifold.
3) When the car is idling, there is a vacuum of sufficient magnitude to suck on the diaphragm [compressing the spring] and open the butterfly valve, thus effectively "disengaging" the supercharger.

sounds good so far ( I added the [] comment)
Ryphile says this:
Now, this assembly is totally self-contained. The vacuum line goes from the front side of the butterfly to the vacuum diaphragm top piece, which sucks in the Diaphragm. The spring tries to keep the tie-rod pushed out (so the butterfly is closed). I am going to put in a stiffer rate spring, to make the butterfly harder to open per given vacuum. The idea is the bypass valve will tend to stay closed except for very light throttle cruising, coasting/engine braking, and idling (all big vacuum situations).

So the opposing forces are
1) spring -> keeps valve closed => engages supercharger
2) vacuum line -> keeps valve open => dis-engages SC

no revelations here (forgive me for thinking out loud)

so it seems pretty straight forward that a) increasing the spring constant or b) reducing the strength of the vacuum (restricting the line) would achieve the same effect -> keeping the valve closed

I think where you got hung up was between 6) and 7)

7) Adding a restriction to this tube will slow down the movement of the diaphragm, and therefore the engagement of the supercharger.

I dont think this is the right way to say it. you almost make it sound like the diaphragm is driven by the vacuum line (in which case it would be a air/vacuum line both sucking and pushing the diaphragm (spring does all the pushin)).

hope I got that right. hope it helps

Chuck

 

you don't have to do a search, just click the link in Trippy's post above.


_________________

 

Ryefix #2 link.

 

I think I agree with Chuck that the spring should be able to overcome any resistance from the diaphragm that might be caused by a restricted vacuum line.

 

Excellent "thinking out loud" That's exactly how we get to understand each other.

>>so it seems pretty straight forward that a) increasing the spring constant or b) reducing the strength of the vacuum (restricting the line) would achieve the same effect -> keeping the valve closed

I think that these two modifications do very different things.

1) Changing the spring means that you need more vacuum to open the butterfly valve as Ryephine desctibes.
2) Restricting the tube SLOWS DOWN the movement of the butterfly valve.


>>7) Adding a restriction to this tube will slow down the movement of the diaphragm, and therefore the engagement of the supercharger.
>>
>>I dont think this is the right way to say it. you almost make it sound like the diaphragm is driven by the vacuum line (in which case it would be a air/vacuum line both sucking and pushing the diaphragm (spring does all the pushin)).

For the spring to be able to move the diaphragm, air needs to be sucked through the tube.

I think making that tube smaller will make the air flow more slowly, and the spring will move the diaphragm more slowly, and the butterfly valve will close more slowly which will make the supercharger "engage" more slowly.

Does that make sense?

I'm clarifying my thoughts. Your comments were GREAT and you explained your though processes very well. I understood completely.

 

>>I think I agree with Chuck that the spring should be able to overcome any resistance from the diaphragm that might be caused by a restricted vacuum line.

Good thinking here.

If that were the case, how would restricting the tube have any effect on the bypass valve?

I'm very interested, and any ideas will be appreciated.

Don't think that if you disagree with my idea here that I'll attack you.

 

Yes, the spring will overcome a restriction in the vacuum line....over time. The important aspect is the restricted vacuum line acts as a damper, stretching the movement over a time basis, regardless of direction of movement. Basically, the diaphram IS "driven" by the vacuum line; the diaphram can only move as fast as both the spring and the vacuum line allow.

cdconsor - you're not reducing the "strength" of the vacuum line with the restriction, just it's displacement capability.

 

>>Ideally for performance you don't want a bypass valve; it is implimented on the MCS strictly to improve fuel economy. Removing the bypass valve from the circuit (i.e. Ryephix #1) results in a dramatic loss of fuel economy at the benefit of improved throttle response and essentially instant boost generation. Quickening the bypass valve speed (i.e. Ryephix #2) is a sort of compromise between ideal performance and fuel economy; throttle response almost as good as no-bypass valve and fuel economy somewhere between no valve and stock.
>>
>>Trippy, from what I can gather, slowing the response (damping) of the bypass valve will improve the smoothness of operation, at the expense of slower boost generation. This loss of transient throttle response I consider a negative performance attribute.
>>
>>I hope that helps,
>>Ryan

Ryan,

It is actually implemented for two different reasons. One being fuel economy, the second is take the load of hot air off the engine cylinders while decelerating. A lot of superchargers are lower boost 5-7psi. In this situation the bypass is not needed as much because of the lower boost, and you do not always find a bypass valve on supercharger used in these scenarios. The Eaton in the MCS is a high boost device in the @15psi range or higher if you have the JCW. In these applications a bypass valve is used. The main reason for this is to cause the hot pressurized air to escape. This is the primary reason in this scenario. Not the gas mileage. Both Eaton and Magnuson say that you will cause harm to the supercharger and/or engine by removing the bypass valve on this application. Therefore the operation of the bypass valve is critical to the longevity and reliability of the supercharger. Magnuson has stated this not from a warranty or speak the manufacturer talk, but from a tuning perspective as well, since they do perform tuning services on the Eaton supercharger. If both of these companies say do not remove this valve, or you will cause damage, then mileage is not the main issue but the longevity of the Supercharger. If removing the valve will cause damage, then the same is true but to a lesser extent if you impair it's function. The M7 device enhances one feature of the bypass valve, but in my opinion it impairs the critical function of the bypass valve. The critical function is to cause hot compresses air to escape.

The restriction from the M7 device, closes the valve much quicker, because it lessens the impact of the vacuum has on the valve. With the valve closed boost is obtained quicker, thereby giving you a sense of quicker throttle response. When you deccelerate, the impact of the vacuum on the valve to open is also impaired, therefore it stays shut longer, causing the gases and hot air to continue their path into the cylinders.

The reason why I feel this has a greater impact to the SC/Engine than say a pulley, is that a pulley is still performing an acceptable design function of the supercharger.
It is still rotating the supercharger in the same direction under the same scenarios. While it does spin faster, and it will cause some wear on the supercharger, it is not going against the design principles of the supercharger. This can be further enforced by the fact that a smaller supercharger pulley is installed on the JCW and comes with a full factory warranty. No way would BMW place a factory warranty on a part that was outside of the specifications from the manufacturer. Whereas changing the tube on the bypass valve is actually changing the design function of the valve. The valve is intended to close on acceleration and open on deceleration. The tube is impairing it's ability to open on deceleration. While it has a neat desired affect of closing quickly, it is being done at the expense of opening quickly. And that is the problem of a cheap simple solution for this type of a problem. The better solution would be to allows something to close the valve quickly, but still maintain the ability to open just as quickly.

 

> (restricting the vacuum line) , closes the valve much quicker, because it lessens the impact of the vacuum has on the valve.

Could you explain this more for me?

As I understand it,

1) A spring is holding the bypass valve closed "engaging" the supercharger..
2) Vacuum from the intake manifold sucks the air our from behind the diaphragm, pulling on it, compressing the spring and causing the butterfly valve to open and "disangaging" the supercharger.
3) When you step on the throttle, the pressure in the intake manifold goes "up" and some air leaks through the tube, allowing the spring to push the diaphragm, and allowing the butterfly valve to close "Engaging" the supercharger.

Restricting this tube will cause the supercharger to "engage" more slowly not more quickly.




> The tube is impairing it's ability to open on deceleration.

This I agree with.

I'm just not seeing how the restriction allows the valve to open faster, but close more slowly.

I don't see why there would be a difference.

Again, I reassure you I am after understanding, NOT agreement with my idea.

 

Magnuson makes no mention of recycling boost as a form of required longetivity measure due to "hot air", but an improvement in fuel economy and parasitic power loss: Magnuson on Bypass Valves

Eaton also makes no mention of "hot air" needing escape: Eaton technical brief

The only thing I found that mentions heat as a concern was on an SVT Lightning page, where they mention rotor cavitation. I have yet to hear anything about the M45 cavitating.

I also don't understand how a vacuum line restriction can cause assymmetrical performance of the bypass valve (i.e. open quicker, but close slower). The line dampning is there no matter what!

 

I have been working on a fix that shows some promise, but due to the scarcity of the parts I am using, it's not ready for prime time (sound familiar? ).

Basically I am using vacuum control valves that were common in late 70s cars and used in various parts of the emission control system. These little valves work similar to check valves, but with a twist. The valve will allow more or less unimpeded flow in one direction, and a slow flow in the other. The valves were used in various ways to slow some aspect of engine control in one direction, for example, allowing for a slow vacuum advance to prevent knocking at part throttle but allow for a quick return to a retarded condition at full throttle. THese days such functions are performed by the ECU software, not with hoses and valves and tubing which deteriorates over time.

My implementation of the control valve in the case of our beloved supercharger bypass valve is to allow the airflow to the diaphragm chamber to move unimpeded, and the airflow from the diaphragm chamber to be slowed. In other word, when in a low vacuum or boost situation is called on (stomp on the gas) the control valve allows ambient air pressure (and boost) to enter the diaphragm chamber to quickly close the valve, but acts also to slow the reopening of the valve right away.

It might be a little easier to think of this kinda like a door closer on a screen door, but installed backwards. It allows the door to slam shut, but offers a slowing resistance to the door being opened again, opposite of how it would normally work.

The net effect of this control valve on the bypass valve operation would be more or less like a shock absorber on a spring; it will dampen the effects of any pressure oscillations, and actually have a closing effect on the bypass valve in the presence of pressure oscillations. It works well in theory.

My problem in putting it into practice in what one would expect in using previously used, 25+ year-old parts. Many arent in the best of shape, and of the two valves I have now, only one works even remotely well. The inside workings of the valves are made of rubber, and this has hardened up over time. I am trying to locate a similar type of valve that can be purchased today, as none of these valves have a useable part number (and I am not certain which car these came from originally). Give me some more time to do a bit of research on this, and do some testing (yes, it does dampen out the yo-yo considerably) and I will post my findings. No self addressed, stamped envelopes needed.

 

Ryan,

I talked to someone at Magnuson about the valve, but I am trying to find the communication. Here is what I found on the net:

http://www.mn12performance.com/mn12-...e/scintake.htm
http://www.kennedysdynotune.com/More%20FAQs%201.htm
http://www.mustang50magazine.com/tec...41/index1.html
http://www.gadgetonline.com/Super.htm
http://www.timskelton.com/lightning/...ost_bypass.htm

Here is another article explaining the general ideas behind the bypass valve:
http://www.superchargersonline.com/content.asp?ID=14

I could only find references to Eaton and Magnuson stating that a bypass valve on a supercharger improves fuel economy. None of the documents listed above make that mention. I agree that it will help fuel economy, I just think that is marketing speak for the companies. Our engines are running at a fairly high rate of boost for a Supercharger. Most people are seeing between 15psi-19psi depending on mods. This is pretty high when most people only run in the in the 78-10psi (i.e the new Miata for a 4-cylinder example). So I think at 17-19psi it is important to relieve the pressure.

Restriction of the vacuum line cause symmetrical performance of the bypass valve. When accelerating the vaccum is decreased closing the valve. When you decelerate or idle the vaccum is increased in the line opening the valve. By placing a restriction in the line, when you accelerate, the restriction will cause the vacuum to have less of an affect, so the valve will shut quickly. Not as much vacuum holding it in place. When you decelerate, and vacumm tries to restore itself, the restriction in the line will decrease the amount of "pull" on the valve keeping it closed longer until vacuum builds up.

 

>>Restriction of the vacuum line cause symmetrical performance of the bypass valve.

I agree with this as do several other posters.

>> When accelerating the vaccum is decreased closing the valve.
>>When you decelerate or idle the vaccum is increased in the line opening the valve.

This is also in line with what I think is hapenning.


>>By placing a restriction in the line, when you accelerate, the restriction will cause the vacuum to have less of an affect, so the valve will shut quickly. Not as much vacuum holding it in place.

I disagree here. If you were to put a vacuum measuring device into the suction-side of the diaphragm and measure the pressure when the car is idling you would see that the pressure (Less than atmospheric) is IDENTICAL in the restricted tube and the non restricted tube versions.

The restriction does not change the steady-state pressure on the other side of the restriction. I only changes the speed at which the pressure changes.

>>When you decelerate, and vacumm tries to restore itself, the restriction in the line will decrease the amount of "pull" on the valve keeping it closed longer until vacuum builds up.

This one I once again agree with.


So first you said the restriction will make the action of the valve symmetric whith which I agree.

Then you describe a non-symmetric valve actuation with wich I disagree.

I think you are thinking that the restriction will change the pressure at the diaphragm-end of the tube right?
It will not do that in a steady-state. What I mean by that is that if the car is idling for 5 seconds or so, the pressure at the diaphragm-end of the tube will be the same as the manifold-end of the tube.

How can I explain it a little more clearly?

I know, let's take a baloon example:

Blow up a baloon. (No, REALLY, I'll wait.......................)
OK, now insert a tube into the neck of the baloon.
Time how long it takes for the baloon to empty. Well? How long did it take?
Let's say 15 seconds OK?
The pressure on both sides of the tube are equal now right?

Blow up the baloon again. This is the last time, I promise.
Now, insert a restriction into the tube.
OK, now insert a tube into the neck of the baloon.
Time how long it takes for the baloon to empty. Well? How long did it take?
Let's say 30 seconds OK?
The pressure on both sides of the tube are equal now right?

So the restriction didn't cause the balloon to stop emptying part way empty as it would have if the pressures were not equal, it just slowed down the emptying.

There will not be a test, and I will try a better explanation if there is still doubt about it.

 

FWIW, the M45 application for the Miata (6-7lbs boost) also uses the bypass valve, so it's not only used in high boost applications.

 

You want to make the valve react more quickly? Put a BIGGER line from the valve to the intake manifold. Want to get rid of the valve but still get rid of the hot air? How about a pop-off valve or wastegate. You could even put a whistle on it to let you know when its working and impress your friends(Picture whistling MINIs at an Auto-X).

 

pretty good balloon analogy (I'm dizzy now by the way) but its not really the same scenario as what is happening in the car.

you'd need to measure time to blow up the balloon and compare it to time to let it deflate.

What I mean by this is that when the balloon deflates it has 1atm working on it (both for open and restrictred cases) when you blow it up, who knows how much lung pressure you can generate. My point is that airflow is governed by restriction as well as source pressure.

ok now this is where my lack of engine knowledge trips me up so let me pose a question. What is the source of vacuum to the line? What is the source of pressure? does it have the same (for lack of a better word) magnitude? If not then you can get asymmetric behaviour.

Lets sort this out

Chuck



_________________
Motorin' ... right now!

 

>>What I mean by this is that when the balloon deflates it has 1atm working on it (both for open and restrictred cases) when you blow it up, who knows how much lung pressure you can generate. My point is that airflow is governed by restriction as well as source pressure.
>>
>>ok that this iw where my lack of engine knowledge trips me up so let me pose a question. What is the source of vacuum to the line? What is the source of pressure? does it have the same (for lack of a better word) magnitude? If not then you can get asymmetric behaviour.


Oh, now we are getting somewhere. I like this direction.

Yeah, the pressure difference between one end of the hose and the other will hava an effect on the flow.

So, we need to know a few pressures for the intake manifold.

1) Pressure at idle.
2) Pressure when stepping on the throttle aggressivly.
3) Pressure after releasing the throttle, during engine decelleration.

Andy? do you have some of these at all?

I can certainly see how we could get an asymetric open/close TIME even with a fixed restriction. Good call.








If I could go back to this question for a second:

> who knows how much lung pressure you can generate

I'd like to say that the vote seems to be 50% Trippy Sucks and 50% Trippy Blows, so it all evens out in the end.
_________________
Team: Rational thought

 

as i sit hear and read all of this, even though i understand it all, i keep wanting to say, "but what if the world spins in the other direction? what will happen then?"

_________________
"The Chad" ~ EB/B S with Aero Kit. http://www.michiganmini.com
http://www.detroittuned.com who wants to go faster?

 

Eric,

Yes other applications use the bypass valves, even the Miata, but it is especially needed for high boost applications. Some 5psi chargers use it as well.

Trippy,

It is the same vacuum, but with less force. Take your vacuum cleaner hose and turn on your vacuum cleaner. Then put a DVD case over it that has some weight, then tilt it upside down. The vacuum will hold the DVD case in place. Then tape over the hole with masking tape so that only 10% of the hole is open. Turn on the vacuum cleaner and try to lift the same DVD case. You can't do it because I just tried it. My wife was wondering what the heck I was doing. The tape acts as the restriction and think of the DVD case as the valve. If I was to continue to increase the vacuum it would eventually lift the case. In the scenario where there was no tape the DVD case lifted immediately with very little vaccum. When I put the restriction on the vacuum had to build before the case lifted off.


This is the same for the valve. With no restriction more force is needed to pull the valve shut, or more vacuum pressure has to be decreased. With the restriction in place, it the vacuum pressure has to build to a greater value to open the valve.

 

>>It is the same vacuum, but with less force. Take your vacuum cleaner hose and turn on your vacuum cleaner. Then put a DVD case over it that has some weight, then tilt it upside down. The vacuum will hold the DVD case in place. Then tape over the hole with masking tape so that only 10% of the hole is open. Turn on the vacuum cleaner and try to lift the same DVD case. You can't do it because I just tried it.



But you didn't do it quite right.

I agree that your experiment would produce the results you saw, but PLEASE try this experiment if you have time.

If you have two plastic extensions for your vacuum cleaner, put them on, turn on the vacuum and pich up a Book and CD case to measure the force.

Then tape the end of one of the extension tubes up until it is almost completely closed, and insert that end into the other extension tube.

The second extension tube has the normal size opening which you try to pick up the CD case and book.

If you get a proper seal against the book or CD case, you will be able to pick both of them up with the restricted and unrestricted hose. With the unrestricted hose, you can immediately pick the object up, with the restricted one, you have to wait several seconds for the air to be sucked out of the second extension.

If you have air leaking around the CDcase-to-hose end, you will not be able to pick them up with the restricted hose though.

That is a superb experiment, and everyone can try it at home to verify that the restriction in the middle of the tube will NOT reduce the vacuum's power to lift objects.

Excellent. Even if it eventually shows the opposite of what you were trying to show. Thank you.

 

Trippy,

I agree with you. The restricted one takes longer because the vacuum has to build up. The same holds true for the bypass valve. It takes longer to open the valve because of the restriction.

 

I still say a servo control unit would be the way to go.