Installing a MBC using BOTH external wastegate ports?

99gst_racer · Apr 9, 2007

I was shopping for a new MBC on eBay and I stumbled across this image.

Can anyone explain why it would be better to have the lower port plumbed into the mix? Is there a benefit to sending a pressure source to the lower port as well? Please explain.

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wishihadatalon · Apr 9, 2007

If that is like a Tial gate at all then the lower(side) port is the one you send signal to to lift the valve.

http://tialsport.com/documents/w3_tial_wginstall.pdf Using both ports is the way you are supposed to do it according to Tial. For some reason this doesn't make sense to me because the pressure signal is going to lift the valve and you will never reach a pressure high enough do anything with the mbc.

I think you are only supposed to use both ports with an ebc because you can switch the signal. Sending the signal to the top port to hold the valve closed as long as possible and then switch to the side port to inflate the diaphragm and lift the valve enough to control a set boost level.

oldman · Apr 11, 2007

The Tial instruction is for an EBC/bleeder MBC setup, with a ball/spring MBC, you're suppose to use just the side port with the top port VTA or capped off.

VelocitàPaola · Apr 11, 2007

I don't know Bruce... look at those instructions, it says "manual air regulator or electronic air control valve."

Paul #2, I've seen TiALs and other two-port external wastegates with an MBC connected to both ports. My theory is that it'll allow you to run higher boost with a smaller spring. I have a feeling the ball/spring type MBCsm and even bleeder-type MBCs, will only allow you to accurately raise boost so much before you need to get a larger spring. By using a dual port MBC rig, I think you can get away with a smaller spring.

TimG · Apr 11, 2007

It's a very simple concept and I've seen it and will run it this year.

The top port is used as an "air spring". The air is regulated in terms of PSI by the air pressure regulator. If there is 2 psi going to the top port (regulated through the air pressure regulator) and a 10psi spring in the gate, you will need to send a signal of 12psi to the lower gate port in order to open the total spring + "air spring" pressure, therefor you will have 12 psi.

If you have the the air pressure regulator set for 10psi (top port) and you have a 10 psi spring (top port), you will need something > then 20 psi going to the lower port to open and gate and concequencely run 20psi.

20psi allowed to enter the top chamber + 10psi spring = 30psi to bottom port to open the gate... etc

oldman · Apr 11, 2007

Trust me Paul #1, I have done alot of research on this and I have a brand new TIAL 44 from Extreme PSI sitting right in front of me with instructions to use only the side port and VTA the top port with MBC, on the top of the instruction sheet there is a *NOTE* For electronic boost controller installation, use the manufacture's instruction.

Let's break it down into different situations for better understanding.

1. With both ports open, much like leave the fitting on an internal wastegate fitting open, the wastegate is suppose to hold approximately 2x the spring pressure (its ability to hold back exhaust pressure). Example, 14psi spring = 28ish psi of intake pressure.

2. No boost controllers but both top and bottom connected to straight intake pressure, the result is the same as #1, 28psi.

3. No boost controller but with side port connected to intake pressure signal and top port VTA, much like running no MBC with an internal wastegate, the wastegate will hold exact the spring pressure. Example 14psi spring = 14 psi of intake pressure.

4. EBC or bleeder MBC, side port sees intake pressure (which will result in #3), the outlet of EBC or bleeder connects to the top port, for every psi the top port sees, there is one PSI increase in intake pressure. Note, a bleeder MBC will work in reverse in adjustment as in an internal gate environment, the more pressure you bleed off, the less the top port sees, the lower the boost level.

5. Ball/spring MBC, top port VTA and outlet of MBC connects to the side port. No pressure will be sent to the side port until the spring pressure in the MBC is overcomed, just like an internal setup. The reaon a ball/spring MBC doesn't work with the top port is because you have no control over exactly how much pressure to send, either you get nothing or you get everything, unlike an EBC or bleeder MBC. Let's put it in examples of running a ball and spring mbc using the TIAL instruction, assuming the wastegate spring pressure is 14psi.

A. MBC all the way out (no pressure on the ball), top and bottom port sees the same pressure, you get #2, 28psi.

B. MBC all the way in (max pressure on the ball), nothing gets sent to the top port, you get #3, 14psi.

So far so good but the problem is contolling boost pressure in between.

C. MBC set to anything between 0-14psi, as soon as the ball gives, the top port will immediately see the same pressure as the side port, you'll always get #2, 28psi.

D. MBC set to anything 14psi+, the top port will never see anything at all because the side port will open the wastegate before the ball is overcome, you'll always get #3, 14psi.

Hope my explanation isn't too confusing.

Lastly, to get away with using a smaller wastegate spring while trying to run higher pressure, you leave the side port open, 28psi, then for every psi you add to the top port, you get 2psi more in intake pressure.

99gst_racer · Apr 11, 2007

OK, it's starting to make much more sense now. Thanks for the clarification guys.

I just want to make sure I have it right then. I will have 20psi of spring pressure in my wastegate, and I'll be using a ball and spring MBC. So, I would plumb it into the lower port on the Tial, and leave the upper one alone? Is that correct? If so, would it be OK to plug off the top port?

TimG · Apr 11, 2007

99gst_racer said:
OK, it's starting to make much more sense now. Thanks for the clarification guys.

I just want to make sure I have it right then. I will have 20psi of spring pressure in my wastegate, and I'll be using a ball and spring MBC. So, I would plumb it into the lower port on the Tial, and leave the upper one alone? Is that correct? If so, would it be OK to plug off the top port?

That will work but leave the top port vented to the atmosphere. Don't plug it or else you will create a pressure increase in the top half of the diaphram and it won't control boost like you want.

oldman · Apr 11, 2007

99gst_racer said:
I will have 20psi of spring pressure in my wastegate, and I'll be using a ball and spring MBC. So, I would plumb it into the lower port on the Tial, and leave the upper one alone?

Correct, with a ball and spring MBC, pretend that the top port doesn't even exits and treat as if it's a internal wastegate actuator, boost control is done strictly through your MBC. With that said, the spring in the MBC becomes the breaking point so make sure you have a heavy spring in your MBC if you planing on running high boost levels that can withstand the boost level. Also, make sure that the ball/spring you choose is an well designed/constructed one where pressure doesn't leak around the ball before the spring is overcome, or else the whole equation will change drastically.

Is that correct?

Yes.

If so, would it be OK to plug off the top port?

Yes, for the purpose of preventing dirt from entering the top chamber.

Also keep this in mind, to run higher boost levels than the maximum allowed by the wastegate spring (2 X 20PSI = 40PSI) without upgrading to a heavier wastegate spring like my last comment addresses on the previous post,

Lastly, to get away with using a smaller wastegate spring while trying to run higher pressure, you leave the side port open, 28psi, then for every psi you add to the top port, you get 2psi more in intake pressure.

you will need a bleeder type MBC, your ball and spring will not work for the same reasons cited above. If you plan to run more than 40psi and you have not purchase the ball and spring yet, this is one of the few exceptions where a bleeder MBC might be a better option.

oldman · Apr 11, 2007

TimG said:
That will work but leave the top port vented to the atmosphere. Don't plug it or else you will create a pressure increase in the top half of the diaphram and it won't control boost like you want.

Tim, are you suggesting that pressure will leak from the bottom to the top chamber through the diaphram? I have not installed my TIAL yet but this was one of the things on my check list. If in fact it will leak, definitely leave the top port VTA.

TimG · Apr 11, 2007

oldman said:
Tim, are you suggesting that pressure will leak from the bottom to the top chamber through the diaphram? I have not installed my TIAL yet but this was one of the things on my check list. If in fact it will leak, definitely leave the top port VTA.

It won't leak. Think of the gate as a two way diaphram. If you have one handy, take the spring out, put your thumb over top of the top port and try to push the gate open with one of your other fingers. The air in the top chamber has no where to escape too and just creates more pressure within the top chamber, making it very hard to open the gate.

If you vent the top port (top chamber) off to the atmosphere, it will vent and intake air as needed and run completely off the spring and boost pressure to the lower port.

oldman · Apr 11, 2007

TimG said:
It won't leak. Think of the gate as a two way diaphram. If you have one handy, take the spring out, put your thumb over top of the top port and try to push the gate open with one of your other fingers. The air in the top chamber has no where to escape too and just creates more pressure within the top chamber, making it very hard to open the gate.

Make sense. :thumb:

99gst_racer · Apr 11, 2007

I'll be pulling my springs out and installing a large and small blue. That will net me around 20 psi on my 44mm. I'll be using the ball & spring MBC to get the boost up to around 26ish from that point.

I'll just install a banjo on the top port and leave it un-capped (should help with keeping dirt out). And I'll just use the side port for my MBC. Thanks again for all of the clarification, guys.

wishihadatalon · Apr 11, 2007

oldman said:
Trust me Paul #1, I have done alot of research on this and I have a brand new TIAL 44 from Extreme PSI sitting right in front of me with instructions to use only the side port and VTA the top port with MBC, on the top of the instruction sheet there is a *NOTE* For electronic boost controller installation, use the manufacture's instruction.

Let's break it down into different situations for better understanding.

1. With both ports open, much like leave the fitting on an internal wastegate fitting open, the wastegate is suppose to hold approximately 2x the spring pressure (its ability to hold back exhaust pressure). Example, 14psi spring = 28ish psi of intake pressure.

2. No boost controllers but both top and bottom connected to straight intake pressure, the result is the same as #1, 28psi.

3. No boost controller but with side port connected to intake pressure signal and top port VTA, much like running no MBC with an internal wastegate, the wastegate will hold exact the spring pressure. Example 14psi spring = 14 psi of intake pressure.

4. EBC or bleeder MBC, side port sees intake pressure (which will result in #3), the outlet of EBC or bleeder connects to the top port, for every psi the top port sees, there is one PSI increase in intake pressure. Note, a bleeder MBC will work in reverse in adjustment as in an internal gate environment, the more pressure you bleed off, the less the top port sees, the lower the boost level.

5. Ball/spring MBC, top port VTA and outlet of MBC connects to the side port. No pressure will be sent to the side port until the spring pressure in the MBC is overcomed, just like an internal setup. The reaon a ball/spring MBC doesn't work with the top port is because you have no control over exactly how much pressure to send, either you get nothing or you get everything, unlike an EBC or bleeder MBC. Let's put it in examples of running a ball and spring mbc using the TIAL instruction, assuming the wastegate spring pressure is 14psi.

A. MBC all the way out (no pressure on the ball), top and bottom port sees the same pressure, you get #2, 28psi.

B. MBC all the way in (max pressure on the ball), nothing gets sent to the top port, you get #3, 14psi.

So far so good but the problem is contolling boost pressure in between.

C. MBC set to anything between 0-14psi, as soon as the ball gives, the top port will immediately see the same pressure as the side port, you'll always get #2, 28psi.

D. MBC set to anything 14psi+, the top port will never see anything at all because the side port will open the wastegate before the ball is overcome, you'll always get #3, 14psi.

Hope my explanation isn't too confusing.

Lastly, to get away with using a smaller wastegate spring while trying to run higher pressure, you leave the side port open, 28psi, then for every psi you add to the top port, you get 2psi more in intake pressure.

You worded that much better than I ever could. I was trying to explain it like that but I don't think it was quite the same.

VelocitàPaola · Apr 11, 2007

oldman said:
Trust me Paul #1

I like that I'm finally being referred to as "Paul #1" around here.

oldman said:
2. No boost controllers but both top and bottom connected to straight intake pressure, the result is the same as #1, 28psi.

oldman said:
4. EBC or bleeder MBC, side port sees intake pressure (which will result in #3), the outlet of EBC or bleeder connects to the top port, for every psi the top port sees, there is one PSI increase in intake pressure. Note, a bleeder MBC will work in reverse in adjustment as in an internal gate environment, the more pressure you bleed off, the less the top port sees, the lower the boost level.

I think I see what you're saying here, Bruce, but could you clarify these two points?

oldman · Apr 11, 2007

2. No boost controllers but both top and bottom connected to straight intake pressure, the result is the same as #1, 28psi.

When the top and bottom chambers see the same pressure, the two forces cancel each other out as if nothing is connected to either port, at this point the only acting force is the spring pressure pushing down and only way the wastegate will ever open is when the exhaust pressure is great enough to physically push the valve open. This required force is estimated to be reached approximately when the intake pressure is at 2 x the wastgate spring pressure, this is only an estimation however and will vary from car to car because exhaust pressure present depends on the VE of motor and turbine and the required force is dependent of the surface area of the valve itself.

4. EBC or bleeder MBC, side port sees intake pressure (which will result in #3), the outlet of EBC or bleeder connects to the top port, for every psi the top port sees, there is one PSI increase in intake pressure. Note, a bleeder MBC will work in reverse in adjustment as in an internal gate environment, the more pressure you bleed off, the less the top port sees, the lower the boost level.

Let's use Paul #2's 20psi spring as example, if intake pressure source was connected to the side port, it will take exactly 20psi to open the gate, from that point on, for every psi you add to the top port, you a add 1psi to the spring pressure, just like what Tim's post said.

VelocitàPaola · Apr 11, 2007

oldman said:
Let's use Paul #2's 20psi spring as example, if intake pressure source was connected to the side port, it will take exactly 20psi to open the gate, from that point on, for every psi you add to the top port, you a add 1psi to the spring pressure, just like what Tim's post said.

Ya know... I don't know what I was thinking. I understood the first point perfectly already; sorry to have made you type more than necessary. Hopefully it'll be good clarification for others.

But! I obviously trust and respect your knowledge and research; but let me just throw this out there for your consideration. I don't believe ball/spring type MBCs just open at a set point... there must be a gradient between fully "open" and fully "closed." I base this belief on Hooke's Law, and the fact that springs require progressively greater amounts of force to push them past their equilibrium points.

In other words, the force required to compress a spring 2mm is proportionally greater than the force required to compress it 1mm. Thus, there must be some sort of half-way points in between open and closed in a ball/spring MBC.

So, if you were to take one of these MBCs and connect it to a WG in the two-port configuration mentioned above, it should proportionally open to allow excess pressure into the upper chamber to counteract the spring pressure in the lower chamber, no?

Again, just something to think about...

oldman · Apr 11, 2007

VelocitàPaola;151169994 said:
In other words, the force required to compress a spring 2mm is proportionally greater than the force required to compress it 1mm. Thus, there must be some sort of half-way points in between open and closed in a ball/spring MBC.

Even if this is true, the duration of this "half way point" will not be long enough to make much of a difference, we are talking about pressure and not airflow, when we use the term "open", we are refering to when the ball leaves the seat (not how far you compress the spring), both chambers will immediately work to eqaulize in pressure. Furthermore, using Paul's 20psi spring as an example and his MBC is hooked up via the dual port, how would you go about setting the boost level to 26psi? You can't because the side port will always open the wastegate at 20psi, unless your "half way point" starts way before 20psi.

VelocitàPaola · Apr 12, 2007

oldman said:
unless your "half way point" starts way before 20psi.

I always thought it would... but otherwise, good information! Point taken...

oldman · Apr 12, 2007

VelocitàPaola;151170220 said:
I always thought it would

Educate me Paul, don't just leave it at that. Are you saying that if the MBC spring is set to withhold 26psi, PARTIAL pressure will start to get past the ball way before? If so, why? How do you determine when and how much, does it start leaking immediately? If this is true, it would go against the concept of a ball and spring MBC but I'm always up for learning, and I say that sincerely.

Maglin · Apr 14, 2007

oldman said:
Educate me Paul, don't just leave it at that. Are you saying that if the MBC spring is set to withhold 26psi, PARTIAL pressure will start to get past the ball way before? If so, why? How do you determine when and how much, does it start leaking immediately? If this is true, it would go against the concept of a ball and spring MBC but I'm always up for learning, and I say that sincerely.

Thats pretty easy. If the amount of force required to move the ball from the seat was exactly 26 PSI then when the balls moves it's only going to be by a very slight amount which won't let enough air past to actuate the actuator/wastgate. So the actual amount of force to start moving the ball from it's seat would have to be much lower than the desired boost pressure. So once the ball has moved enough to let the actuator/wastegate move it will start to reroute the exhaust around the turbo.

What I don't get is this. I have 2 Tial 44's and a 40 in my garage on a shelf. The 40 has a 8 pound spring in it and one 44 has a 10 and the other a 15 pound spring. On the 40mm wg I have to press really hard to get the valve to actuate. I'm sure far more than 16 psi. And I'm exerting so much force on either 44mm wg to get the valve to move that I can't see if it is even moving. But as soon as I hook a vac pump to the top port I can actuate it and it works as it's supposed to.

So I figured I could get away with only a 1 bar spring in my race car that I'm looking to run 45+ PSI. If your corect then I would have to have at least a 22.5 lbs spring in to run 45 PSI and wouldn't even need to bother with any boost controller. It's interesting to know and I'm going to try that out on my buddies car. Putting a 38mm Tial on with a 1 bar spring. Once I have the EMS tuned for 30 PSI I'll do a pull with no vac on the wg.

oldman · Apr 14, 2007

Maglin said:
Thats pretty easy. If the amount of force required to move the ball from the seat was exactly 26 PSI then when the balls moves it's only going to be by a very slight amount which won't let enough air past to actuate the actuator/wastgate. So the actual amount of force to start moving the ball from it's seat would have to be much lower than the desired boost pressure. So once the ball has moved enough to let the actuator/wastegate move it will start to reroute the exhaust around the turbo.

Then the question becomes how long is this transition time? Is it long enough and the amount of leakage precise enough to make a difference so that a ball and spring MBC can be used through the top port like the TIAL diagram suggests.

What I don't get is this. I have 2 Tial 44's and a 40 in my garage on a shelf. The 40 has a 8 pound spring in it and one 44 has a 10 and the other a 15 pound spring. On the 40mm wg I have to press really hard to get the valve to actuate. I'm sure far more than 16 psi. And I'm exerting so much force on either 44mm wg to get the valve to move that I can't see if it is even moving. But as soon as I hook a vac pump to the top port I can actuate it and it works as it's supposed to.

By adding vacuum to the top port, you're reducing the spring rating. Also keep in mind that 16psi of intake pressure doesn't equal to 16psi of exhast pressure, it's exhaust pressure that pushes on the valve surface, not intake pressure.

Maglin · Apr 20, 2007

oldman said:
By adding vacuum to the top port, you're reducing the spring rating. Also keep in mind that 16psi of intake pressure doesn't equal to 16psi of exhast pressure, it's exhaust pressure that pushes on the valve surface, not intake pressure.

I understand that. It's why I don't see the WG opening due to back pressure cause it would be so great and would definitly be showing some major effects on combustion. I'm putting a bleeder MBC on the top port of my buddies 44mm Tial on his 3rd gen RX7. It is supposed to work and control boost fairly well. I can't get him to spend the money for a EBC, but he has no problem dropping 7 large for a single turbo set-up and street ported motor. It's amazing how cheap some people are when it comes to the fine details.

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Installing a MBC using BOTH external wastegate ports?

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