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I thought I understood how the resonance flap operates, but some things aren't making sense. Looking at this link: http://mmm-five.net/Articles/files/E34M5_IntakeResOverhaul.pdf it explains that it increases torque at less than 4000rpm. The torque curve also confirms this. What doesn't make sense is that when the flap isn't working, due to failed actuator or deteriorated vacuum lines, a loss of torque is noticed. However the actuator is in the extended position (not actuated) below 4000rpm, so I would think you wouldn't notice any difference below 4000rpm if the system wasn't working. I would expect a lack of HP in above 4000rpm with a failed actuator system. What am I missing?
 

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So the actuator is actually closing a valve (throttle plate) in the center of the plenum which serves to lengthen the path that the resonance pulse (caused by the shutting of the intake valves) has to travel (based on the firing sequence of 153624) this allows the pressure wave to influence the charge of the next firing cylinder to a greater extent. Effectively you’re gaining longer runners at a lower rpm. So with the actuator not functioning the valve is left open which causes a loss of torque at lower rpms. It’s all a timing issue, hope this brief response helps.

We’ve been playing with this quite a bit with our new composite plenum, the B36 is easy the B38 moved it to another level!

Please let us know if you need a new actuator or any new components, we’d be happy to help!

Greg | Angry ***
 

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So the actuator is actually closing a valve (throttle plate) in the center of the plenum which serves to lengthen the path that the resonance pulse (caused by the shutting of the intake valves) has to travel (based on the firing sequence of 153624) this allows the pressure wave to influence the charge of the next firing cylinder to a greater extent. Effectively you’re gaining longer runners at a lower rpm. So with the actuator not functioning the valve is left open which causes a loss of torque at lower rpms. It’s all a timing issue, hope this brief response helps.

We’ve been playing with this quite a bit with our new composite plenum, the B36 is easy the B38 moved it to another level!

Please let us know if you need a new actuator or any new components, we’d be happy to help!

Greg | Angry ***
Greg, I think I understand how it works, essentially modifying runner length. But my confusion is that you state "with the actuator not functioning the valve is left open which causes a loss of torque at lower rpms" but a failed actuator or vacuum system WILL leave the valve open at lower RPMs. Maybe it's my definition of torque and "lower RPMs", but I'd consider the operating conditions below 4000RPMs to be relying on torque, and considered low RPM.
Based on your description of the system, it seems more accurate to say the system helps improve HP in higher RPM range (>4000), and that the resonance system (working or not) doesn't affect torque in the the lower RPM range. Does that make sense? I basically want to confirm that the actuator is not supposed to be "energized" before 4000rpm and that my system is not working backwards, because it would make more sense for it to be designed so that it's actuated at low RPM where the is plenty of vacuum available, and to disengage at 4000rpm+WOT.

And I do have the AAS actuator and my system performs the two cycle self test every start!
 

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Greg, I think I understand how it works, essentially modifying runner length. But my confusion is that you state "with the actuator not functioning the valve is left open which causes a loss of torque at lower rpms" but a failed actuator or vacuum system WILL leave the valve open at lower RPMs. Maybe it's my definition of torque and "lower RPMs", but I'd consider the operating conditions below 4000RPMs to be relying on torque, and considered low RPM.
Based on your description of the system, it seems more accurate to say the system helps improve HP in higher RPM range (>4000), and that the resonance system (working or not) doesn't affect torque in the the lower RPM range. Does that make sense? I basically want to confirm that the actuator is not supposed to be "energized" before 4000rpm and that my system is not working backwards, because it would make more sense for it to be designed so that it's actuated at low RPM where the is plenty of vacuum available, and to disengage at 4000rpm+WOT.

And I do have the AAS actuator and my system performs the two cycle self test every start!
So just to be clear the valve doesn’t actually lengthen anything besides the path that the air charge has to travel. So much like an actual intake runner that is longer and narrower aids in torque development at lower rpms due to the same frequency tuning, varying the path the air charge has to travel to the next valve event does the same. Keep in mind when I say air charge I’m referring to the spike in pressure that is a result of intake air hitting the suddenly shutting intake valve. It’s a bit hard to explain without a pic and here is one from BMW describing the system.

F783D5D8-C109-4999-AB9A-3F5BAE5302CE.jpeg

So with the valve failed and not working the air charge from the previous intake event can take a short route to the next valve which causes a loss of torque due to the loss of the proper timing created by the longer path.

For the valve to be actuated two conditions have to be met at different rpms and you must have a healthy vacuum system:
Scenario 1: RPM less that ~4000 rpm and full throttle
Scenario 2: RPM greater than ~6700 and full throttle

To make it even more confusing its possible to use the same charge air events with the same paths as BMW did at more than one switch point to have positive benefits, which you see above. Let me know if you need more information or help diagnosing your issue.

Greg | Angry ***
 

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Discussion Starter #5
So just to be clear the valve doesn’t actually lengthen anything besides the path that the air charge has to travel. So much like an actual intake runner that is longer and narrower aids in torque development at lower rpms due to the same frequency tuning, varying the path the air charge has to travel to the next valve event does the same. Keep in mind when I say air charge I’m referring to the spike in pressure that is a result of intake air hitting the suddenly shutting intake valve. It’s a bit hard to explain without a pic and here is one from BMW describing the system.

View attachment 930214

So with the valve failed and not working the air charge from the previous intake event can take a short route to the next valve which causes a loss of torque due to the loss of the proper timing created by the longer path.

For the valve to be actuated two conditions have to be met at different rpms and you must have a healthy vacuum system:
Scenario 1: RPM less that ~4000 rpm and full throttle
Scenario 2: RPM greater than ~6700 and full throttle

To make it even more confusing its possible to use the same charge air events with the same paths as BMW did at more than one switch point to have positive benefits, which you see above. Let me know if you need more information or help diagnosing your issue.

Greg | Angry ***
Greg, yes, I do believe I understand this concept. I've heard it called "velocity supercharging". Essentially using the inertia of the intake charge to "overfill" the cylinder with more volume than would occur normally.
So that totally explains my misunderstanding. You say the actuator activates BELOW 4000rpm and WOT. Reading another post I read it as ABOVE 4000rpm+WOT, which is why I was confused. Makes perfect sense now that it's a torque boost, and that if your system isn't working, you will lose torque below 4000rpm.
 
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