Exhaust bypass valves explained

[torque124]

Did the dealer remove or modify you exhaust to meet Romania/EU noise limits?

I don't think he has a GT350 yet, correct Andrei ?

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[torque124]

Hi friends,

I have yet to see the GT350 in action.

Here is the proof

 

[AndreiD]

I don't think he has a GT350 yet, correct Andrei ?

At first no man. The car wa so gutted I could swear I got fucked...

 

[shelbyman]

All I know is that I don't know exactly how it works..:shrug: But what I do know is if I put the car in sport mode by selecting that on the right side of the steering wheel the exhaust switches to "track only" on my readout on my center screen between the tach and speedo. Now I can also leave the ride in normal mode and go and change the setting with the switches on the left hand side of the steering wheel and put the exhaust in the loud or track mode that way. I presume I'm still in the normal ride mode doing it that way. The ONE thing I know is when I change the exhaust to track mode I am HAPPY and when its quiet I'm NOT HAPPY...:lol: Don't know what I would have done if the car didn't sound like it does...but glad Ford figured it out

 

[krt22]

A current limited diode would be like a pressure relief valve, which I suspect is not present in the GT350 exhaust. No, Fluid Mechanics dictates that each "leg" of the exhaust has it's own flow impedance curve. This curve is characterized by the function: Pressure Drop = Constant x (Flow Rate)^power. The power is usually between 1.7-2.0. For the loud side, the constant and power is lower than on the quiet side (because there is less restriction), so the flow impedance curves have a similar shape, but the loud side is much more gradual, as pressure drop rises with flow rate. Thus, at high flow, the restriction of the quiet side increases much faster, resulting in continuously lower flow. I stand by my initial analysis.

*fires up ansys multiphysics*

WE SHALL DUEL!

 

[TheDeadCow]

*fires up ansys multiphysics*

WE SHALL DUEL!

Wha? No Fluent CFD?

 

[Zombo]

*fires up ansys multiphysics*

WE SHALL DUEL!

Reminds me of Rocky 3:

"I'm going to bust you up"

"Go for it"

I don't use the "smiles" available, but am looking forward to being corrected, if that comes to fruition...

 

[krt22]

Reminds me of Rocky 3:

"I'm going to bust you up"

"Go for it"

I don't use the "smiles" available, but am looking forward to being corrected, if that comes to fruition...

I was actually for the most part was agreeing with you (but disagree with the pressure relief valve analogy). In this case you have two parallel paths dumping to atmosphere from a higher pressure feed line. The quiet side obviously has more restriction while the loud side is more free flowing, but the total drop over the system is going to remain constant with total flow being the sum of flows going to each leg. At lower flows pressure drop across the quiet leg will be more negligible and the ratio of flows very well could be just as you stated. However once the flows increases and the pressure drop on that leg becomes parasitic, then the regime will change such that the pressure drop across the loud side will start to increase. Once this this happens, the flow through the quiet side will start to level off while while the loud side will increase in a more linear fashion.I agree flow through the quiet side will decrease as a percentage of total flow, but I would not expect it to actually flow less than it would at lower total flow rates. That would mean the pressure drop on the loud side is increasing and thus reduce total overall flow. I would say its a little less tricky than an electrical diagram since the flow is compressible.

If they did not have independent exits to a low pressure area (ie the pipes recombined) then its a different problem. In that case flow through one leg very well could slow or completely stagnate as you stated

Full disclosure: I'm not a fluids guy

 

[JT1]

It's like two resistors in parallel, the side when open will decrease the overall resistance vs both sides closed.

 

[cking]

None of this works till you cut open a muffler and see how it is baffled to begin to estimate flows at different rates.

 

[Donkey]

The GT350 has a valve that either allows sound to come from two of the four exhaust outlets (muffled, quieter) or all four (no muffling, louder). The PCM or another module has programming to open and close the butterflies, based on what the car is doing, I believe. So, if you put the car in Race, I think it opens the butterflies fully, and lets the exhaust sing. In Sport+, the butterflies likely open based on RPM and throttle input, and in Normal mode, the butterflies are likely full closed.

This is similar to what the Roush Active Exhaust does, though the Roush has no connection to the PCM, so it can't read RPM or throttle input, it's just based on user input from the control module/switch.

JR

Why comment false info.. "likely" isn't true at all.

 

[Zombo]

However once the flows increases and the pressure drop on that leg becomes parasitic, then the regime will change such that the pressure drop across the loud side will start to increase. Once this this happens, the flow through the quiet side will start to level off while while the loud side will increase in a more linear fashion.I agree flow through the quiet side will decrease as a percentage of total flow, but I would not expect it to actually flow less than it would at lower total flow rates.

I agree with most of your analysis, except for the part quoted. The curve illustrates what is happening. In reality, the quiet curve is most likely steeper than shown and the loud curve is flatter than shown.

The pressure drop thru each leg is always the same. It's the flow rate per leg that changes to support the equal pressure drop.

The flow thru each leg always increases with increased pressure and never levels out or reduces, but the increase in the quiet side becomes much less at the high pressure condition (high flow).

I think we are all on the same page, and maybe someone in the forum learned something?

 

[torque124]

I agree with most of your analysis, except for the part quoted. The curve illustrates what is happening. In reality, the quiet curve is most likely steeper than shown and the loud curve is flatter than shown.

The pressure drop thru each leg is always the same. It's the flow rate per leg that changes to support the equal pressure drop.

The flow thru each leg always increases with increased pressure and never levels out or reduces, but the increase in the quiet side becomes much less at the high pressure condition (high flow).

I think we are all on the same page, and maybe someone in the forum learned something?

You definitely have a lot of time on your hands :cheers:

 

[lemers]

I agree with most of your analysis, except for the part quoted. The curve illustrates what is happening. In reality, the quiet curve is most likely steeper than shown and the loud curve is flatter than shown.

The pressure drop thru each leg is always the same. It's the flow rate per leg that changes to support the equal pressure drop.

The flow thru each leg always increases with increased pressure and never levels out or reduces, but the increase in the quiet side becomes much less at the high pressure condition (high flow).

I think we are all on the same page, and maybe someone in the forum learned something?

I came up with a new formula to discribe the GT350 exhaust

SM+DS+T=LAE



Where
SM = Sport Mode
DS = Down Shift
T = Throttle
LA = Loud A$$ Exhaust

 

[Zombo]

I came up with a new formula to discribe the GT350 exhaust

SM+DS+T=LAE



Where
SM = Sport Mode
DS = Down Shift
T = Throttle
LA = Loud A$$ Exhaust

You forgot to add the variable RSD: Rear Seats Down!

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