Wow, lol, I miss one day and everything goes nuts... Ok here we go:
No.
If there is flow, the pressure MUST drop along the direction of flow.
In a static system, the pressure would be the same everywhere.
This is only true in the piping... not in the vacuum lines controlling the WG and the BPV. The vaccuum lines are connected to the intake mani and pressure drop along the length of the vac lines is minimal enough to say that all three locations retain the same readings of pressure (again inside the vac lines).
icespeed: are you saying that more mass is created when air passes through the intercooler? because no. the density goes up, the pressure goes down to compensate, and the mass stays the same.
I am not saying that mass is created. The mass flow rate (dm/dt) increases. So more mass is travelling in any given time frame. As far as the density and pressure relation is concerned, the ideal gas law is only valid in non-compressible situations. It turns out that if the density goes up, the temperature must go down for the pressure to remain the same. This scenario is not true in compressible flow. It is "almost" true that the mass stays the same, however, once again the rate of mass flow changes. Because it is compressible flow, you can "potentially" have an increase in pressure and an increase in density while lowering the temperature (such as through an intercooler). I must also point out that density and pressure are directly proportional. Your statement is only correct under the following circumstance: if the density goes up, the temparture must go waaayyyy down to cause the pressure to go down.
Yep exactly.
icespeed, The pressure is NOT the same everywhere in a dynamic system (aka flowing). There is a pressure gradient from the turbo to the manifold with the biggest drop in pressure occuring at the intercooler due to the decrease in temperature. This has been measured many times by tuners and manufacturers by placing pressure transducers before and after the intercooler.
This is only true in the piping (as you stated in regards to the turbo-intercooler system) but not in the vaccuum lines.
As far as the pressure, itself is concerned, yes it's true that the pressure is different at different locations in a dynamic system, however as dx -> 0 and da -> 0 (cross sectional area), the pressure of any given fluid is uniform, even in a dyamic system. This particular definition of "pressure" is that of an intrinsic characteristic of said fluid where each particle is exerting an outward force per area against all others as dv -> 0
here is the math: as stated in my above post, it becomes very complex with compressible flow:
dm/dt = (rho, p)(velocity, V)(Cross sectional area, A)
Note: This is the mass flow rate eqution. It says that a change in mass per unit time is equal to the density times the velocity times the cross sectional area [of the piping in this example]. In a non-compressible flow application, it is very easy to determine velocity, m-dot or the cross sectional area. However in a compressible flow application, it is much harder to do.
(Pressure, P) = [(rho, p)(gas constant, R)(Temp, T)]/(Mol mass, M) -
Note: This is the ideal gas law. It is under the assumption that dp/dt = 0 Meaning that this equation is only valid in non-compressible flow. Once Compressible flow is involved, it becomes a very tricky system. It becomes a P.D.E. where we have dP/dt = [ (dp/dt) (R) (dT/dt)] / dM. It cannot just be integrated w/ respect to time, because any one of the d( )/dt's can retain a different order of consistency, thereby allowing energy to be lost from the system.
This leads to even more complex situational considerations. We have neglected viscosity (as it is very minimal in an air situation) and we have also neglected heat transfer. In all reality, this system is not closed and therefore the conservation of energy law is also void. Because heat can be transferred outside of the system, I can say, "It is almost true that mass stays the same..." from the above response.
So, as I stated originally:
It makes sense to me that if all the MS3's were reading from the wastegate, then they all would be off by, give or take, the same amount.
Because a turbo produces compressible flow, the "ideal" gas law goes out the window. It turns out that those are some pretty difficult equations to tackle to give you a 100% result.
However I can say this with certainty. The Pressure drop due to cooling actually increases the amount of charged air entering the combustion chamber. It is all about how much "mass" of air enters. By the temperature cooling and the density increasing, more mass is being moved in any given time frame. It turns out that the rate of mass moving is based on density, velocity and the cross-sectional area of the pipe that it is in. Also remember that pressure in a fluid is the same regardless of where you check the reading in said fluid. So, if the reading is coming from the WG and the WG is connected to the BPV (like the MSP is) which is then connected to the intake mani (again like the MSP is), then the pressure in all three vaccuum lines(WG, BPV, intake mani) is exactly the same.
edit: In short, cooling after the turbo with a pressure drop is more effiicient than no pressure drop and no cooling. Odds are that the WG vac line is connected to the intake manifold, therefore the pressure in/at the WG is identical to the pressure in the intake manifold. Raising the boost to equal out the pressure after cooling = zoom zoom-er... and possibly zoom boom.
Ok, I just re-read my original post. I see where everyone is mis-understanding me. It was the statement, "Also remember that pressure in a fluid is the same regardless of where you check the reading in said fluid." I explained it above, but will do so again. This was in regards to dx and da -> 0 and under the assumption that air is not flowing through the vaccuum lines until the breaching point of the WGA spring, thereby creating a "local" static system, where the WGA, BPV and Intake Mani all have the same pressure. So, Abaddon and Jays07MS3, you are both correct in your statements, but not in regards to the intial values I assumed.
