PSI vs. FLOW

[coker6303]

ok, I might be confusing myself so I'm essentially talking out loud.

The example I'm going to use is compounds - stock/475 setup and my 66/80 setup for comparison.

If we are both reading PSI at the y bridge and he reads 50psi while I read 40psi with the 66/80 (these are just numbers for conversation), why would someone say the 66/80 could still be flowing more? If you are taking a reading at the point of work, and PSI is a measure of resistance wouldn't 50psi mean there is more air being forced in?

 

[Ne-max]

CFM is what matters.

 

[malibu795]

ok, I might be confusing myself so I'm essentially talking out loud.

The example I'm going to use is compounds - stock/475 setup and my 66/80 setup for comparison.

If we are both reading PSI at the y bridge and he reads 50psi while I read 40psi with the 66/80 (these are just numbers for conversation), why would someone say the 66/80 could still be flowing more? If you are taking a reading at the point of work, and PSI is a measure of resistance wouldn't 50psi mean there is more air being forced in?

if the said hole is the same on both trucks that a said medium is being shoved through, the higher the PSI the more flow through the said hole. its simple fluid dynamics all things being equal

the thing i would like to know.. whats the air temp as said Y bridge between the two trucks....
hotter air would most likely increase boost and reduce CFM flow

 

[coker6303]

right, I'm all about flow but PSI is showing a resistance to flow.

I guess what I'm asking is how can a turbo setup flow more are to the motor if it is reading less resistance at the intake. By reading at the intake on both, the higher psi would tell me it is seeing more flow at that point right?

 

[coker6303]

if the said hole is the same on both trucks that a said medium is being shoved through, the higher the PSI the more flow through the said hole. its simple fluid dynamics all things being equal

the thing i would like to know.. whats the air temp as said Y bridge between the two trucks....
hotter air would most likely increase boost and reduce CFM flow

I'm sure the stock VGT would net a higher air temp at the intake, so I could see that being a variable where you have less volume of air but higher pressures as the molecules expand.

I'm just confusing myself I guess. I understand fluid dynamics but wanted to ask about this anyway.

 

[malibu795]

I'm sure the stock VGT would net a higher air temp at the intake, so I could see that being a variable where you have less volume of air but higher pressures as the molecules expand.

I'm just confusing myself I guess. I understand fluid dynamics but wanted to ask about this anyway.

i bet there is higher air temp at the inlet of the 60mm VGT than a 66 since the naturally the 475 has a smaller hole to shove through 60mm than a 480 through a 66mm

 

[03spoolindmax]

right, I'm all about flow but PSI is showing a resistance to flow.

I guess what I'm asking is how can a turbo setup flow more are to the motor if it is reading less resistance at the intake. By reading at the intake on both, the higher psi would tell me it is seeing more flow at that point right?

Boost is a means of restriction. The less resistance the more flow and lower temps. Heat creates exspansion which would create more pressure.

 

[MarkBroviak]

Air density is what is being over looked. The air density is the amount of oxygen within the cubic ft of air being moved which is directly related to the temp of the air. The amount of power that can be made is directly controlled by the oxygen content of the air charge.

 

[DieselmafiaLLY]

if this makes sense the way I think of it is stock injectors vs something like 40overs....the stock need much higher pw(or boost in the case of turbos)to achieve the same power as the modded ones with more flow at a lower pw(in your case the lower boost out of bigger twins)

 

[Magnus]

If you understand fluid mechanics and fluid dynamics then think of it in terms of efficiency. At a given power level If the 66/80 are each running in the upper 70% of isentropic efficiency while the stock/75 are pushed into the lower 60% range you end up with air coming out of the 66/80 at much closer to ambient temperature and much higher density and smoother more laminar flow. It's not a volumetric flow rate that matters at all. The two sets of turbos aren't flowing the same volume of air at all, theyre flowing different volumes with both having an equal MASS flow rate to make the same power. That is how a properly sized combo can operate at a higher efficiency resulting in lower pressures and temperatures all around with more total oxygen reaching a cylinder and more power potential at a lower "boost pressure" with all else being equal.

Thermodynamic/fluid mechanical systems are all about understanding mass and energy balances and being aware of what a measured value means. Pressure can be indicative of a resistance to flow, but pressure by itself is meaningless unless you know other variables involved.

Hope I don't come off as a douche, I don't mean to sound like I'm talking down to anyone.