GT4094 and GT4202 cfm flow

[Killerbee]

pulled from garrets site.
80lbmin/.076= 1,056cfm

there you go. And to that you have to apply the result of all your plumbing....and your ACTUAL conditions. That will reduce this number anywhere from 5%-25%, depending on plumbing/CAC flow inefficiencies.

We see this in action with the Induction Overhaul Kit. There is a clear 10%+ increase in MAF...same boost.

I can say for a fact, nobody gets air density over .070 in the summer...just too hot, and few of us live at sea level. IAT typically over 120 F.

I. FOG will change that.

 

[Turbo Buick 6]

Garrett does say 95lb/min at 35psig (50psia).

But what fun is running it at 35?

Yes, we grossly overspeed all these chargers. Garrett's maps are for sustained duty for the planned MTBF (lifespan).

But we like to shorten their lives...

Thank you Pat, I get exactly what your saying

there you go. And to that you have to apply the result of all your plumbing....and your ACTUAL conditions. That will reduce this number anywhere from 5%-25%, depending on plumbing/CAC flow inefficiencies.

We see this in action with the Induction Overhaul Kit. There is a clear 10%+ increase in MAF...same boost.

I can say for a fact, nobody gets air density over .070 in the summer...just too hot, and few of us live at sea level. IAT typically over 120 F.

I. FOG will change that.

This makes sense, but when comparing chargers that is all that should be compared. The efficency of the induction system doesnt matter since not all are the same. Maybe some people can get more out of the same charger but all chargers should be compared with the same standards for it to be fair:baby:

 

[malibu795]

there you go. And to that you have to apply the result of all your plumbing....and your ACTUAL conditions. That will reduce this number anywhere from 5%-25%, depending on plumbing/CAC flow inefficiencies.

We see this in action with the Induction Overhaul Kit. There is a clear 10%+ increase in MAF...same boost.

I can say for a fact, nobody gets air density over .070 in the summer...just too hot, and few of us live at sea level. IAT typically over 120 F.

I. FOG will change that.

Turbochargers are constant volume (vs constant mass) airpumps

that statement is still wrong.

back to the centirfucal pump are vairable displacement. take a 64mm wheel put a 50mm opening in front of it and a 70mm opening in front of it.. the "maf" aka displacement will be less wiht the 50mm vs the 70mm opening.
tho boost most likely will not change.

increase supply pressure or reduce restriction you will increase flow.

bottom line turbo chargers always has been and always will be variable displacement pumps.

 

[Killerbee]

Turbochargers are constant volume (vs constant mass) airpumps

it's not wrong.

the "maf" aka displacement .

MAF and displacement are not synonymous terms. Volume and displacement are synonymous.

As soon as you change IAT, MAF changes, yet the airflow cfm remains nearly constant, for a given constant boost and rpm.

http://members.cox.net/beekiller/GMC%20Light%20Duty/Turbo%20Calc%20spreadsheet.xls

MAF is in cell C27.

Lets disagree and move on.

 

[Fingers]

Turbos are variable displacement. Their output, both mass and volume, varies dependent on the pressure ratio and is not proportional to the shaft speed. Just look at any turbo map.

The only meaningful measure of turbo compressor output is mass/time. That is usually listed as Lb/min, but some times you get grams/sec or some other units. And because the output varies, it is not a simple number but must be presented in graphical form to convey all the factors. Usually listed in the graphs are Pressure Ratio, Lb/min, Shaft speed and efficiency. Bonus are the surge and stall lines.

But what do I know......

 

[Turbo Buick 6]

from what I know a roots blower is a positive/constant displacement pump......correct

 

[malibu795]

from what I know a roots blower is a positive/constant displacement pump......correct

thats what i understand. one of the reason why roote style has instant boost response

centrifical pumps be it SC, turbos, trash pumps are not.


from what i read from KB you put 10ci on the suction of a centrifical pump you get 10ci on the discharger.......

 

[malibu795]

Turbos are variable displacement. Their output, both mass and volume, varies dependent on the pressure ratio and is not proportional to the shaft speed. Just look at any turbo map.

The only meaningful measure of turbo compressor output is mass/time. That is usually listed as Lb/min, but some times you get grams/sec or some other units. And because the output varies, it is not a simple number but must be presented in graphical form to convey all the factors. Usually listed in the graphs are Pressure Ratio, Lb/min, Shaft speed and efficiency. Bonus are the surge and stall lines.

But what do I know......

thanks john.

 

[Turbo Buick 6]

i would think it would varry because the abount of air it moves per revolution chages with different rpms but with a roots it does not.....to an extent, obviously it leaks too much to make boost at 10rpm

 

[malibu795]

i would think it would varry because the abount of air it moves per revolution chages with different rpms but with a roots it does not.....to an extent, obviously it leaks too much to make boost at 10rpm

true they leak.. but not like a centrifical pump.

tevlon strips on the lobes will knock alot of the leak-bye out

one could say only "true" positive would LPAC, MPAC and HPAC. which use piston rings to seal the pumping chambers.

 

[Turbo Buick 6]

true they leak.. but not like a centrifical pump.

tevlon strips on the lobes will knock alot of the leak-bye out

one could say only "true" positive would LPAC, MPAC and HPAC. which use piston rings to seal the pumping chambers.

the point is a rotor or screw type air pump has a displacement rating and that is what it moves per revolution.....regardless of what rpm its turning. now a turbo on the other hand moves more air per shaft revolution the faster you spin it to a point. a centrifical blower proves the point. if it makes 20 psi a 7000 rpm it will only make about 10psi at 3500. this is becasue it moves much more air per blower revolution at high rpm.

 

[malibu795]

boost and LB/min are two different things.

were a roots will prefrom like you described a SC

a centfical SC will prefrom more like a turbo in airflow through the compressor. neither of which have a flow rating for X rpm due to shear nature of the equipment the displacement is variable. and is usually rate at max capacity.

 

[Turbo Buick 6]

i do not know the correct answer for sure, i only say what makes sense to me, but one thing i do know is that a positive displacement pump like a roots is rated at volume per revolution!, yes it varries depending on the boost, but it does not varry with rpm, other than it being too low to seal. a 200ci blower will move 200ci per rev. now at 10psi it may only move 150ci per rev(because it is pushing against something)....but it will move 150ci per rev weather it is at 3000 rpm or 6000 rpm. i belive a centrifical is different. either way i am very curious to get a correct proven answer and will be doing some research tomorrow.....very good thread, not trying to start sh*t, debates often prove good tech:hug:

 

[Fingers]

Positive displacement pumps (piston, screw, lobe,....) Do have a pressure ratio factor when pumping a compressible media like air. It comes from the trapped parcel that is left in the chamber when the pump is done exhausting to the high pressure manifold. That slug re-expands and reduces the amount of gas the next cycle can ingest.

If you look at air compressor specs for instance, you will see that the SCFM rating goes down with increased pressure output. (SCFM rating is the amount of air going into the compressor and not a measure of the volume after compression. Very analogous to lb/min) The smaller the drop, the better the compressor.

 

[Killerbee]

Good discussion!

Mass flow maps are the exception, not the rule. They are typically presented as a convenience to the customer who wants to compare them. They ALL begin life as volumetric axis maps, then a standardized conversion factor is applied to give them an apples-apples usefulness . Hence the MAP is pretty much invalid except for ONE unlikely set of conditions. This is also why they are not a very good absolute reading of actual mass flow rates, until it is corrected for non-standard conditions.

Centrifugal air compressors are not mass devices. They have no idea what the density of the air is.

...and they don't leak, they just have a limit of "push" capability. They are constant head, vs constant volume. But they will spin harder/faster to overcome restriction to satisfy boost set point...they "push" harder. Hence all VGT are subject to overspeed, and there is no safeguard or upper limit except failure (unlike a wastegated turbo)

Restriction is the mortal enemy of the VGT turbo compressor, especially suction side restriction. Few things matter more. I am confusing some, "variable displacement" and "constant head" are different ways of saying the same thing. Sorry. For the compressor, "variable" results from several factors, the most aggregious one is restriction from design plumbing. But then that applies to all centrifugal type "constant head" pumps.