dual charged 3800

[nocutt]

Proportionately, the pressure difference accross the blower remains the same regardless of how much boost you're feeding into it... so its still going to "leak" just as much (well, maybe even worse since the absolute pressure difference is greater)..

Seemingly...based on this then we should invariably see NO net effect...since boost will simply run the other way because we will nearly get into a multiplicative abs. pressure ratio in the inlet...however without the turbo, before the blower is a depression...vacuum. With the turbo, while spooling the depression is now behind the turbo; so the SC sucks air pass the compressor, while in boost the situation is quite different. The turbo supplies the positive displacement SC with more air than it can suck singularly...the engine is the lowest pressure area.
Of course the Sc is a mechanical device it cannot be a complete seal but I would say by any margin that due to a greater pressure differential there should be a reverse...it is a positive displacement pump afterall...

[The Dark Side of Will]

...The SC is mechanically driven off the crankshaft. This means that it always tries to overfeed the engine by the same amount. It doesn't matter if it's being fed by air that's 14.7 psia or 34.7 psia. It will try to increase the pressure of that air by the amount the S/C's volume flow rate exceeds the engine's volume flow rate. You don't make any leakage problems go away by pressurizing the blower inlet because the blower outlet will always be at a higher pressure. This is why twin charging is less efficient than a turbo by itself. No matter how well intercooled the higher density air is, the blower will still add plenty of its own heat and the engine can only take so much boost. 25 psi twin charged will have HUGE intercooling needs compared to 25 psi from a highly efficient turbocharger.

Will based on thermodynamics it matters. Using a flight of staircase as a rudimentary analogy...two ppl, one of each standing at the middle and bottom of the staircase have different potential energy; the bottom been the least equates to a motor starting from atmospheric pressure. The man at the middle is halfway and equates to an engine starting with pressure (higher density) who will make it to the top first? The variable we are concerned with here is air!! now lets look at the temperature...first why is a roots so inefficient? by virtue of their design! Since the roots is nothing but a pump, it only moves air and this air is pressurized in the inlet (after the blower). We understand the process of compression creates heat however this pump also allows air...heated air by the way to "leak pass" the vanes of the blower thereby heating additional air behind the blower...
Now with pressurized air been pumped by the turbocharger into the blower, the blower cannot "regurgitate" heated air thereby the turbo also "seals" this imperfection.
Another quality is a depression is also created infront of the turbo by virtue of the sc...which happens to "jumpstart" the compressor. In other words, there is a synergistic quality to this setup done right...
We both agree going more than 2 bars imho is definitely an intercooling nightmare...at least in the fiero!

It is a very worthy and streetable setup done right...I cannot describe the feeling of such a setup...Boscolingus will and can testify...a v6 fiero not chirp tires but burn them thru the first 3 gears...plenty potential :salute:

"Synergy" doesn't exist when two processes of vastly different efficiencies are trying to accomplish the same goal.

If a 1.5 litre blower is driven at a 2:1 overdrive, it moves 3.0 litres of air per engine revolution. This means that if you put the supercharged engine in a black box and try to guess what it is, you'll think it's a 6.0 litre engine because of the way it pulls air. Was the turbo used on the twin charged project sized for a 6.0 engine?

so if the blower is moving 3.0 litres of volume per engine rev, and the engine's only moving 1.9 litres of volume per engine rev, then the boost, @$$uming 100% adiabatic efficiency, would be a bit less than 9 psi. This means there's a 9 psi pressure difference across the blower with 15 psia (atmospheric ambient) at the blower inlet.

If you put a turbo outside this system, then you'll feed the blower with whatver boost the tubo makes. If the turbo makes 15 psi boost, that's 30 psi absolute. Feeding this pressure into the blower results in 47 psia blower discharge pressure, or about 32 psi boost, again assuming 100% efficiency. The pressure difference across the blower has risen to 17 psi.

Do you think the blower's going to leak more or less at 17 psi than 9 psi? These numbers will only get worse when real efficiency is factored in, since boost will go up at the same mass flow due to temperature increases.

[nocutt]

"Synergy" doesn't exist when two processes of vastly different efficiencies are trying to accomplish the same goal...

Believe me synergy exist with a compound system like this Will, think about it for a second. Disadvantage of both a blower and a turbo are almost removed generally speaking...so both units (which compress air differently) are better than the sum of its parts...Also to add you cannot look at efficiencies on paper to say one or the other is better and therefore will drag the other in this particular context because it appears to me that you are contradicting yourself here; you have already established the efficiency of such a system will be as low as .4X somewhere on the this thread, combining things that produce power in different ways. For the same reason if we where to reverse the staging. If we were to put the turbo as the secondary power adder then we cannot even look at a compressor map, why? it no longer applies.

...If a 1.5 litre blower is driven at a 2:1 overdrive, it moves 3.0 litres of air per engine revolution. This means that if you put the supercharged engine in a black box and try to guess what it is, you'll think it's a 6.0 litre engine because of the way it pulls air. Was the turbo used on the twin charged project sized for a 6.0 engine?...

Good point...but no matter what, the engine is still 3L, mass of air is crux not volume and as such the size of the compressor can afford to be "norminal" in size...the turbine is where the power lies and should be a better focus...remember we have also agreed it was or should be a low to mild boost scenario...as long as the gearing on the SC can create boost on the aforementioned engine, the centrifugal compressor can afford to be negligible...i hope I am making sense?

...so if the blower is moving 3.0 litres of volume per engine rev, and the engine's only moving 1.9 litres of volume per engine rev, then the boost, @$$uming 100% adiabatic efficiency, would be a bit less than 9 psi. This means there's a 9 psi pressure difference across the blower with 15 psia (atmospheric ambient) at the blower inlet. If you put a turbo outside this system, then you'll feed the blower with whatver boost the tubo makes. If the turbo makes 15 psi boost, that's 30 psi absolute. Feeding this pressure into the blower results in 47 psia blower discharge pressure, or about 32 psi boost, again assuming 100% efficiency. The pressure difference across the blower has risen to 17 psi.

Do you think the blower's going to leak more or less at 17 psi than 9 psi? These numbers will only get worse when real efficiency is factored in, since boost will go up at the same mass flow due to temperature increases.

Will in theory, we take a turbocharger, at 7psi (psi=gauge pressure=gp) we are compressing and heating the air up no more than thermodynamically possible. The air now is at a higher density right? A positive displacement SC, has a high volumetric efficiency driven at 8psi (gp) and moderate speed, the blower only moves air; it is the act of back flow (air in the inlet pushing backwards) that compresses the inlet manifold and as long as low boost, moderate speed is maintained leakage is constant at least till equilibrium is reached were it will be either minimal or non-existent...albeit speed is directly proportional to boost in this case...we are talking ambient conditions right?
In our context, the blower is starting from a higher density, the volumetric quality is still the same at this blower speed...however not its mass...that to me is making the blower efficient; side from replacing the blower to a larger unit...agree?
You are right there is a differential between the compressors output (blowers pressurized inlet) with that of the blowers output that should be addressed but contrast the differential when there is no pressure from the turbo versus the other scenario with already pressurized air...the SC is NOT starting from "0" vacuum but from 7psi (gp).
If you are suggesting the leakage is more due to more overall pressure in the inlet, then I will argue that technically a gasoline engine can compress air to about 2XXpsi atmospheric I don't know if "puking" is an issue...

Edit: I re-read your argument...got it!

[EBSB52]

Isn't it fun to watch nerds fight? :blah5:

JK'n, these intelects are the ones who draw up the cool shit and make it work. :thumbleft:

[Kohburn]

For the same reason if we where to reverse the staging. If we were to put the turbo as the secondary power adder then we cannot even look at a compressor map, why? it no longer applies.

thats rediculous, in a dual setup the turbo is chosen to fill in the top end power where the supercharger would otherwise drop off. if you put the charger first then it the turbo will do nothing but add heat because it can't suck more air through the supercharger.

[The Dark Side of Will]

Believe me synergy exist with a compound system like this Will, think about it for a second. Disadvantage of both a blower and a turbo are almost removed generally speaking...so both units (which compress air differently) are better than the sum of its parts...Also to add you cannot look at efficiencies on paper to say one or the other is better and therefore will drag the other in this particular context because it appears to me that you are contradicting yourself here; you have already established the efficiency of such a system will be as low as .4X somewhere on the this thread, combining things that produce power in different ways. For the same reason if we where to reverse the staging. If we were to put the turbo as the secondary power adder then we cannot even look at a compressor map, why? it no longer applies.

Synergy exists when two systems follow different paths to accomplish the same goal in a more efficiently than either could alone. When a blower and SC are used in series, the overall system efficiency suffers. This is NOT synergy. I've laid out why the efficiency drops. If you think there's an error in what I've outlined, tell us what it is.

Good point...but no matter what, the engine is still 3L, mass of air is crux not volume and as such the size of the compressor can afford to be "norminal" in size...the turbine is where the power lies and should be a better focus...remember we have also agreed it was or should be a low to mild boost scenario...as long as the gearing on the SC can create boost on the aforementioned engine, the centrifugal compressor can afford to be negligible...i hope I am making sense?

I know mass is what matters, but constant DISPLACEMENT superchargers don't move mass. They move volume. They move it inefficiently and can add enough heat to the charge to reduce mass flow while increasing volume flow for an incremental increase in speed.

Will in theory, we take a turbocharger, at 7psi (psi=gauge pressure=gp) we are compressing and heating the air up no more than thermodynamically possible. The air now is at a higher density right? A positive displacement SC, has a high volumetric efficiency driven at 8psi (gp) and moderate speed, the blower only moves air; it is the act of back flow (air in the inlet pushing backwards) that compresses the inlet manifold and as long as low boost, moderate speed is maintained leakage is constant at least till equilibrium is reached were it will be either minimal or non-existent...albeit speed is directly proportional to boost in this case...we are talking ambient conditions right?
In our context, the blower is starting from a higher density, the volumetric quality is still the same at this blower speed...however not its mass...that to me is making the blower efficient; side from replacing the blower to a larger unit...agree?
You are right there is a differential between the compressors output (blowers pressurized inlet) with that of the blowers output that should be addressed but contrast the differential when there is no pressure from the turbo versus the other scenario with already pressurized air...the SC is NOT starting from "0" vacuum but from 7psi (gp).
If you are suggesting the leakage is more due to more overall pressure in the inlet, then I will argue that technically a gasoline engine can compress air to about 2XXpsi atmospheric I don't know if "puking" is an issue...

Edit: I re-read your argument...got it!

Yeah, the blower leaks because the pressure difference across it rises as blower inlet pressure goes up.
I didn't say that twin charged systems don't work. I just don't think that conventional series TC systems work well. You can get power out of a flat head Ford if you try hard enough, but it's far from optimal.
VW's method of clutching the blower out of the system essentially makes the turbo & SC parallel systems and DOES allow synergy, but this isn't possible with the turbo blowing through the SC all the time.

I'd also guess that for a given peak power a twin sequential turbo system could give as much boost as a turbo/super combo at any RPM above 2,000.

[p8ntman442]

CVT driven Turbo FTW!!!

always spooled.

forget the inefficiency of a blowoff valve, just increase the diameter of the pulley and create more boost at a much lower volume of flow.

Bloody powerband would be FLAT.




/dream

[Indy]

Variable geometry turbine housing FTOSMFW.

[nocutt]

Synergy exists when two systems follow different paths to accomplish the same goal in a more efficiently than either could alone. When a blower and SC are used in series, the overall system efficiency suffers. This is NOT synergy. I've laid out why the efficiency drops. If you think there's an error in what I've outlined, tell us what it is...

from http://www.thefreedictionary.com/Synergy

syn·er·gy (snr-j)
n. pl. syn·er·gies
1. The interaction of two or more agents or forces so that their combined effect is greater than the sum of their individual effects.
2. Cooperative interaction among groups, especially among the acquired subsidiaries or merged parts of a corporation, that creates an enhanced combined effect. :thumbleft:

Will this may end up been the case of semantics...for all intent and purpose the engine can be looked as a supercharged engine getting turbocharged or a turbocharged engine getting supercharged, but in this context we were referring to an L67 done by WCF, and so it will take the designation of the latter. A stock setup does not heat the air any more than thermodynamics say it should, we are using the same pulley/belt and hence same speed, think of the turbocharger there to compliment the SC because of the SC's own innate issues RPM falloff, back flow compromising fresh intake air etc, etc...with the centrifugal compressor added we have increased the thermal efficiency of the SC...the turbo is ONLY there to provide support to the supercharged engine. We have the stipulation we had already placed about 2 bars...in any event, there is no turbo lag, better throttle response, pronounced top end and a much more broader and flat torque curve...I will say this is synergism, looking at the initial unit we started with first...it has nothing to do with overall efficiency that is purely a thermodynamic issue in which case you will have to know several properties of the system, which you and I know we go beyond the scope of this board...it is like asking what way "an egg will fall if balanced on a pin point in an open system"

...I know mass is what matters, but constant DISPLACEMENT superchargers don't move mass. They move volume. They move it inefficiently and can add enough heat to the charge to reduce mass flow while increasing volume flow for an incremental increase in speed...

Volumetric pumps are inefficient by virtue of their design...but one will be mistaken if suggesting this units are simply inefficient on all counts...not the case as according to Eaton/Mag efficiency can reach up to .9; this is of course very dependent on the dynamic state of engines Ve and speed the unit will be ran at.

Yeah, the blower leaks because the pressure difference across it rises as blower inlet pressure goes up.
I didn't say that twin charged systems don't work. I just don't think that conventional series TC systems work well. You can get power out of a flat head Ford if you try hard enough, but it's far from optimal.
VW's method of clutching the blower out of the system essentially makes the turbo & SC parallel systems and DOES allow synergy, but this isn't possible with the turbo blowing through the SC all the time.

I'd also guess that for a given peak power a twin sequential turbo system could give as much boost as a turbo/super combo at any RPM above 2,000.

I don't know about pressure differential going up Will...that seems to defy some physical principles to me. If anything they stay constant or reduce...in ambient conditions, the leakage equilibrates within the blower. Once this happens I cannot say for sure the amount of internal leakage present...now in a pressurized condition, the differential would solemnly be the difference the blower has contributed to the compressor's pressure...
Honestly to me it depends on who you ask...each individual power adder aforementioned have pros and cons...put together well, I don't see the cons...ppl seldom say "I went turbo because there are more efficient" or "I went SC because there are less efficient"...that is not the argument I know, but it is still a 'think out of the box' mod if you will; which has its place in this small niche...

thats rediculous, in a dual setup the turbo is chosen to fill in the top end power where the supercharger would otherwise drop off. if you put the charger first then it the turbo will do nothing but add heat because it can't suck more air through the supercharger.

Kohburn LOL, you can with a centrifugal supercharger hahaha...I think you took a slice of my point and interpreted it way yonder...the frame of my argument was to simply show if you are using singular efficiencies of the aforementioned power adders as hard values, we can simply flip the stages of this units and efficiency of a unit (here the compressor) is virtually useless...the point? you cannot use efficiency at least not the secondary unit without any wet experiment!!

[Kohburn]

a centrifugal supercharger defeats the purpose of dual charging. they are essentially a belt driven turbo impeller and still take time to spool up. they are more efficient than other superchargers, but it is the worst super to use when considering a dual boost setup because it doesn't gain you any bottom end. you would only be combining the innefficiency of both chargers bo no better boost curve than just using the properly sized turbo to start with.

seriously, look up the boost map of a centrifugal charger and a roots blower.

the only reason to dual charge aside from bling factor is to increase the bottom end torque, a centrifugal won't do this. and the fiero drivetrane doesn't like tons of bottom end torque, thats what breaks things.

[Kohburn]

you cannot use efficiency at least not the secondary unit without any wet experiment!!

um, what?

[Kohburn]

Honestly to me it depends on who you ask...each individual power adder aforementioned have pros and cons...put together well, I don't see the cons...ppl seldom say "I went turbo because there are more efficient" or "I went SC because there are less efficient"...that is not the argument I know, but it is still a 'think out of the box' mod if you will; which has its place in this small niche...

what people have you been talking to? removing superchargers and going turbo to gain efficiency (power) is extremely common, and commonly talked about. people go supercharger because they want more bottom end (if they use logic) or because its cool and whines :la:

people use turbo because its more efficient, provides more power, is easier to install, makes intercooling easier, the boost curve can be controlled completely with an electronic boost controller.

people go dual boost either to make up for a lack of displacement and need both low end and top end, or for bling factor. not because it is the best thing to do.

you can "debate" that untill blue in the face, but thats the facts. do whatever setup you want, i care not. you asked our thoughts on the topic and we shared.

[nocutt]

you cannot use efficiency at least not the secondary unit without any wet experiment!!

um, what?....a centrifugal supercharger defeats the purpose of dual charging. they are essentially a belt driven turbo impeller and still take time to spool up. they are more efficient than other superchargers, but it is the worst super to use when considering a dual boost setup because it doesn't gain you any bottom end. you would only be combining the innefficiency of both chargers bo no better boost curve than just using the properly sized turbo to start with.

seriously, look up the boost map of a centrifugal charger and a roots blower.

the only reason to dual charge aside from bling factor is to increase the bottom end torque, a centrifugal won't do this. and the fiero drivetrane doesn't like tons of bottom end torque, thats what breaks things.

Kohburn without testing the thermal efficiency of the secondary unit how can you say whether or not it is a given value? You can speculate...but that is only an assumption...I think you are taking a small portion of my rhetoric and interpreting it to mean something...it was not an argument, the argument has been made very clear...
In any event, I think "efficiency" is been thrown around to have different facets without an explanation...
BTW you can use two aerodynamic compressors to make a compound setup...it is dependent on what one wants to do. The crux, to compound boost...that is a different matter and not really pertaining to this string

...What people have you been talking to? removing superchargers and going turbo to gain efficiency (power) is extremely common, and commonly talked about. people go supercharger because they want more bottom end (if they use logic) or because its cool and whines la

people use turbo because its more efficient, provides more power, is easier to install, makes intercooling easier, the boost curve can be controlled completely with an electronic boost controller.

people go dual boost either to make up for a lack of displacement and need both low end and top end, or for bling factor. not because it is the best thing to do.

My friend you are preaching to the choir...I really do not want to get into rhetoric here...every potential tuner or DIY has a different argument or reason for going to whatever power adder and can justify their position...the truth is how many do it from an original thought? rather than influence? Again I made a comment in rhetoric :scratch:

...you can "debate" that untill blue in the face, but thats the facts. do whatever setup you want, i care not. you asked our thoughts on the topic and we shared.

LOL... show me where I asked :scratch: for your thoughts on a setup I wanted to build?

[The Dark Side of Will]

from http://www.thefreedictionary.com/Synergy

syn·er·gy (snr-j)
n. pl. syn·er·gies
1. The interaction of two or more agents or forces so that their combined effect is greater than the sum of their individual effects.
2. Cooperative interaction among groups, especially among the acquired subsidiaries or merged parts of a corporation, that creates an enhanced combined effect. :thumbleft:

Will this may end up been the case of semantics...for all intent and purpose the engine can be looked as a supercharged engine getting turbocharged or a turbocharged engine getting supercharged, but in this context we were referring to an L67 done by WCF, and so it will take the designation of the latter. A stock setup does not heat the air any more than thermodynamics say it should, we are using the same pulley/belt and hence same speed, think of the turbocharger there to compliment the SC because of the SC's own innate issues RPM falloff, back flow compromising fresh intake air etc, etc...with the centrifugal compressor added we have increased the thermal efficiency of the SC...the turbo is ONLY there to provide support to the supercharged engine. We have the stipulation we had already placed about 2 bars...in any event, there is no turbo lag, better throttle response, pronounced top end and a much more broader and flat torque curve...I will say this is synergism, looking at the initial unit we started with first...it has nothing to do with overall efficiency that is purely a thermodynamic issue in which case you will have to know several properties of the system, which you and I know we go beyond the scope of this board...it is like asking what way "an egg will fall if balanced on a pin point in an open system"

Because of their use in series and their different efficiencies, using a turbo and a roots does NOT involve any synergy. In order for a combination of two effects to be greater than their sum, the combination must involve a net INCREASE in efficiency. This does not happen.

The blower takes whatever comes into its maw and tries to push that through at a certain volume rate. Because the engine is pulling air at a lower volume rate, boost results, increasing the mass flow at a given volume flow. The blower doesn't care if it's inlet pressure is 4 psi or 40. It'll take more power to drive at 40, but that's because it's compressing a greater mass flow of air (and adding a lot of heat due to its low efficiency). Like all volumetric systems (such as a piston engine), the equations describing blower operation are based on pressure *difference*, while the equations describing the operation of a non-volumetric system like a turbo are based on pressure *ratio*. Trying to apply pressure ratio based ideas to a roots blower doesn't give correct results.

Volumetric pumps are inefficient by virtue of their design...but one will be mistaken if suggesting this units are simply inefficient on all counts...not the case as according to Eaton/Mag efficiency can reach up to .9; this is of course very dependent on the dynamic state of engines Ve and speed the unit will be ran at.

Efficiency of a roots or Eaton might be .9 at next to no boost, but it drops like a stone as boost (pressure difference) goes up.

I don't know about pressure differential going up Will...that seems to defy some physical principles to me. If anything they stay constant or reduce...in ambient conditions, the leakage equilibrates within the blower. Once this happens I cannot say for sure the amount of internal leakage present...now in a pressurized condition, the differential would solemnly be the difference the blower has contributed to the compressor's pressure...

If there's something wrong with my math or my example, find it and explain why. Continuing to disagree without an explanation or acknowledgment/evaluation of the correctness of the example just strikes me as illogical.

Honestly to me it depends on who you ask...each individual power adder aforementioned have pros and cons...put together well, I don't see the cons...ppl seldom say "I went turbo because there are more efficient" or "I went SC because there are less efficient"...that is not the argument I know, but it is still a 'think out of the box' mod if you will; which has its place in this small niche...

People usually go with centrifugal SC's, for instance, because that's what's available or because the kit's cheaper than a turbo kit.

[The Dark Side of Will]

a centrifugal supercharger defeats the purpose of dual charging. they are essentially a belt driven turbo impeller and still take time to spool up. they are more efficient than other superchargers, but it is the worst super to use when considering a dual boost setup because it doesn't gain you any bottom end. you would only be combining the innefficiency of both chargers bo no better boost curve than just using the properly sized turbo to start with.

While I agree that centrifugal superchargers generally are a non-ideal solution, they don't exactly "spool" the way a turbo does... they just don't make boost until the RPM gets high.

[Kohburn]

While I agree that centrifugal superchargers generally are a non-ideal solution, they don't exactly "spool" the way a turbo does... they just don't make boost until the RPM gets high.

didn't say they spooled the same - just that they have to "spool up" - but yes the cut and dry explanation is they don't make boost untill a higher rpm and then have a very linear output after that.

[Kohburn]

LOL... show me where I asked :scratch: for your thoughts on a setup I wanted to build?

ah that was the-dude not you. you are just arguing seemingly for shits and giggles.

[The Dark Side of Will]

While I agree that centrifugal superchargers generally are a non-ideal solution, they don't exactly "spool" the way a turbo does... they just don't make boost until the RPM gets high.

didn't say they spooled the same - just that they have to "spool up" - but yes the cut and dry explanation is they don't make boost untill a higher rpm and then have a very linear output after that.

There is no linear output with centrifugal or axial flow compressors. Airflow is proportional to the square of RPM. That's why turbine engines don't do jack until they're over 85-90% RPM. A centrifugal setup will make peak boost at redline unless there's a boost dump in the system (I'm not sure if some kits use this for a really dumb boost controller or not).

[Kohburn]

just saying the graphs i've seen of the boost output of the centrifugal chargers started boosting around 3000 rpm and didn't hit peak boost untill redline, and the line in the middle was a fairly straight line (ie my statement of linear)

unless i was thinking of the actual power output from using a centrifugal charger, which is entirely possible.

http://www.ststurbo.com/centrifugal

[nocutt]

Because of their use in series and their different efficiencies, using a turbo and a roots does NOT involve any synergy. In order for a combination of two effects to be greater than their sum, the combination must involve a net INCREASE in efficiency. This does not happen....

What efficiencies are you referring too? volumetric or thermal? I just need some clarification?!?...and for the term "synergy" for the sake of not sounding like a broken record...I will respectfully agree to disagree...so we can move forward :thumbleft:
my point was and is simply, twincharging in this context takes the disadvantages of both units applied singularly and removes or minimizes them when combined...

...The blower takes whatever comes into its maw and tries to push that through at a certain volume rate. Because the engine is pulling air at a lower volume rate, boost results, increasing the mass flow at a given volume flow. The blower doesn't care if it's inlet pressure is 4 psi or 40. It'll take more power to drive at 40, but that's because it's compressing a greater mass flow of air (and adding a lot of heat due to its low efficiency)1. Like all volumetric systems (such as a piston engine), the equations describing blower operation are based on pressure *difference*, while the equations describing the operation of a non-volumetric system like a turbo are based on pressure *ratio*. Trying to apply pressure ratio based ideas to a roots blower doesn't give correct results 2...

1 Of course the blower "wants to become an engine" when you are force feeding it...but it still only adds its contribution of pressure to the already higher density air. The mass of air does not matter to the blower...when do you reach a point of diminishing returns I simply don't have numbers to back it up nor do you to say otherwise. Of course conceptually it may seem one way...

This is an example of someone using an M90/turbo on a small displacement engine and is able to get 30Xhp to the wheels @ 9psi. This is ONLY an example regarding numbers...nothing more.
http://www.calaisturbo.com.au/showthread.php?t=90589

2You are absolutely right, no argument there but on an earlier post I tried to differentiate psia from psig...it is too boring to do conversions when I am discussing with someone who can also intellectualize the issue...you know what I meant...

Volumetric pumps are inefficient by virtue of their design...but one will be mistaken if suggesting this units are simply inefficient on all counts...not the case as according to Eaton/Mag efficiency can reach up to .9; this is of course very dependent on the dynamic state of engines Ve and speed the unit will be ran at...

Efficiency of a roots or Eaton might be .9 at next to no boost, but it drops like a stone as boost (pressure difference) goes up.

No argument there either, I actually mistyped that I meant to say .6 ...root blowers have a wider operating range and a higher AVERAGE efficiency...again from the fact that they don't compress air internally, but we are given it a headstart...

...If there's something wrong with my math or my example, find it and explain why. Continuing to disagree without an explanation or acknowledgment/evaluation of the correctness of the example just strikes me as illogical...

Forget the Math, it does not apply and goes beyond the scope of the board...a positive displacement compressor with an isovolumetric process eg a Roots-type blower;
The problem here is the primary stage delivers the air compressed at said pressure, thereby providing said volume. This volume will be the intake of the secondary stage. The secondary stage can match the volume and does not compress the air any more than what is statically does...in any event here is the Characteristic data :

www.eng-tips.com
Q1 = External displaced volume at p1/ time
Qv = internal leakage-losses at dp/time
Qv100 = internal leakage-losses at a dp of 100 millibar/time
q0 = internal displaced volume per rotation
p1 = pressure at inlet
p2 = pressure at outlet
n = number of rotation/minute...
...plus who has hard numbers?

What the formula shows is that each manufacturer and type of blower will have a specific value for internal leakage and not solemnly based on pressure differential...I don't have numbers but it stands to reason given all generations of say the M90as an example their respective internal leakage IS NOT THE SAME, they do all leak but at a certain rate. Again if you are saying the more boost hence more leakage...then you will be right, if we are dealing with ambient conditions; where pulley size dictates the amount of pressure and speed. In this context I have stipulated we go no more than 2 bars. If I do not overdrive the blower and push say 10psig from the turbo...then how does this translate to blower inefficiency...remember we are discussing contextually!!