possible to swap between AFM's on the run?

[mic*]

turbo is much better for sruise conditions than SC, of this there is no doubt.. but SC would not be used for a car where you did not intend to drive it hard

Indeed.

I have scrutinsed your post. The pages do support what you say despite that i worked out 10 psi as closer to 1.7pressure ratio. And 540CFM as 15m^3/min

I am sure you will testify to the fact that comparing specs from different manufacturers creates bias one way or another. Even if its just the different methods and labs used.

Apart from that - design? Actual size difference despite being close?

Logically stu, if all else is constant, a device that has more opposing force (namely internal compression of air, and frictional loss of closer mating lobes) must have a higher power cost to run, yeah???

About the other 13 psi bit i agree too. Nearly every bit of air coming out of a roots design will pass the exit 3 times the way i see it...

[mic*]

Meaning:
-(once - out) air volume X goes out S/C and port closes as lobe moves.
-(twice - in) port opens to pump more air OUT of it, but as it does, coz the air is only atmo, part of volume X pushes back into the S/C.
-(thrice - out) lobe moves further closing port again and volume X along with some new volume is now trapped in the inlet / plenum.

[oldcorollas]

simple fact is, if you compress the air gradually, internally, and then release into manifold, you have a much more efficient method of compressing than just releasing lower pressure air into higher pressure manifold.
if you were to run a lysholm at it's internal compression ratio, there is NO compression in the manifold at all.

closer lobes may have slightly more friction, but the sealing material is air. the lobes never touch. same for eaton and roots. lobes never touch. if they do, the heat generated would fark them instantly (from galling and the like). the heat generated in the lysholm is from compression, the power loss is from the compressed air trying to "unscrew" the rotors.
for an eaton, this is also true, to a point, but since the air coming out is lower pressure, the higher pressure of manifold is also tryign to unscrew rotors....

think of it this way... an roots/eaton is like a normal straight cut/helical cut gear. to push a force, power is more or less acting parallel to the direction of rotation.
for a screw charger, it is more like a worm gear, and then needs to spin faster, but the force acting against it is not quite as parallel to the direction of rotation (since it will act normal to the lobe surface)... perhaps this analogy is flawed, but the data doesn't lie. screwchargers take leess effort to spin them to create same manifold pressure for same flow.

the down side is the heat generated at all times, so you don't get something for nothing.. but as corky bell said, even for a constantly running screwcharger, you only need to increase IC size by 10% to remove the heat generated during cruise conditions (since the expanding air in the manifold... at lower pressure than the SC exit.. will actually ABSORB heat as it expands)

anyways., it's an interesting subject of course.. btu the easiest way to do twincharging is how lambolica pictured it, and that came out from the discussion on last forum... it's hard to beat having turbo blowing into SC, and then perhaps turning SC off at higher rpm (doesn't matter if it is on or off is both sides of the SC are at same pressure )

[mic*]

Yeah your analogy isnt that bad and data doesnt lie this is true, but obviously a lot of theory from a number of sources could be dispelled by that data.

I know air is the "sealant" - purely by resistance through the tiniest of clearances but you know what i meant when i said more frictional loss.

Interesting topic indeed.

it's hard to beat having turbo blowing into SC, and then perhaps turning SC off at higher rpm (doesn't matter if it is on or off is both sides of the SC are at same pressure )

What makes you think that if its ON that both sides are same pressure? As long as the turbo can support the flow the S/C MUST positively displace air. Try and make sense of my earlier post...

Would just be like sizing a turbo for a much larger displacement engine than what you are actually using it for...

[oldcorollas]

What makes you think that if its ON that both sides are same pressure? As long as the turbo can support the flow the S/C MUST positively displace air. Try and make sense of my earlier post...

Would just be like sizing a turbo for a much larger displacement engine than what you are actually using it for...

if you have a turbo, blowing into an SC AND a bypass around the SC, then the SC is displacing air, but if both sides of the SC, and the bypass, are all at the same pressure, all the SC is doing is rerouting air from the bypass, and consuming some power to do so (but not that much.. not compared to when it is compressing).. so if it is on or off, makes little difference.. both to flow (bypass can flow it anyway) or power (it's not drawing so much either)...

yes, turbo would be larger.. i still maintain that twincharging would be great of you wanted to run from sayy.. above 25-30psi on a street motor, but apart form that....

[mic*]

if you have a turbo, blowing into an SC AND a bypass around the SC, then the SC is displacing air, but if both sides of the SC, and the bypass, are all at the same pressure, all the SC is doing is rerouting air from the bypass, and consuming some power to do so (but not that much.. not compared to when it is compressing).. so if it is on or off, makes little difference.. both to flow (bypass can flow it anyway) or power (it's not drawing so much either)...

yes, turbo would be larger.. i still maintain that twincharging would be great of you wanted to run from sayy.. above 25-30psi on a street motor, but apart form that....

Sorry. The picture in my head did not have a bypass - you were referencing Lambolica's diagram.

I just wouldn have the bypass. Whats it there for except to limit power? I see no beneficial reason to adding that extra plumbing and rooting around involved therewith.


I totally agree that twin-charging is about big boost thats not all right up top end...

[oldcorollas]

Sorry. The picture in my head did not have a bypass - you were referencing Lambolica's diagram.

I just wouldn have the bypass. Whats it there for except to limit power? I see no beneficial reason to adding that extra plumbing and rooting around involved therewith.

no worries, you do it your way

i'll do it mine


reason is so you can switch off SC.. SC running at sayy 14psi from idel to 5000rpm, will nto be happy going to 9000 or so rpm. (roots crappy SC i mean)

you wanna spin it 1.5x it's max rpm just for the heck of it? whilst running hot turbo compressed air thru it? seee how long the rotors last i suppose...

[brett_celicacoupe]

i was looking into this very carefully not long ago.
it was my planned next upgrade (either that or a 1jz-gte ) im still deciding which way i go

anyway... my plan was to bolt on the SC14 onto the 1ggte block and having the SC feed the CT12's. this would be just a pipe running under the engine and going up to the turbo T piece inlet from the SC output. then, the AFM would be moved to the other side of the engine bay and plumbed to a Y piece, one pipe to the SC inlet, one to the bypass valve.
[advantages; SC runs through intercooler, minimal piping, can keep factory AFM]

the next part involves a 1jz-gte (wilbo666's idea) traction control throttle body running parralel with the SC, acting as a bypass. youd cut the cable TB off ofcourse
[advantages; controlled electronically, decent size]


here is the diagram i made , as to how i would be running my setup:


so now the plumbing is all sorted....its down to the hard bit; controlling when the SC is on.

seeing as the bypass valve is electronically controlled rather then wastegate/actuator style, it can be controlled by a microcontroller. this would also tell the SC when to turn on or off.
[advantages; programmable, can be programmed for smooth transition between SC/turbo]

a couple sensors would also be needed to moniter pressure
1) between SC and turbo's
2) post turbo's

these are the basic commands that would dictate how the SC and bypass valve would operate.

SC engaged;
1)engine RPM >1100rpm (so its not on whilst idleing)

SC disengaged
1)engine RPM >3500rpm
2)boost after turbo's exceed maximum boost output of SC
3)pressure in the pipe between the SC and the turbo's drops below ~1psi ( assuming pressure between SC and turbo's will drop when turbo's begin to displace more air than SC????)
4) manifold vacum is more then ~20inHg (so the SC disengages whilst cruising along )
5) override switch
note: SC takes 2 seconds to disengage under all circumstances except when pressure between SC and turbos falls to ~2psi while SC is engaged. (to stop SC cutting in and out between gear changes)

bypass valve closed:
1) when SC is engaged

bypass valve open:
2) SC is disengaged

now that stuff above is all theoretical conditions and what i thought of off the top of my head so im not 100% sure if it will work as desired. but seeing as a microcontroller controls everything, it can modified and more sensors can be put in if needed etc.

anyway - what do ppl think?

[RAd28]

Brett: the operation of your set up, covers basically the same as what i had planned... although i planned using a independent supercharger setup... basically like a TE and ZE hybrid... the problem i see with my idea is you'd need a twin throttle body style valve (or something similar, to control which compresser (turbo, or SC) blows through to the plenum... since if your running 2 AFM's (as in my suggestion) you couldn't have a combined reading... hmmm now i think about it... flawed in more then one way..

[Lambolica]

Nice..... pretty much the concept I had However electronically controlled. In my opinion the the bypass valve would be in the s/c plumbing but that was somthing Stu and I came up with ages ago.

you have thwe advantage of swithcing the s/c at differeing points and the list of senarios is pretty complete so you should be able to tweak any issues.

In you case brett I'm pretty sure it would be easy to adapt a pressure sensor to act as a switch to a basic controller to do the desired I/O's

My concept (or stu and my) was to use a throttle or waste gate actuated buy pressures. in my concept the turbo is before the S/C and the thottle is opened when the air pressure is equal either side if the throttle, when the turbos overtake the S/C on which the throttle (using the TPS switch) disengages the S/C. meaning there should be smooth transioton between the 2. I am 99% sure there is a flaw here somewhere.

[brett_celicacoupe]

it would be so much damn easyer if the engine was MAP sensored....but ohh well

[oldcorollas]

it would be so much damn easier if the engine was Megasquirted....but ohh well

fuxed

[RAd28]

amen to that...

Lambo: anything simple usually is flawed... such a bastard that

[brett_celicacoupe]

haha - but if i went to megasquirt or similar then id just get a big ball bearing turbo and run >20psi. but theres a couple grand alone in those things.
i would expect to convert to 1g-gzte for around $600

[mic*]

Nice..... pretty much the concept I had However electronically controlled. In my opinion the the bypass valve would be in the s/c plumbing but that was somthing Stu and I came up with ages ago.

you have thwe advantage of swithcing the s/c at differeing points and the list of senarios is pretty complete so you should be able to tweak any issues.

In you case brett I'm pretty sure it would be easy to adapt a pressure sensor to act as a switch to a basic controller to do the desired I/O's

My concept (or stu and my) was to use a throttle or waste gate actuated buy pressures. in my concept the turbo is before the S/C and the thottle is opened when the air pressure is equal either side if the throttle, when the turbos overtake the S/C on which the throttle (using the TPS switch) disengages the S/C. meaning there should be smooth transioton between the 2. I am 99% sure there is a flaw here somewhere.

Yeah i am about 99% sure there is a flaw too... Thats what ive been trying to put into words.

If the S/C is after the turbo, as soon as the turbo starts making any boost, the S/C will be DOUBLE BOOSTING - even if its only 1 psi between Turbo & S/C... And the air demand goes way down as soon as the bypass opens & SC is off. So turbo spinning at X rpm's is displacing Y flow @ <1 psi, switch is tripped to turn the S/C off, then it must continue at X rpm's, Y flow and 10psi (hypothetical 1.7pressure ratio of S/C disappearing)? Its not gonna happen. Its like closing a throttle body on the turbo...

And if you leave the switch on until the turbo makes even 2psi boost between it and the S/C;

2psi boost = 16.7 absolute

16.7 X 1.7pressure ratio = 28.39psi absolute

= 13.7psi boost...

I have it... The flaw is simple. The turbo will never overtake the S/C coz the S/C will boost whatever is thrown at it. The bypass MUST be opened before any pressure above atmo exists between the T & SC so you dont feel the DOUBLE BOOST disappear, and even then im sure you will feel a drop off while the turbo gets up and going...


Brett, what you have suggested there sounds fantastic. If i wanted to twin charge and use them independently (which i still say goes against the principle of it) that is how i would do it... Well thought out