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Location:
cronulla
Registered:
September 2002
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Re: Mehanical engineers or other informed people - supercharger questions
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Sun, 12 December 2004 13:52
 
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you mean "eaton" style? ie positive displacement?
a positive displacement supercharger DOES NOT compress the air.
it simply moves it from one place to another. when it is released from the confines of the lobes, it encounters air that was already moved there, and THAT is what results in compression with a PD SC.
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I Supported Toymods
Location:
south Melbourne/KL
Registered:
June 2004
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Re: Mehanical engineers or other informed people - supercharger questions
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Sun, 12 December 2004 14:09
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this is what I HEARD from a reliable source.
twin charging (turbo+sc) is not advisable. they say it is better to just go for a bigger turbo (or charger?) to keep things simple n save hassle. results would be pretty much the same n not worth it.
my fren thought of this for his 4agze and quite a number of mechanics told him this.
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Location:
cronulla
Registered:
September 2002
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Re: Mehanical engineers or other informed people - supercharger questions
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Sun, 12 December 2004 14:10
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sorry, yes it is a positive displacement charger.
so if that's the case, this would mean it ceates considerably less heat than a turbo or even centrifugal style charger?
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Location:
Sydney
Registered:
July 2002
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Re: Mehanical engineers or other informed people - supercharger questions
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Mon, 13 December 2004 00:37
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Soon as you compress air it will create heat.
A lot of the twin charger setups is/was a turbo blowing through a positive displacement supercharger. Its a lot less fidly than setting it up to switch over at higher psi.
If you want to get REALLY fancy you could try and find a Lysholm supercharger, they don't produce as much heat, but they are VERY expensive.
Is there room for a small water/air intercooler underneath the supercharger?
I say do it and then work out the results. Ask someone like Capa if it will reduce the life of the supercharger.
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Re: Mehanical engineers or other informed people - supercharger questions
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Mon, 13 December 2004 03:49
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| JAZE wrote on Mon, 13 December 2004 01:10 |
sorry, yes it is a positive displacement charger.
so if that's the case, this would mean it ceates considerably less heat than a turbo or even centrifugal style charger?
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it totally depends on the supercharger... since they are positive displacement, they don't generate heat.. it is the meeting of low pressure air with higher pressure air at the outlet that generates heat.
the straight lobed roots style of the toyota SC's is not good. the very twisted lobe style is better due to a less sudden release of air... the porting of the outlet of an SC can make massive differences to their heat generation.
you would definitely want to cool the air after the SC.. even V8 kiddies are slowely gtting the drift with WTA IC's between SC and manifold..
CYa, Stewart
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Location:
Perth
Registered:
May 2003
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Re: Mehanical engineers or other informed people - supercharger questions
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Mon, 13 December 2004 11:34
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Like everything there is good and bad points for twincharging.
A good example, Lancia S4 Group B rally car 
As Stewart said, the positive displacement supercharger compresses air externally, by forcing more air into a confined space (the intake manifold).
My understanding of it is, in essence the air is being accelerated through the supercharger so that the mass flow of air coming out of the supercharger is greater than than the rate at which the mass flow of air is being consumed by the engine.
In the case where the turbocharger is before the supercharger, once the turbo spools up such that it can maintain or exceed the mass flow rate of the supercharger, there is little need to keep the supercharger operating since the turbocharger is more efficient at compressing the air. The supercharger is only a power drag on the engine (in relation to the overall gain).
With a correctly sized single stage turbo pretty high boost can be reached.
In which case using a roots blower to increase low down torque until the turbo spools up, and then bypassing the supercharger is the way to go (my opinion).
Although an ideal roots blower doesnt add heat to the intake charge, due friction within the supercharger, some heat will be generated.
The other type of positive displacement blower refered to above has the screw type rotors or helix rotors. These are still not as efficient as turbochargers, but an improvement on the straight rotors.
Well there are some of my thoughts on the subject.
EDIT: Clarified some text.
[Updated on: Mon, 13 December 2004 14:11]
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Location:
cronulla
Registered:
September 2002
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Re: Mehanical engineers or other informed people - supercharger questions
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Mon, 13 December 2004 14:31
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The charger, unfortunately is unspecified, its a HKS /ogura unit that can supposedely support up to 1.8 bar. unfortunately the way the kit is set up means it is impossible to intercool without completely remaking the kit, which is currently bolt on.
I was hoping water injection may be sufficient. I was thinking something big up top like a T04 if run through an intercooler would would produce relitavely cool but highly compressed air and feed it to the supercharger, which would not have to work as hard and therefore produce less heat than if it had to suck the air through.
does anyone know if this process would result in the air being re-compressed ie entering the engine at a higher compression than it left the turbo?
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Location:
Perth
Registered:
May 2003
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Re: Mehanical engineers or other informed people - supercharger questions
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Tue, 14 December 2004 11:31
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Originally I wasn't too sure, but the more I thought about, the supercharger should further compress the air.
Ths supercharger moves the air at its inlet to its outlet in a ratio proportional to engine speed. If the air at the inlet is at atmospheric pressure then once moved into the intake by the supercharger it will be compressed to 'x' density.
If the air is already compressed to 'y' density then it would make sense that moving the air at a greater density into the intake manifold would in turn produce an even greater air density in the intake manifold, say 'z' density.
That make sense?
The supercharger displaces a set volume of air per revolution, e.g. an M90 (Eaton) displaces 1.5L per rev at atmospheric pressure. Then if you doubled the pressure (at the intake to the supercharger) but kept the overall volume the same you have approximately doubled the density of air and hence mass of air that you move through the supercharger per rev, i.e. approximately 3L per rev.
It seems logical, but I may be completely wrong.
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Location:
Brisbane
Registered:
May 2002
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Re: Mehanical engineers or other informed people - supercharger questions
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Tue, 14 December 2004 12:05
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You're on the right track. A PD blower moves a fixed volume of air per revolution, regardless of what pressure that volume of air may be at. So if we double the pressure on the inlet side of the blower, it will still move the same volume of air, but twice the mass. And when you think about it, it's the mass of air that makes all the difference once you get to the combustion chambers. 
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Location:
cronulla
Registered:
September 2002
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Re: Mehanical engineers or other informed people - supercharger questions
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Tue, 14 December 2004 12:56
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so im wondering then does this means the charge air after the supercharger will be compressed by what amount, working on logic it should be turbocharger pressure, multiplied by supercharger pressure which is just bonkers, but then again my logic on this sort of thing is no use as, the physics of this are beyond the level i could be bothered to learn.
there seems to be some part of the equation missing, I cant work it out.  I just want to work out what the possibilities are, as im going to do this, but would like to reduce the chance of ruining a turbo, supercharger or engine, ( may end up being a costly experiment  )
I really apreciate all the opinions and facts that people have expressed, it all helps.
cheers
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Re: Mehanical engineers or other informed people - supercharger questions
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Tue, 14 December 2004 13:47
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no no.. the pressure is a secondary thing 
pressure is a measure of air NOT getting into the motor.
if you have a turbo at 15psi, and an SC at 15psi, the same mass of air is getting into motor.
if you blow 15psi air into an SC, it will move that mass of air toward the motor..
hmm, i didn't wanna do calcs but...
say you have motor that consumes... 100L of air with no boost (1bar absolute).. (for arguments sake to make it easy for me ) then if you feed it 15psi air (ie 2 bar absolute), it now consumes 100L, but at double the pressure, so effectively 200L of air at 1atm.
to do this, you need an SC that moves 200L of air (at 1bar) then when it encounters the motor eating 100L at 1bar, to accomdate the extra mass of air, the pressure goes up... (a shit explanation but ya know...)
now you have a turbo feeding 1 bar boost to the SC (2 bar absolute). the SC will move 200L of air at 2 bar absolute toward the motor. ie 400L of air at 1 bar. this is going into motor that can only eat 100L of air, so the pressure will go to 4bar...
hmm, does that sound right?
turbo moves variable volume but constant pressure (at steady state)
SC moves constant volume but variable pressure.
hmm.. i think calc is correct, but it's nearly 1am
Cya, Stewart
EDIT:
this also means that when there is no turbo, you will still have 1 bar boost, but when turbo comes on full, it shoots up to 4 bar...
farrrrrrk...
[Updated on: Tue, 14 December 2004 13:50]
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Location:
Rocky Mountains, Canada
Registered:
May 2002
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Re: Mehanical engineers or other informed people - supercharger questions
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Tue, 14 December 2004 16:54
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Makes me wonder how the 1G-GTZE that Bill had a while ago worked.
Hmmm, maybe i should buy a 1G-GZE instead of a 1G-GTE, and then later, add a turbo to make it twin-charged.
Would make for an interesting project even if it wasnt all that successful (im a DIY/tinkering kinda guy )
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Location:
cronulla
Registered:
September 2002
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Re: Mehanical engineers or other informed people - supercharger questions
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Tue, 14 December 2004 17:02
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So my crappy logic isnt as bad as i thought. Thank you so much for that, although it took a while for me to get it. It seems im going to have to be very careful what boost pressure i run on the chargers. And turbo selection will also be an important factor. IF anyone has any suggestions id be interested to hear them.
If my crappy logic serves, an overly large turbo, on low boost would be the trick?
You dont happen to have any ideas on if the charger will produce more heat if the pressure its creating is higher due to being fed pressurised air by the turbo?
And also do people think a cylinder comp of 8:1 or 8.5:1 would be better?
I know i ask too many questions, but at least this is for a project that is going to happen, as i have begun my buying of all the bits i need. I am very appreciative of everyone who takes time to offer acvice.
cheers.
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