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  #31  
Old 02-17-2008, 10:41 AM
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My question now is why not use a HUGE turbo. Say a GT42 class...
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  #32  
Old 02-17-2008, 11:05 PM
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Ok, I read the title of the thread, and I imediately thought of an issue of Sport Compact Car which I still have! In the June 2005 issue, Dave Coleman covers this quite nicely, and I am going to type out a bit of what he said.

To prelude this a bit, people sometimes think that "oh, the turbo is doing 6 psi and so is the supercharger, so wouldn't it come out at 36 psi?"

Taken from page 26...

"That said, two at the same time can work, but not the way that you might think. First, you must think in absolutel pressure, not boost. Six psi of boost is really 6 psi over ambient. Ambient is usually 14.7 psi, but let's call it 15 psi because we're lazy. Second, you have to look at the pressure ratio across each compressor rather than the simple increase in boost.

In the 6 psi example above, the supercharger takes in air at 15 psi and spits it out at 21 psi, (15 psi ambient plus 6 psi boost) so the pressure ratio is 21/15, or 1.4:1. Now, if you feed that 21 psi (absolute) into a turbo running the same 1.4:1 pressure ratio, you'll get 29.4 psi out the other end (21 psi x 1.4). Subtract ambient (15 psi) and you see that you've got 14.4 psi of boost, not the 36 you were hoping for.

Since you could easily make 14.4 psi of boost with either a supercharger or turbocharger alone, there's little point in using both at this level. Run each compressor a little harder, say at a 2:1 pressure ratio (15 psi, or 1 bar of boost in the real world) and things get more serious. Air comes out of the second compressor at 30 psi (absolute) and out of the second at 60 psi. Subtract 15 psi of ambient, and that's 45 psi of boost. Now, any turbo capable of this kind of boost would be very laggy indeed. so using a supercharger and a turbo in series might make sense. Neither compressor would be working abnormally hard at a 2:1 pressure ratio."



Ok, so hopefully that makes a little sense.

Also, he points out that if you're choosing a turbo for an already supercharged engine..."You need to plan for the mass flow rate of the engine with the supercharger installed, not the engine by itself."

And lastly, I apologize if this has already been gone over. I was on the first page and just hit "reply" and then realized there were two additional pages. So, if someone already said this, or you guys already knew since you're super-smart anyway, then my apologies.
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  #33  
Old 02-18-2008, 02:29 AM
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Thanks Nevin,

You have in affect covered fully, what I suggested only briefly, early on in the thread, i.e. I would expect that you will have to run the SC at much higher RPM than usual, in order that it will boost a high input pressure. It has as it were, to catch up on an already fast moving air stream and push it along some more.
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  #34  
Old 02-18-2008, 07:12 AM
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after doing more research I had found this to be the case already. The s/c is running near its 2:1 pressure ratio now if I pul the 12psi pulley back on. That is it, thats all I can use on this supercharger due to crank pulley size.

The turbo is oversized for the engine alone but should be a great fit of the supercharger as its turbine housing is fairly large with a matching cold side.

The most important thing I need to do first is pick up an engine management system so I can have it on a dyno and tuned for both forms of FI along with my water/meth injection. So thats what I have my eyes peeled for now.

Granted I could just run a gt4088R and have great results but in road racoing, the kind of lag is just not what I want to deal with and the s/c making up for the lag is why I am trying to go this route. Since I already have the s/c it only seems reasonable to add to it rather than re-invent the wheel

Tom
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  #35  
Old 02-18-2008, 07:52 AM
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Quote:
Originally Posted by TomsSVX View Post
BUT what I need to know is if that if the inlet is increased, will the discharge be increased in that same manner?? Or is it more based on volume where sicksubie would be correct

Tom
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Originally Posted by cdigerlando View Post
I think you need an intercooler before you should boost anymore than you already are. I wonder if a twin air water setup could be fabed into your existing supercharger? Then you would not have to do anything more than what your are already doing.
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I know I need some kind of intercooling, aside from LAN's refusal to believe it. I plan on running a front mount for the turbo and a water/meth injection after the blower. the only way to get real control of the injection is to use a standlone tuned for it..
Tom
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Thanks Nevin,

You have in affect covered fully, what I suggested only briefly, early on in the thread, i.e. I would expect that you will have to run the SC at much higher RPM than usual, in order that it will boost a high input pressure. It has as it were, to catch up on an already fast moving air stream and push it along some more.
I think this is a fantastic idea, and I'm very much looking forward to seeing how you get along with it.

As mentioned in a couple of places, including Chuck above, efficient intercooling is the main thing you need to make this work.

Assuming you are not going to raise the hood or create a bump, then you are confined to force feeding the supercharged set-up that you have. This in turn implies you will be feeding turbo driven air to a FMIC then cooled air routed back from the FMIC to feed the supercharger at the throttle bodies.

You will also be adding water, or water/meths, and as Sicksubie says the best method for this is before the s/c. [It not only cools the s/c and rotors, but the vaporised liquid pumping through aids the seal between the lobes]

Regards the pressure vs airflow equation, as Boxersix mentioned, this is where you need to match the two units. You can use as big a turbo as you like to feed the PD blower, provided the max airflow the turbo can pump is not in excess of the max airflow the blower can handle as throughput.

For the record, your 1600AX can handle 702 CFM, so whatever turbo you use feeding this can make as much pressure as you want, so long as it does not exceed what airflow the PD pump can handle.

In respect of that last paragraph, Trevor's point is extremely valid; you will need to gear the rotation of your supercharger to provide the optimum rate of pumping [let's assume max of 702 for the sake of argument, but this is interdependent with how efficient your intercooling will be in the set-up]

So in terms of output, let's assume whatever turbo you intend to use will deliver a conservative 1 atm, say 15 lbs and that in doing this it is pumping less than 702 CFM of air, the max the blower can pump/handle. If unrestricted, this will present 14.7 + 15 to the blower intake, say 30 lbs including atmospheric.

Now assuming your 1600 normally produces a max pressure of around 12 lbs over atmospheric [I have not checked this, just using your max here ], this 12 lbs is a ratio increase of approx 1.8 over atmospheric. So in theory the PD blower will take the intercooled charge from the turbo of 30 lbs absolute and boost this pressure to 54 psi including atmospheric. As you can see this is equivalent to 39.3 or roughly 39 lbs boost over atmospheric.

Pretty damn healthy if it all could be achieved

I imagine it will all get pretty hot at those levels of boost. For reliability you will probably need to gear back the PD blower to the equivalent of 9 or 10 lbs for safety, and you will feed it with a medium sized turbo giving fast response but not exceeding the CFM airflow speed the blower is able to handle at that setting. You will still get mammoth hp and torque provided you can cool the charge enough.

Brilliant, just brilliant.

I let Speedy Gonzalez have the last words.

Andale! Andale!

Joe
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  #36  
Old 02-18-2008, 08:17 AM
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Originally Posted by svxistentialist View Post
I imagine it will all get pretty hot at those levels of boost. For reliability you will probably need to gear back the PD blower to the equivalent of 9 or 10 lbs for safety, and you will feed it with a medium sized turbo giving fast response but not exceeding the CFM airflow speed the blower is able to handle at that setting. You will still get mammoth hp and torque provided you can cool the charge enough.


Joe
Exactly. You must gear DOWN the blower, otherwise you can exceed the max flow rate of the rotors. Unlike the standard Eaton roots style blowers, the Lysholms run a VERY tight tolerance between the male and female rotors which results in very good efficiency but have little area to flow beyond their max capabilities. You will NOT want to run that SC at increased RPMs. 1600ax at 14k rpm is pumping out charge air in excess of 245F. Even with charge cooling that's HOT.

You have little to worry about spraying before the SC affecting the bearings. Lysholms have fully sealed bearings on the rotor side. Stay away from spraying any concentration of meth above a 40% ratio as it can affect the housings, and the MAG rotor if you have that option in your particular 1600. Water/alky works well anyway.
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  #37  
Old 02-18-2008, 08:24 AM
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now this is the next discussion. I planned on cooling post blower out of fear that the density of the water would damage the rotors due to their tight clearances. A pre-s/c water injection would be ideal but I did not want to blow up the s/c either

Tom
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  #38  
Old 02-18-2008, 08:37 AM
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Tom, I think what Boxersix says above is correct, and probably informed by experience as well.

You could choose to spray before the blower, after the blower, or split it using more nozzles.

We have had these discussions with Autorotor, they have built a special blower unit for us. They recommend before the blower as an aid to sealing. I can't see how you could blow it up if all other parameters are thought out properly.

It should work.

Joe
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  #39  
Old 02-18-2008, 08:41 AM
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Ok here are the maps I am working with. Doing the math in a perfect world I would expect 39psi using a pressure ratio of 2.5 on the turbo and the 1.8 I see now on the supercharger. Now granted there will be pressure lost in the real world this is just a round about. Maps for both compressors are below. The lysholm graph is a PDF attached at the bottom



Tom

Last edited by TomsSVX; 07-18-2008 at 01:03 PM.
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  #40  
Old 02-18-2008, 08:56 AM
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A pre-s/c water injection would be ideal but I did not want to blow up the s/c either

Tom
Although that is one thing you haven't blown up yet ...

Is there going to be enough room for plumbing both the turbo and SC equipment?
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  #41  
Old 02-18-2008, 09:05 AM
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Both of those maps are referenced to ambient in relation to pressure increase and temp increase.

With the 1600AX being second in your daisy chain, it will be taking in hot compressed air, compressing it more and heating it more.

It will all still work, just everything will be too hot for effective cylinder temps.

For it to be manageable, from a fuel/air ratio and detonation standpoint, you will need to run the turbo and estimate what temperature air it will supply to the blower.

Then you will need to take that new hotter charge and see how much more temperature the blower will add to what is now being pumped into the cylinder. At this point you will be relying on the water mix injection to keep it below detonation temperatures.

Joe
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  #42  
Old 02-18-2008, 09:12 AM
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fully understood Joe, thats why I mention a perfect world scenario. I am still on the fence of before or after s/c injection.

tom
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  #43  
Old 02-18-2008, 09:13 AM
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now this is the next discussion. I planned on cooling post blower out of fear that the density of the water would damage the rotors due to their tight clearances. A pre-s/c water injection would be ideal but I did not want to blow up the s/c either

Tom
As long as the mist is fine enough and we keep flow limits around say about 450cc/min you won't have a problem. This is in the event that you're using the injection ONLY as a cooling aid and not a method for detonation control. I'm more prone to have the charge cooled post compressor in any event, as the water/alky(meth) mix in the combustion chambers is what really makes the big difference in controlling detonation. I'm sure you're aware that for meth to make it's own good as a tuning aspect it needs to be metered quite precisely just like fuel otherwise A) too little does next to nothing or B) too much and it quenches the flame front in the combustion chamber and kills torque.
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  #44  
Old 02-18-2008, 09:14 AM
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fully understood Joe, thats why I mention a perfect world scenario. I am still on the fence of before or after s/c injection.

tom
your answer lies in what you mainly intend the injection TO do......cool the charge or control detonation. It obviously can and does do both but where you plumb it and how you tune the injection will determine the end result.....
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  #45  
Old 02-18-2008, 09:20 AM
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yeah, I would much rather have heafty det. control over cooling the charge, as det. is what I am fighting with the S/C as it sits now... Just need that Hydra to get started here

Tom
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