Sunday, January 27, 2008 - 03:22 pm, by: Jeff Bedsor(Jeff_bedsor)
I have been running 18-20 psi through mine for 6 months, so I would call that safe. With everything standard you are only going to be able to run about 13 psi before you hit boost cut, if you can get something to eliminate the cut 16 should be fine.
Sunday, January 27, 2008 - 08:35 pm, by: Brad Knudsen(Knuddo)
Boost pressure is the amount of pressure created by the turbo(s) usually measured at the intake manifold. It does not matter how many turbos you might have wether there be 1, 2 or more. If you were to measure the pressure coming out of your one of your turbo compressors (i.e. the front turbo), then that compressor will show roughly the same amount of boost pressure as you would have going into you intake manifold (not taking into account pressure drop between turbos and intake). It is not a matter of dividing or multiplying. The simple answer to your question is - if you are making 18psi, then each turbo is making 18psi. Cheers Brad
Sunday, January 27, 2008 - 09:13 pm, by: Luke Burt(Burt)
Uh.. Brad, if you are making 18psi, all things being perfect, then the turbos will be making 9psi each..
What your saying makes no sense at all. What aska is asking also doesn't make sense, you can't measure what each turbo is running, as both outlets from the turbo's on the standard 1J piping share a common pipe, the pipe is pressurized, meaning a readin from either turbo outlet will be the same. The only way to measure what each turbo is actually running on a twin setup, is to have twin throttle bodies, with a turbo plumbed seperately into each TB.
Please correct me if i'm wrong..
Brian Timms DieHard New South Wales TT Soarer Goodness.
Sunday, January 27, 2008 - 09:25 pm, by: Brian Timms(Turbo_brian)
To measure the turbochargers, you either need a 1 way valve (doesn't exist) or twin throttle bodies to seperate the pressures from each turbocharger.
Both turbochargers blades are subject to 18psi of pressure, but are making this pressure combined.
There is a rule of thumb, while there is an air path in a sealed atmosphere (the atmosphere being the air between the turbochargers and intake manfold) the pressure will evenly spread and equalise throughout the atmosphere.
Therefore technically, the measurement from Turbo a's outlet and Turbo B's outlet should equal the pressure at the intake manifold, which should equal the pressure at the intercooler.
Now in reality this is not always the case, as long as the turbochargers are producint positive pressure, you can technically read the turbo's pressure, but only while on boost.
With intercooling, this creates a chamber that alter's the atmospheric pressures and temperatures, changing the environment from the turbocharger to the intake manifold, which changes pressures as well, so there are so many factors that can effect what is being seen.
Most people will know if a turbo has gone in their twin turbo setup (other than noises) because they tend to loose power in the top end, and boost seems to bleed away in the non-boosting turbocharger.
B.
Steven Nanevski Goo Roo New South Wales D Day has almost arrived....
Monday, January 28, 2008 - 12:09 am, by: Steven Nanevski(Imprestik)
Luke Burt wrote on Sunday, January 27, 2008 - 09:13 pm:
Uh.. Brad, if you are making 18psi, all things being perfect, then the turbos will be making 9psi each..
You are completely wrong there, I wish that was the case....
If you are running 9psi of boost, you are running 9psi of boost from both turbos, which means 9psi from front + 9psi from rear = 9psi out of both turbos.
If it was your theory mate, everyone would keep the twins, run 15 to 18psi out of each turbo which would = 30 to 36psi and have 500+ horses at the rears. Would make modifying a little cheaper too
Monday, January 28, 2008 - 07:31 am, by: Brad Knudsen(Knuddo)
With a twin turbo setup, because both compressors are connected to the same pipe work, the air pressure will be relatively even. Remember - pressurised air will always move to a low pressure area. If you were to blow into a balloon - the presser will be the same no matter where it is measured in that balloon.
The thing to remember is that it’s not all about boost pressure. Boost pressure is relative to air flow. Think of having two garden hoses with deferent Internal Diameters. The larger hose will move more water at the same pressure than the small hose. The Compressor on a turbo is designed to pump a certain amount of air (mass flow rate) not necessarily at specific pressure levels. Boost pressure is relative.
If you were have the same turbo on a 2ltr engine as a 3ltr engine and moved the same amount of air – the boost level of smaller engine would be much greater. This is of course not taking into account engine head design, turbine housing or engine rpm. On the other hand if you had a twin turbo setup and one of those turbos failed, your air flow rate will drop dramatically and hence your boost pressure will also drop due to A. Less resistance for that amount of air going into the engine & B. Possible loss of air flow through the failed turbo compressor.
In other words, don’t get carried away with boost pressure levels as it’s all relative. If it was all about boost pressure than correct turbo selection wouldn’t be so important.
I hope I haven’t overly complicated things here. Cheers Brad
Monday, January 28, 2008 - 10:12 am, by: Luke Burt(Burt)
Thanks for the correcting, but now i need to understand what you're saying. So if both the standard CT12A's are running say 13psi each, and your only getting 13psi to your manifold, Couldn't you (if you had twin throttle bodies) plumb them both seperately and run 13 at each, making 26psi?
I'm not in any way saying you guys are wrong i'm just asking for a explanation so i can understand it
As they are on a bi-setup i know they are basically acting as one turbo, as they share common piping, so no matter where you measure the boost it will be the same.. so, lets say that the turbines need to be spinning at 90,000rpm to make 10psi in the twin setup. So a CT12A on a single setup would also only need 90,000rpm to make 10psi is my understanding from what you guys are saying. Maybe it's just the way you have worded it, but i could say that ok there are some people running 16psi on the standard turbo's, if that means each turbo is pushing out 16psi, then you could (with twin throttle bodies) run 16psi from each turbo equalling 32psi, but i know that isn't the case.
I know on the bi-setup whatever you are boosting is what is happening from the turbo's, but the load has to be shared, and if i were to run a CT12A as a single turbo its max would be what.. 7-8psi?
So if all things perfect on a bi-turbo setup, would each turbo not contribute equal boost pressure, having equal load?
Monday, January 28, 2008 - 02:20 pm, by: Peter Nitschke(Pen)
Whether you split the throttle bodies or not, doesn't make any difference. At the end of the day, you are still feeding 6 cylinders with boost, no matter how the plumbing is designed.
Feeding 1 turbo to 3 cylinders or 2 turbo's to 6 cylinders, still no overall difference in the pressure required or achieved. Even 6 small turbo's feeding 1 cylinder each would all need to make 13 psi each, if that is the boost you wanted for the engine. Just that they wouldn't each need to pressurise such a big volume of air as they would only be feeding one cylinder.
The turbo's are in parallel with each other, if they were in series, then perhaps your first assumption of 9+9=18 might make sense.
So the reason for 2 turbo's is that 2 smaller turbo's can pressurise a large enough volume of air for the 6 cylinders while still being small enough to have fast spool times.
When people go to a single turbo, they invariably get more lag as the bigger turbines don't spin up as easily.
Tuesday, January 29, 2008 - 12:21 am, by: Aska Liu(Icarus1314)
woh~ guys thanks for the reply!!
this soarer is actually the first turbo charged car i have ever driven, and untill now i dont really understand how turbo works~ i dont know who if wrong and who is right up there, but i think now i have a better understanding thanks to you guys~
i have did a bit of research myself as well, about how turbos work ect ect~ but still no sure how twin turbo works , all i know is it reduce the turbo lag...
anyway thanks again for the replys guys, and hmmmm just wanna make sure before i blow up my engine, if i boost the turbo to about say 15psi, it shouldnt be too much of a damage to the engine right? (concidering everything is stock)
p.s: i have lately come to notice that my car has a really slow take off, i have made a post in the "Z10/Z20" area with more detial, if any of u have spare time plz take a look at it and see if u can help me~ thank you ~
Tuesday, January 29, 2008 - 01:17 pm, by: Luke Burt(Burt)
Aska, what the other guys have said is pretty much correct. I just didn't explain what i was trying to say very well, and have been mis-understood. I shouldn't have mentioned boost as factor between the turbo's sharing the load. More or less what i was trying to say, if you seperate the turbo's, keep total volume of the area to be pressurized the same, they should be able to produce half the boost of the bi setup at the same RPM. Meaning when working together they can make say 16 psi at 90,000rpm each.
If you seperate them and keep the volume equal, they will make 8psi at 90,000rpm. Half the amount they would with another turbo helping to ease the load. That assumes there are no variables of course.
It doesn't matter though i've totally messed up your thread and i apologise.
Tuesday, January 29, 2008 - 06:10 pm, by: Aska Liu(Icarus1314)
lol Luke, no problems man thanks to you now i understand how single / twin turbo works~ can drive my car atm tho, need to find a left mirror for it or the cops wont stop giving me trouble....mainly just need the back plate for the mirror.....ask everywhere... no one got them....sad.....
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, all i know is it reduce the turbo lag... 
