Questions about setting up Compound Turbos
12-02-2003, 07:33 PM
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Questions about setting up Compound Turbos
I've read alittle about the Compound Turbo set-ups some of the guys have been running and I was wondering how do you guys pick the turbo's? I'm not positive, but it seems as if you guys are choosing a smaller, quicker spooling turbo as the 1st stage then feeding this into a larger, higher volume turbo to get more air/boost. Is this correct? What are some simple rules or basic tips to chooseing the right parts for Compounding?
Also, what kinda boost levels do you start needing Compound turbos at?
Also, what kinda boost levels do you start needing Compound turbos at?
12-02-2003, 09:18 PM
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Re:Questions about setting up Compound Turbos
The large turbo is the primary. It feeds compressed air into the smaller one ( secondary)
The secondary turbo gets the exhaust pulse/flow first.
The secondary charger is named so because it compresses the air second, after the large turbo.
Atmo air is pulled into the large primary charger, compressed, and sent to the secondary turbo. Its actually not really compressed, but its a slang for what really happens. Its actually accelerated. Slung outward.
Sizing is not difficult, but depends on many factors: overall boost required, rpm range, application, VE of the engine (Its not what most think/feel), and the efficiency of the turbos you are trying to map for the job.
Budget comes in there somewhere too
Not exactly a 5 minute equation.
Don~
The secondary turbo gets the exhaust pulse/flow first.
The secondary charger is named so because it compresses the air second, after the large turbo.
Atmo air is pulled into the large primary charger, compressed, and sent to the secondary turbo. Its actually not really compressed, but its a slang for what really happens. Its actually accelerated. Slung outward.
Sizing is not difficult, but depends on many factors: overall boost required, rpm range, application, VE of the engine (Its not what most think/feel), and the efficiency of the turbos you are trying to map for the job.
Budget comes in there somewhere too
Not exactly a 5 minute equation.
Don~
12-02-2003, 10:48 PM
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Re:Questions about setting up Compound Turbos
So, if you wanted boost to come on early you would go with smaller, quicker spooling turbos? But if you wanted a wider range(like 1800-3500 rpms) you would have a smaller, quicker spooling one along with a larger turbo?
Also, the Primary Turbo is the first in the air flow line, but the last to actually provide additional air flow? IS this correct?
Besides Higher boost levels, is there any other advantage of Compound turbo's? Like, if you wanted about 55-60lbs of boost, would the compounds have the advantage of spooling up quicker than just a single larger turbo?
And the VE, that would have to be an estimate of what the engine will do after the modifications. Correct?
Also, the Primary Turbo is the first in the air flow line, but the last to actually provide additional air flow? IS this correct?
Besides Higher boost levels, is there any other advantage of Compound turbo's? Like, if you wanted about 55-60lbs of boost, would the compounds have the advantage of spooling up quicker than just a single larger turbo?
And the VE, that would have to be an estimate of what the engine will do after the modifications. Correct?
12-03-2003, 12:02 PM
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Re:Questions about setting up Compound Turbos
[quote author=Don M link=board=7;threadid=23175;start=0#msg217321 date=1070421524]
Not exactly a 5 minute equation.
Don~
[/quote]
Speak for yourself! :P
Not exactly a 5 minute equation.
Don~
[/quote]
Speak for yourself! :P
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12-04-2003, 01:23 AM
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Re:Questions about setting up Compound Turbos
Robert,
Yes if you want a faster spooling set of twins you can either go with smaller turbos or smaller exhaust housings. To have a wider range of use you will usually give up some midrange. Basically a small secondary and a large primary will give you midrange lag. Once again exhaust housing changes can fix some of this but not all if the size difference is extreme.
The primary draws air first and technically feeds the motor first. The reason being is that without the air being drawn into the primary the secondary wouldn't have air to feed the motor. But realistically the flow path is primary to secondary to motor.
The biggest benefit of twins is quicker spooling for the cfm. A large single is good for cfm but suffers on spoolup. The boost pressure is also a benefit. Efficientcy is another bonus. Most singles are run off the map to get high boost. That is not the case with twins. Ideally both turbo are running in a highly efficient portion of the map and providing cool high PR air.
Yes if you want a faster spooling set of twins you can either go with smaller turbos or smaller exhaust housings. To have a wider range of use you will usually give up some midrange. Basically a small secondary and a large primary will give you midrange lag. Once again exhaust housing changes can fix some of this but not all if the size difference is extreme.
The primary draws air first and technically feeds the motor first. The reason being is that without the air being drawn into the primary the secondary wouldn't have air to feed the motor. But realistically the flow path is primary to secondary to motor.
The biggest benefit of twins is quicker spooling for the cfm. A large single is good for cfm but suffers on spoolup. The boost pressure is also a benefit. Efficientcy is another bonus. Most singles are run off the map to get high boost. That is not the case with twins. Ideally both turbo are running in a highly efficient portion of the map and providing cool high PR air.
12-05-2003, 12:13 AM
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Re:Questions about setting up Compound Turbos
Hold on, now I'm confused. If the Primary is the larger turbo how does it "feeds the motor first," before the smaller secondary? Are you saying that it Feeds the Secondary Turbo, which then feeds the motor?
Here is what I have gotten so far:
Don M=
Priamary Turbo= Larger turbo, first in Airflow line from Airfilter,
Feeds boosted air into Secondary turbo.
Secondary Turbo= Smaller turbo, first in Exhaust flow from Engine, recieves air from Primary Turbo and increases boost
With this info, and knowing that Smaller Turbos normally spool up quicker than larger ones, and the smaller turbo that is place in the path of the exhaust flow before the Larger turbo, this is why I assumed that the Secondary turbo will be the first one to actually do any work. When I say this, I mean that the Secondary turbo is the one that will actually provide the initial boost when you step on the accelerator, and that the Primary turbo will then engage, feeding the Secondary turbo, which will then give you even higher boost numbers.
Is this correct? Or is it that the Larger Primary Turbo is spooling up before the Smaller secondary Turbo?
Here is what I have gotten so far:
Don M=
Priamary Turbo= Larger turbo, first in Airflow line from Airfilter,
Feeds boosted air into Secondary turbo.
Secondary Turbo= Smaller turbo, first in Exhaust flow from Engine, recieves air from Primary Turbo and increases boost
With this info, and knowing that Smaller Turbos normally spool up quicker than larger ones, and the smaller turbo that is place in the path of the exhaust flow before the Larger turbo, this is why I assumed that the Secondary turbo will be the first one to actually do any work. When I say this, I mean that the Secondary turbo is the one that will actually provide the initial boost when you step on the accelerator, and that the Primary turbo will then engage, feeding the Secondary turbo, which will then give you even higher boost numbers.
Is this correct? Or is it that the Larger Primary Turbo is spooling up before the Smaller secondary Turbo?
12-05-2003, 12:52 AM
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Re:Questions about setting up Compound Turbos
The smaller turbo will build boost first but drag the big turbo along with it. The big turbo has to be spinning fast enough to feed the required cfm to the little turbo. Basically the big turbo cant build boost until the smaller one does. There has to be back pressure/resistance to have boost.
Basically everything else is as you've stated.
Basically everything else is as you've stated.
spools first.
12-05-2003, 01:53 AM
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Re:Questions about setting up Compound Turbos
Ok now, Does haveing too large of a Primary turbo have a negagive effect on the response time of the secondary turbo?
12-05-2003, 10:00 AM
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Re:Questions about setting up Compound Turbos
12-05-2003, 05:25 PM
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Re:Questions about setting up Compound Turbos
[quote author=Robert Venable link=board=7;threadid=23175;start=0#msg218519 date=1070610795]
Ok now, Does haveing too large of a Primary turbo have a negagive effect on the response time of the secondary turbo?
[/quote]
What Nathan said-- it does. This is because the only air the the secondary can draw into its compressor comes from the compressor outlet of the primary. When the secondary first spools, it will actually create a partial vacuum in the crosstube (that connects primary compressor outlet to secondary compressor inlet) and that this partial vacuum will help to spool the large primary as the air rushes in to try to fill the partial vacuum.
But nothing's free. This partial vacuum makes a LOT of work for the secondary. That's why you won't get any boost from the sec until the primary is spinning. If the pri isn't turning, the sec is trying to make boost from a vacuum-- which won't happen.
The "compound" turbo setups are really a lot more closely linked (the two turbos) than would first appear to a casual observer. At least, that's how it was with me.
It will take me about a year to get the $$ and know-how to do a twins setup right. By then, there should be some good ball-bearing turbos out there that will make a twins setup REALLY interesting!!!!!!!!!!
Justin
Ok now, Does haveing too large of a Primary turbo have a negagive effect on the response time of the secondary turbo?
[/quote]
What Nathan said-- it does. This is because the only air the the secondary can draw into its compressor comes from the compressor outlet of the primary. When the secondary first spools, it will actually create a partial vacuum in the crosstube (that connects primary compressor outlet to secondary compressor inlet) and that this partial vacuum will help to spool the large primary as the air rushes in to try to fill the partial vacuum.
But nothing's free. This partial vacuum makes a LOT of work for the secondary. That's why you won't get any boost from the sec until the primary is spinning. If the pri isn't turning, the sec is trying to make boost from a vacuum-- which won't happen.
The "compound" turbo setups are really a lot more closely linked (the two turbos) than would first appear to a casual observer. At least, that's how it was with me.
It will take me about a year to get the $$ and know-how to do a twins setup right. By then, there should be some good ball-bearing turbos out there that will make a twins setup REALLY interesting!!!!!!!!!!
Justin
