Calculate total lb/min air on a compound setup

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JD7520

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If I have a compound turbo setup and atmospheric turbo makes 150 pounds per minute and secondary turbo will make 85 pound per minute, what is the final pound per minute of flow at the manifold?

I was expecting it to still just be 150 pounds per minute as the secondary just compresses the air further. But I have read some other people add the two together 150+85=235. The only way that would make sense to me would be if the secondary turbo was pulling air away from the primary that it caused it to flow more.

So which is it?!?!?
 
150

Not certain the pictures are still there, but this was a great thread to explain mass flow vs. volume

http://competitiondiesel.com/forums/showthread.php?p=1105407#post1105407

have fun



JD7520 said:
If I have a compound turbo setup and atmospheric turbo makes 150 pounds per minute and secondary turbo will make 85 pound per minute, what is the final pound per minute of flow at the manifold?

I was expecting it to still just be 150 pounds per minute as the secondary just compresses the air further. But I have read some other people add the two together 150+85=235. The only way that would make sense to me would be if the secondary turbo was pulling air away from the primary that it caused it to flow more.

So which is it?!?!?
Click to expand...
 
Don't matter what you use as a secondary turbo....the primary will only flow what it's rated for.
Where would the secondary get "Extra" air from? It all comes through the primary....
 
The total flow is based on whatever the large turbo is. The smaller turbo is more of an intermediate airflow device, so that you don't have to try to run a large single at 100psi to make power. Instead of a pressure ratio of like 7:1 (which usually results in a broken turbo) you can have say, 3.5:1, and then 2:1 through the small turbo.

So, same result, just spools a lot sooner, and is easier on parts. There are turbos out there that will survive 100psi as a single, they're usually about $8K and start spooling around 3000rpm, which isn't so good for anything other than sled pulling.

Clear as mud?
 
Agreed. Less than 150lbs/min. Think of your secondary as an air restriction more than anything. Your primary would make more peak power without it. You toss the secondary on just to broaden the powerband and make it into usable power.
 
CorneliusRox said:
Agreed. Less than 150lbs/min. Think of your secondary as an air restriction more than anything. Your primary would make more peak power without it. You toss the secondary on just to broaden the powerband and make it into usable power.
Click to expand...

Yeah, that's what I've seen too. Did a turbo test a couple years ago with a 71mm as a single, and 57/71mm compounds, and the single made 30hp more up top at the same boost (60psi).

In the end, the truck was way more fun and drivable with the 57/71 twins, so that's what stayed on it.
 
Thanks to all for clearing this up. That is what I thought, but wanted to make sure.
 
We are trying to get a triple or quad setup to make 450 lb/min. Thinking about two K44 for primary. Or three S500sx. Any suggestions? Need to be at 100 pounds boost at that volume.
 
That's a lot of air. What HP range are you shooting for?
 
JQmile said:
That's a lot of air. What HP range are you shooting for?
Click to expand...

I've always heard about 10hp per every lbs/min of air if you've got the fuel, so... 4500hp? Seems excessive. Also at only 100psi, it has to be the best flowing head ever!
 
CorneliusRox said:
I've always heard about 10hp per every lbs/min of air if you've got the fuel, so... 4500hp? Seems excessive. Also at only 100psi, it has to be the best flowing head ever!
Click to expand...

That's pretty close for flywheel horsepower based upon what I've seen. I wonder what the application is? How about some more info original poster?
 
Ok so what about triple turbos? For example an s472 secondary with 2 s366 primaries.

Would you just add up each s366 and that would be the total lbs/min? Or is it not that simple?
 
mike diesel said:
Ok so what about triple turbos? For example an s472 secondary with 2 s366 primaries.

Would you just add up each s366 and that would be the total lbs/min? Or is it not that simple?
Click to expand...

It is that simple. The size of the secondary is where / how it will compound.
 
JQmile said:
The total flow is based on whatever the large turbo is. The smaller turbo is more of an intermediate airflow device, so that you don't have to try to run a large single at 100psi to make power. Instead of a pressure ratio of like 7:1 (which usually results in a broken turbo) you can have say, 3.5:1, and then 2:1 through the small turbo.

So, same result, just spools a lot sooner, and is easier on parts. There are turbos out there that will survive 100psi as a single, they're usually about $8K and start spooling around 3000rpm, which isn't so good for anything other than sled pulling.

Clear as mud?
Click to expand...


I am not saying you are wrong since I don't actually know chit about turbochargers in the grand scheme.


A single s475 can make 800hp+ in a single configuration but in most compound setups things get out of control in a hurry as far as boost numbers and heat before you approach that number.

Is it because of the restraints on the secondary used typically in s475 setups? An s363 over an s475 vs maybe an s366 over an s475 for example?


I have to say compounds definitely appear to be harder on parts as well. Transmissions, rods, cranks, etc. appear to suffer with the low rpm power compounds usually present.
 
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