intercooling between stages
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seeker1056
gear head
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I ran air/water between stages on my twins set and an air/air after the turbos
Turning it off, then turning it on made about 5 psi more boost due to the cooler air
Turning it off, then turning it on made about 5 psi more boost due to the cooler air
Care to share the rough sizes of the turbos and intercoolers?
seeker1056
gear head
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was an hx35 and the larger hx55 for which I forget the specs now
That's fine...just trying to get a rough idea on size.
If you cool interstage, then all else constant, your second stage can be smaller and do the same job.
An intercooler is nothing but a thermal turbocharger. A turbo compresses air mechanically, and an intercooler does it thermally. There is a density ratio across an intercooler just the same as across a turbo.
An intercooler is nothing but a thermal turbocharger. A turbo compresses air mechanically, and an intercooler does it thermally. There is a density ratio across an intercooler just the same as across a turbo.
JOHNBOY
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Great explanation! Basically they do the same thing. Improve charge density.
Jim Fulmer
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Ran into a puller running a A/W and he is seeing 70 degrees at the intake with a small intercooler, now looking at the gasser world I don't think there is more power from 70 to 40 degrees.........opinions!
Jim
Jim
Makes sense.
When I started this thread, I wanted it to turn into a thermal discussion. I have some reservations about running two intercoolers (one after each stage) as opposed to running one after the second stage. I need to recollect my thoughts though.
One thing you should keep in mind is that the internal airflow requirements of the core will be substantially higher when used interstage, as the volume flow will likely be multiple times higher interstage relative to what it is after the second stage.
But an inlet and outlet pressure gauge can tell you that story in seconds with a little quick trial and error testing for pressure drop across the core.
I think I'm missing something here....
Isn't the volume of air the setup can move equivalent to whatever the primary is capable of moving? The second stage just increases the pressure and subsequently temperature - not decreasing volume.
I can understand that if you want a smaller secondary to light at a lower RPM for instance, you are sacrificing overall performance on the "high end" due to the heat addition of the air in the smaller secondary. So if you were to run a large secondary lets say maybe 2.5/2.8 or 2.6/2.8, you are not heating the air up as much if you were feeding a stock charger, but the pressure has to be less than with a smaller secondary (assuming constant volume).
If the above statements are true, then:
1. A larger secondary requires less intercooling (inter-stage or post-secondary) to be as effective as a small secondary assuming the same primary.
2. The setup with a larger secondary would move the same air at a lower pressure and temperature than a setup with a smaller secondary.
Correct me if I am wrong please.
It's not immediately intuitive, but the answer is no. The volume flow through the system is not constant. Not even close. Each compressor (whether mechanical [turbocharger] or thermal [intercooler] ) reduces the volume flow rate of the system by compressing the charge air stream into s smaller space.... decreasing it's volume. And since mass flow is constant, and you are decreasing the volume, the volume flow must come down. And since density is mass/volume, this makes perfect sense, as the entire point of forced induction is to increase charge air density. More mass in the same space.
If you need proof of this, just think about it.
A 360 cubic inch engine displaces 360 cubic inches every two revs (we're assuming 100% VE here for simplicity). Well, if it displaces 360 cubic inches every two revs, and it's spinning say, 3000rpm, then it's displacing 312 CFM.
The key thing to make your mind accept is that there is literally only 312 CFM worth of space available inside that engine. Unless you swell the cylinder walls it's not getting any bigger. Ever.
As boost climbs, that number..... does nothing.... it's always 312 CFM at 3000rpm at 100% VE. Boost does not change the volume of air moving through an engine. It changes the density of that airflow. If the volume increased, then you'd have to ask yourself, where the hell did it go then? Cause again.... the engine doesn't swell up when it comes under boost. Well, sometimes they do, but that involves a bunch of coolant and oil all over the ground.
Okay.... so we're good I hope. A 360 cubic inch engine is going to displace 312 CFM at 3000rpm and 100% VE all day, any day forever. No more, no less.
Now look at what your turbocharger is bringing in.... If it's a decent set of compounds you're talking 2000ish CFM coming in that thing. The fact that you can have this much and more volume flow coming in and not have any more than 300 some odd CFM moving through the engine is proof that the volume flow decreases dramatically throughout the system. The volume flow decreases proportionate to the density ratio the system achieves from first stage to intake manifold, including all intercooling.
Correct. If the second stage is capable of higher volume flow (larger wheel) then you do not need as high a density ratio between stages through intercooling to allow all the air from the first stage to "fit" through the second stage. Not coincidentally this is largely based on the same concept of dynamic system volume flow I touched on above.
The only way to move more air mass by altering the second stage is by increasing the density ratio across the second stage either by increasing the PR for any given efficiency, or by increasing efficiency for any given PR, or both.
It's not a case where bigger is always better. If the bigger compressor starts slipping off of efficiency toward the surge line and a smaller one stays nearer the highest efficiency islands then the smaller compressor will rank a higher density ratio for any given PR and mass flow.
I guess I can't answer your last question in a general way. It's a question that must be answered for a specific scenario.
Or if not, I'm not bright enough, or familiar enough with the concepts to see how to generalize it right now.
Thanks for clearing that up ... I should have re-read my post. I had the right concept at the end...should have had that at the beginning.
Definitely gives me something to think about.
Here's a little compilation to show what happens to volume as forced induction takes place.
For starters, here's the volume of the engine, vs the volume of atmosphere we want inside it.
And here's the mass of the intake air charge we want to compress into that engine:
Here's the mass of the volume we started with inside the N/A engine:
So how do we get the mass of oxygen molecules we want inside a space they clearly will not fit into???
We Compress the sh*t out of them...
Here's my Case "compressor" simulator at rest, with the charge air at atmospheric pressure:
And this would be the volume of the intake air charge after passing through the first stage compressor:
After passing through the interstage cooler:
After passing through the second stage compressor:
And after passing through the second stage cooler:
Okay.... so what have we done? We've compressed it. Reduced the volume. What about mass?
Well, lets check...
Nope, mass stayed the same, just volume that decreased. Same mass, less volume equals more dense. We've increased the density, the whole point of forced induction and intercooling. Same mass into a smaller space that we can then fit into the engine.
Speaking of which...
We've done it! We've managed to stuff waaaaaaaay more air into that engine. But more air volume???? Of course not. The engine box never changed size. We took a large volume and mass and compressed the volume down to that of the engine so it would "fit". And increased density in the process.
Or did we? Well lets check....
Yep. The mass went up tremendously. The gauge is 180* out from where it was N/A but the engine volume never changed. The beauty of forced induction. The ability to take the mass of a much larger volume of air, and compress it down to the volume of your engine so you can have all the mass in a much smaller space.
For starters, here's the volume of the engine, vs the volume of atmosphere we want inside it.
And here's the mass of the intake air charge we want to compress into that engine:
Here's the mass of the volume we started with inside the N/A engine:
So how do we get the mass of oxygen molecules we want inside a space they clearly will not fit into???
We Compress the sh*t out of them...
Here's my Case "compressor" simulator at rest, with the charge air at atmospheric pressure:
And this would be the volume of the intake air charge after passing through the first stage compressor:
After passing through the interstage cooler:
After passing through the second stage compressor:
And after passing through the second stage cooler:
Okay.... so what have we done? We've compressed it. Reduced the volume. What about mass?
Well, lets check...
Nope, mass stayed the same, just volume that decreased. Same mass, less volume equals more dense. We've increased the density, the whole point of forced induction and intercooling. Same mass into a smaller space that we can then fit into the engine.
Speaking of which...
We've done it! We've managed to stuff waaaaaaaay more air into that engine. But more air volume???? Of course not. The engine box never changed size. We took a large volume and mass and compressed the volume down to that of the engine so it would "fit". And increased density in the process.
Or did we? Well lets check....
Yep. The mass went up tremendously. The gauge is 180* out from where it was N/A but the engine volume never changed. The beauty of forced induction. The ability to take the mass of a much larger volume of air, and compress it down to the volume of your engine so you can have all the mass in a much smaller space.
Last edited:
Big Blue24
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Charles,
That explanation was "over-the-top"!
Easy to understand.
Funny as heck.
It was also educational.
That explanation was "over-the-top"!
Easy to understand.
Funny as heck.
It was also educational.
94 12valve
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x2 very well done Charles :clap: