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After reading this: http://www.gnttype.org/techarea/turbo/turboflow.html

I have found my answer. According to that, I was right with my hypothesis about temperature. I would be curious to know how much hotter a t-25 runs at a given psi than, say, a 50 trim. If anyone knows, it would be very nice to tell me. :)

Yes, volumetric efficiency hinders power, but that has nothing to do with what turbo is on the car.

It seems that the cfm is dependent soley on the volume of the engine and the RPM of the engine. And lbs/min depends on the pressure (which is the same on the big turbo and little turbo), the cfm (which is the same on big turbo and little turbo at a given PSI) and temperature (which is the only factor that changes due to turbo size).

I feel better :) I'm going to bed.
 

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-Compressor maps of various turbochargers.
-Volumetric Efficiency of the particular engine.
-Basic understanding of the behavior of non-ideal gasses as it pertains to pressure, volume and temperature.
 

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123212321 said:
I've read through countless explanations of CFM meanings and PSI meanings, and I still fail to understand how any of you make any sense.

PSI IS PSI. The only difference between a garden hose and a fire hose is the volume that is occupies. The fire hose has a stronger force because force is a direct representation of pressure over area. So obviously a big balloon will have more force due to its increase in area. Obviously a bigger hose will have more force due to its increase in volume.

My point is this: A 4663t combustion chamber is the same size no matter what turbo you are running. It has the same surface area, and is therefore subject to the same force when introduced to the same PSI. It is simple physics. :wall:

I think you all are very mislead in your thinking. Although this is just a hypothesis, I have yet to find an explanation that proves it wrong.

- A turbo is run using the exhaust energy of an engine. A bigger turbo is able to run the same PSI as a smaller turbo while converting less of that exhaust energy into direct heat loss. A bigger turbo becomes more efficient, therefore creating more power. This is the only explanation that makes any sense to me. Everyone's ability to pull the letters CFM out of their asses does not help me. It defies physics, and makes no sense. PLEASE SOMEONE SHED SOME EDUCATED LIGHT FOR ME!!!!!!!! I need this explained.

Edit: To put it another way, if you were to tell me what volume of air you had, and at what PSI the air was at - I could tell you exactly the amount of air you had. And since the volume of air in a combustion chamber is constant, a given PSI is going to be a constant mass of air! The only other variable that can control the amount of air present is temperature, which again leads me to my above conclusion that a bigger turbo makes more power at the same PSI soley due to a change in energy loss as heat. :)

basically everything you've touched on there, i had mentioned in my extremely simplistic explanation of a complicated subject, hence the quotations.

it is by no means a scientific paper on all the physics involved, merely just an easy way to explain the difference between a small and larger turbo to people with limited mechanical knowledge.

;)
 

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123212321 said:
My point is this: A 4663t combustion chamber is the same size no matter what turbo you are running. It has the same surface area, and is therefore subject to the same force when introduced to the same PSI. It is simple physics. :wall:
well thought out, except for the fact that when we speak of PSI we arent talking of cylinder PSI we're talking about intake pressure. Following your hypothesis you would also make the same power if you ran 20 psi through a vacuum hose to your TB as you would if you ran the 20 psi through a 3 in hard pipe. if your using a small intake tube you can up the boost all you want but the flow will hardly increase. These same principles apply to fuel systems. A fuel system will perfom better with larger (to an extent) lines and a stock pump than with stock lines and a higher pressure pump. thats a whole other can of worms though. ooh, i have an experiment for you to try to help you wrap your head around the whole cfm, psi pish posh. get a straw and breath through it, no matter how hard you blow or suck you still cannot get adequate FLOW to breathe comfortably. You cant apply simple physics to a complex subject if you dont take into consideration all the variables, and the appropriate circumstances for the given application.

all in all trying to force a bolt into a small hole wont work without tremendous pressure, what do you do then? make the hole bigger and the "flow" (bolt in hole)increases. haha crappy analogy but i was trying to simplify to a degree that would be understood by EVERYONE.
 

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I didn't read every post but there seems to be alot of mis-information. With everything else in the system staying constant, the reason a larger and more efficient wheel will flow more air at the same pressure level is because it produces less heat at the same psi than a smaller and less efficient wheel, colder air = more air.
 

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How do we maximize power on an internal combustion engine? You maximize the temperature difference between the air at the top of the cylinder and the bottom of the cylinder. Colder air = more air = more power. I still believe that 8psi on a 20g will produce a hell of a lot more power than 8psi on a 13g....it simply flows more cfm at 8psi. I mean once the pressurized air goes through the intercooler the air temp should be within a few degree's anyways, so what your left with is not a variation in the temperature but the actual amount of air at 8psi.
 

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Hondas typicaly run larger turbos for two reasons. 1. They have high compression and need to keep boost pressures low, and 2. they rev to 8k+ so they need a turbo that can flow up top.
 

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When did quick chic become a mod? Sorry but I havent been online in over a year cuz someone suspended me along time ago so I gave up on DSMTALK up untill about 3 moves and 2 motors. As far as the turbos go thats a good point. They flow the same amount of air at lower boost levels. I remember trying to hear my exgfs step dads deisel cummins turbo motor in his huge dodge truck. Couldnt hear it boost, but i knew it was there. That thing was huge.
 

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Discussion Starter #30
^^If you cant hear a Diesel spooling up...somethings terrible wrong. LOUD spoolage and 20+ psi stock...
 

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kornmstr1 said:
well thought out, except for the fact that when we speak of PSI we arent talking of cylinder PSI we're talking about intake pressure. Following your hypothesis you would also make the same power if you ran 20 psi through a vacuum hose to your TB as you would if you ran the 20 psi through a 3 in hard pipe. if your using a small intake tube you can up the boost all you want but the flow will hardly increase. These same principles apply to fuel systems. A fuel system will perfom better with larger (to an extent) lines and a stock pump than with stock lines and a higher pressure pump. thats a whole other can of worms though. ooh, i have an experiment for you to try to help you wrap your head around the whole cfm, psi pish posh. get a straw and breath through it, no matter how hard you blow or suck you still cannot get adequate FLOW to breathe comfortably. You cant apply simple physics to a complex subject if you dont take into consideration all the variables, and the appropriate circumstances for the given application.

all in all trying to force a bolt into a small hole wont work without tremendous pressure, what do you do then? make the hole bigger and the "flow" (bolt in hole)increases. haha crappy analogy but i was trying to simplify to a degree that would be understood by EVERYONE.
Thanks for taking the time to respond. Your talk about intake pressure makes sense - besides the fact that I'm not talking about an auto system in general, I'm talking about TURBOS! If I were to take the exact same engine, with the exact same intake pipes and layout - put a t-25 at 12 psi on it, dyno it, then do the same with a bigger turbo at 12 psi (ON the same engine, with the exact same intake pipes - the only variable change being the turbo), WHY would the larger turbo make more power.

I could be way off basis, but I hardly believe that the conditions produced by a turbo running at 12psi constitutes non-ideal gas laws. The only answer that still makes sense to me is energy loss as heat.
 

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dsms4ever said:
How do we maximize power on an internal combustion engine? You maximize the temperature difference between the air at the top of the cylinder and the bottom of the cylinder. Colder air = more air = more power. I still believe that 8psi on a 20g will produce a hell of a lot more power than 8psi on a 13g....it simply flows more cfm at 8psi. I mean once the pressurized air goes through the intercooler the air temp should be within a few degree's anyways, so what your left with is not a variation in the temperature but the actual amount of air at 8psi.
You just said over again exactly what I disproved using a source. CFM is only the product of the amount of air being moved in one rotation of the turbine by the SPEED of that turbine. At a given and non-changing PSI, a larger turbo spins slower because it pushes more air PER spin than a smaller turbo at the same PSI. CFM at a given PSI is CFM as a given PSI, no matter the turbo.

I'm convinced that CFM ratings on turbos are only meant to be MAXIMUM CFM ratings, because smaller turbos will eventually reach a point where they can no longer spin any faster and push any more air. But if the given PSI is low enough that it can be reached by both turbos, the only thing that enables a bigger turbo to push more lbs/min is the fact that it operates at a lower temperature due to its slower spin speed.

Like this: Let's say for the sake of the example that the CFM rating of a t-25 is 375 cubic feet per minute. Let's suppose that a 16g has a CFM rating of 500. If i subjected both turbos to a pressure of 12 PSI, both turbos would be pushing the same amount of cubic feet per minute of air. I don't know what that CFM would be, but it would be THE SAME NUMBER for both turbos.

Now, if I raised the boost of both turbos to 18 PSI (theoretically speaking), the t-25 would now be outflowed by the 16g, because it's maximum CFM has been reached and surpassed, while the 16g still pushes more air per revolution of the turbo and therefore has a higher maximum CFM.
 

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123212321 said:
Thanks for taking the time to respond. Your talk about intake pressure makes sense - besides the fact that I'm not talking about an auto system in general, I'm talking about TURBOS! If I were to take the exact same engine, with the exact same intake pipes and layout - put a t-25 at 12 psi on it, dyno it, then do the same with a bigger turbo at 12 psi (ON the same engine, with the exact same intake pipes - the only variable change being the turbo), WHY would the larger turbo make more power.

I could be way off basis, but I hardly believe that the conditions produced by a turbo running at 12psi constitutes non-ideal gas laws. The only answer that still makes sense to me is energy loss as heat.

It would then depend on if the engine was capable of using the full volume of air that the t-25 was putting out and more. If it could flow more than the t-25 was putting out then putting the larger turbo on it with more volume would be a benefit as long as the engine could move the added volume from the bigger turbo through it.
 

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This is precisely why it's dumb to ask someone how much boost their car runs without knowing anything about the size of the compressor.
 

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Well since someone resurrected this thread, I figure I'll throw my two cents in. At one time I had three 1G turbo AWD cars. One was an automatic with a stock tiny turbo. That car was almost always under some boost because it spooled up so quickly. It was like I was driving a V6. Not as much fun as a manual tranny but that the little turbo definitely got a work out. It eventually failed under warranty and the dealer (claimed they) couldn't get the exact turbo and replaced it with a slightly larger turbo usually used on a Volvo. I could definitely feel the difference - there was a lag when none was noticeable before. I still have a 5 speed 92 Talon Tsi with a big 16G TRE running at 15psi provides gobs more power but with a lag.
 
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