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Old 03-19-2005, 12:44 AM   #1
silvia_star
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dont understand the # of pounds boost???

what does it mean when people say they are running like 10 pounds of boost? how does it work out? how do you change the amount of boost?
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Old 03-19-2005, 05:22 AM   #2
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Quote:
Originally Posted by silvia_star
what does it mean when people say they are running like 10 pounds of boost? how does it work out? how do you change the amount of boost?

boost. PSI. Bars. All refer to the ammount of pressure a turbo/supercharger is putting out. Boost can be changed via boost controllers, and other ways also.

To figure out how it works, visit www.howstuffworks.com

I'm sure they have a section on turbochargers.
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Old 03-19-2005, 07:52 PM   #3
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what about like when people say they're running like 12 psi? what does that mean?
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Old 03-19-2005, 07:57 PM   #4
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someone tell me plz!
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Old 03-19-2005, 08:29 PM   #5
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Quote:
Originally Posted by Godlaus
boost. PSI. Bars. All refer to the ammount of pressure a turbo/supercharger is putting out. Boost can be changed via boost controllers, and other ways also.

To figure out how it works, visit www.howstuffworks.com

I'm sure they have a section on turbochargers.
No, no, no, no, NO! I have explained this previously on these forums. Turbochargers in and of themselves DO NOT create pressure. Turbochargers produce increased airflow. It is the fact that this increased airflow is then restricted by flowing into the intake manifold and into the combustion chambers that creates pressure or boost.

Here is a perfect example. Everyone has a blow dryer in their house. Go get it and plug it in. Turn it on. How much pressure is it putting out. None. Zero. Zilch. Nada. Now cup your hand and put it about a foot in front of the nozzle. Do you feel a little pressure? That's because there is a little airflow restriction. Now move your hand closer. More pressure? More restriction. Closer still. More pressure? More restriction. And so it goes until you reach the mechanical or dynamic limits of the machine.

The boost numbers that you read are based on the ratio of airflow verses restriction. Obviously a pop off valve, wastegate, boost controller, etc will reduce pressure at the appropriate time because... If you have enough turbine speed, therefore enough airflow AND at the same time enough airflow restriction the boost pressure will keep building until you reach the mechanical or dynamic limits of the turbo or something blows up. That something will be the engine because turbo housings can withstand in excess of 50 psi.

Please guys, let's try to keep this simple, correct and real.
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Old 03-19-2005, 08:35 PM   #6
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Quote:
Originally Posted by vwhobo
The boost numbers that you read are based on the ratio of airflow verses restriction. Obviously a pop off valve, wastegate, boost controller, etc will reduce pressure at the appropriate time because... If you have enough turbine speed, therefore enough airflow AND at the same time enough airflow restriction the boost pressure will keep building until you reach the mechanical or dynamic limits of the turbo or something blows up. That something will be the engine because turbo housings can withstand in excess of 50 psi.

Please guys, let's try to keep this simple, correct and real.

I learn something new everyday.
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Old 03-19-2005, 08:37 PM   #7
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Originally Posted by Godlaus
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Not from me, I don't help anybody... Just ask DildoRida67.
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Old 03-20-2005, 12:10 AM   #8
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Quote:
Originally Posted by vwhobo
No, no, no, no, NO! I have explained this previously on these forums. Turbochargers in and of themselves DO NOT create pressure. Turbochargers produce increased airflow. It is the fact that this increased airflow is then restricted by flowing into the intake manifold and into the combustion chambers that creates pressure or boost.

Here is a perfect example. Everyone has a blow dryer in their house. Go get it and plug it in. Turn it on. How much pressure is it putting out. None. Zero. Zilch. Nada. Now cup your hand and put it about a foot in front of the nozzle. Do you feel a little pressure? That's because there is a little airflow restriction. Now move your hand closer. More pressure? More restriction. Closer still. More pressure? More restriction. And so it goes until you reach the mechanical or dynamic limits of the machine.

The boost numbers that you read are based on the ratio of airflow verses restriction. Obviously a pop off valve, wastegate, boost controller, etc will reduce pressure at the appropriate time because... If you have enough turbine speed, therefore enough airflow AND at the same time enough airflow restriction the boost pressure will keep building until you reach the mechanical or dynamic limits of the turbo or something blows up. That something will be the engine because turbo housings can withstand in excess of 50 psi.

Please guys, let's try to keep this simple, correct and real.

Ok wvhobo, turbos use centrifugal force right, which increases the speed of the air going into the cylinders. So most of the PRESSURE BUILD UP IN THE CYLINDERS because thats when the air gets restricted by the intake valves right? When the compresser is spinning, more velocity of air if going into the engine so if the intake valve is closed, than pressure build up there and when the valves open, the air is already pressured to fill the combustion cambers. Am I right that when the velocity of the air meets a closed intake valve or top of a piston, the velocity is turned into pressure?
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Old 03-20-2005, 12:12 AM   #9
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Originally Posted by CarEXPERT
Ok wvhobo, turbos use centrifugal force right, which increases the speed of the air going into the cylinders. So most of the PRESSURE BUILD UP IN THE CYLINDERS because thats when the air gets restricted by the intake valves right? When the compresser is spinning, more velocity of air if going into the engine so if the intake valve is closed, than pressure build up there and when the valves open, the air is already pressured to fill the combustion cambers. Am I right that when the velocity of the air meets a closed intake valve or top of a piston, the velocity is turned into pressure?
Based on this post I would say you have a pretty good grasp on the subject.
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Old 03-20-2005, 06:10 AM   #10
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Quote:
Originally Posted by silvia_star
what does it mean when people say they are running like 10 pounds of boost? how does it work out? how do you change the amount of boost?

They are using slang. They are saying the pressure is 10 psig (pounds per square inch gauge), which simply means relative to atmospheric pressure is 10 psi. Saying "pounds" sounds pretty tough and knowledgable though.

When listening to your mates carry on, remember that some measure at the diffuser of the compressor, others before the throttle body and others at the plenum or intake runners. The plenum is where a map sensor is generally located and where you should measure for bragging rights.
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Old 03-20-2005, 06:24 AM   #11
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yeah

carexpert, what you said is correct except the part about centrifugal force. the turbine spinning simply moves air, as a fan does, there is no centrifugal force involved. centrifugal force pertains to the force exerted on any part of the turbine by it's rotation. what we are concerned about is the air coming off the turbine, and entering the intake or exhaust
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Old 03-20-2005, 06:35 AM   #12
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Originally Posted by carls47807
carexpert, what you said is correct except the part about centrifugal force. the turbine spinning simply moves air, as a fan does, there is no centrifugal force involved. centrifugal force pertains to the force exerted on any part of the turbine by it's rotation. what we are concerned about is the air coming off the turbine, and entering the intake or exhaust
Well actually compressor side is a centrifugal pump. It's all very basic fluid dynamics kind of stuff. The intake air is pulled into the center and flung (for lack of a better description) o-utward by the rotation of the blades. Centrifugal force in action.

Note: O-utward is spelled as such because the language filter won't let it through written properly. Try it.
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Old 03-20-2005, 06:36 AM   #13
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Quote:
Originally Posted by vwhobo
No, no, no, no, NO! I have explained this previously on these forums. Turbochargers in and of themselves DO NOT create pressure. Turbochargers produce increased airflow. It is the fact that this increased airflow is then restricted by flowing into the intake manifold and into the combustion chambers that creates pressure or boost.

Here is a perfect example. Everyone has a blow dryer in their house. Go get it and plug it in. Turn it on. How much pressure is it putting out. None. Zero. Zilch. Nada. Now cup your hand and put it about a foot in front of the nozzle. Do you feel a little pressure? That's because there is a little airflow restriction. Now move your hand closer. More pressure? More restriction. Closer still. More pressure? More restriction. And so it goes until you reach the mechanical or dynamic limits of the machine.

The boost numbers that you read are based on the ratio of airflow verses restriction. Obviously a pop off valve, wastegate, boost controller, etc will reduce pressure at the appropriate time because... If you have enough turbine speed, therefore enough airflow AND at the same time enough airflow restriction the boost pressure will keep building until you reach the mechanical or dynamic limits of the turbo or something blows up. That something will be the engine because turbo housings can withstand in excess of 50 psi.

Please guys, let's try to keep this simple, correct and real.

What makes you think that the compressor on a turbocharger cannot raise the pressure of the air at the outlet with respect to the inlet?

I am assuming that you are referring to the outlet static pressure component being lower than the inlet total pressure which may in fact be true (for a given scenario). However, the outlet total pressure is going to be the sum of the outlet static and dynamic pressure components. The outlet total pressure must be higher than the inlet total pressure otherwise all the shaft work going into the compressor is for nothing.

As for the hair dryer it employs a low cost fan which is not design to generate high pressures to begin with. Nevertheless, the total pressure in the hair dryer is higher than atmospheric pressure otherwise the air would not flow out of the hair dryer (high pressure always moves towards a low pressure).
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Old 03-20-2005, 06:40 AM   #14
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The compressor does not have a turbine. it has an impellor that approximates a mixed flow fan (centifugal + axial). The contours of the impellor blades create a high pressure region, until they enter a choke region where stall flutter starts.

Even when there is no connection to the discharge snout, there will be a higher pressure in the diffuser than atmosphere, because of pressure drop.
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Old 03-20-2005, 06:45 AM   #15
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Quote:
Originally Posted by Regular.Stormy
What makes you think that the compressor on a turbocharger cannot raise the pressure of the air at the outlet with respect to the inlet?

I am assuming that you are referring to the outlet static pressure component being lower than the inlet total pressure which may in fact be true (for a given scenario). However, the outlet total pressure is going to be the sum of the outlet static and dynamic pressure components. The outlet total pressure must be higher than the inlet total pressure otherwise all the shaft work going into the compressor is for nothing.

As for the hair dryer it employs a low cost fan which is not design to generate high pressures to begin with. Nevertheless, the total pressure in the hair dryer is higher than atmospheric pressure otherwise the air would not flow out of the hair dryer (high pressure always moves towards a low pressure).
You can only have pressure if you have restriction. The nozzle pressure is in fact slightly higher than the inlet pressure, but... Keep in mind the true inlet pressure is negative due to the the fact the impeller is spinning which explains the differential. Also keep in mind that the nozzle has high velocity air flow and as we all learned in 5th grade higher velocity equals lower pressure.

As for the hair dryer analogy, if you're honestly trying to equate the two this subject is above your head. Perhaps I should have said perfect example for those of us not fortunate enough to have a manometer and a turbo laying around the house.
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