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?
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
To figure out how it works, visit www.howstuffworks.com
I'm sure they have a section on turbochargers.
what about like when people say they're running like 12 psi? what does that mean?
someone tell me plz!
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. :banghead:
I learn something new everyday.
Not from me, I don't help anybody... Just ask DildoRida67.
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.
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.
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.
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).
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.
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. :roll:
Correct me if I'm wrong. Would'nt the measurment of pressure with the addition of a turbocharger or supercharger start after 14.7psi. Because if a car is at sea level then there would allready have to be 14.7psi of ambient air pressure within the intake manifold upon the intake stroke.
The gauge already has 14.7 psi acting on the bellows, so you will be
reading differential pressure wrt atmosphere, thus we use the acronym psig
in the egineering game.
When working out your density ratios, pressure ratios and volumes you work in absolute, just as you would for ideal gas equations.
Makes sense, thats how a gauge can read below 0 bar.
Ahh my favorite Pv=nRT :hi: .
Beware the bar measurement too. Some instruments are rounded to 100kPa for
bar instead of the 101.32kPa, not that it matters too much on a car
People can get a bit too cute when it comes to huffered or hairdryered engines.
I do not disagree.
As at the outlet side there must be a high pressure which can then expand as the restrictions allow. If the intake manifold is pressurized at 5 psig than the total pressure at the outlet of the compressor must be higher for more air to enter the manifold.
This is true for the static pressure but what about dynamic pressure?
Maybe I could mail you my pitot-static tube? :roll:
You are alluding to Tp= Vp + Sp ?
Yea originally I thought I just might be miss-understanding what pressure vwhobo was referring too. But now I honestly do not know what direction the discussion is taking, off topic I guess.
I think he is simplfying it so that people with only a bourdon gauge can
appreciate that although the pressure reading (static pressure) may be high
the flow may be correspondingly low due to pressure loss of the
Not many people would be able to pitot traverse the pipes to see total pressure and work out velocity pressure.
Thanks for the clarification.
'sOK. Of course if the pressure is taken at the plenum a lot of that concern is nullified and becomes more or less a question of post TB VE.
This kid couldnt understand what people were talking about when they
"hey, im running 8 pounds on my integra"
Hes going to came back and check the post, read all this stuff you guys are talking about, and his head is going to explode...But then again I think this thread kinda veered away from the original question, so he probably wont care.
He asked the price of an apple and came away with a cornucopia :wink2: I would say that was money well spent.
Yes its the differential pressure. When the throttle plates are closed the
gauge says inches of mercury so the higher the inches, the lower the
pressure. When you're not under boost, it's just a regular N/A motor,
producing vacuum to suck in air and make power. When you give it some
throttle, it's at 0, that means there is no longer just engine vacuum, it's
at a steady flow of air (meaning the turbo is producing just as much air as
the engine is sucking, then there is booost where the turbo is actually
forcing high speed air into the combustion chambers like vwhobo said.
But what I'm confused about is if the psig measures the relative psi in the manifold, than doesnt the air get more compressed as it goes into the combustion chambers because of its velocitty? than the gauge is not that accurate and so does the wastegate. cuz the wastegate uses pressure in the manifold so it wouldnt be accurate right?