boost question

alright so ive had this question for a while and havent been able to figure it out. how is boost pressure different from supercharger to supercharger? for example, if you have an eaton m45 and an m90 and theyre both pushing 7psi, will the m90 be flowing more air? the first thought would be that since the eaton m90 flows twice as much air per revolution that it would then be flowing twice as much air at 7psi. but that doesnt seem possible, how can you have the exact same amount of pressure with twice the airflow? so then that means that to achieve the 7psi, the m90 must be rotating half the speed of the m45? will the m90 make more power than the m45 at 7psi?

also, since the amount the supercharger flows increases as rpms increase, then how do you have a pulley that "sets" the amount of boost you run? as the engine revolutions increase shouldnt the amount of boost?

psi does not measure volume.

Good question, I will let the other guys awnser.

I also had the same question awhile back and read a really good page explaining it. I can't explain it myself, but i can explain your pulley question. Even though a pulley will produce more boost than another, they are both limited by what the blow off valve allows them to produce. lets say you have a centrifugal blower making 6 psi. You then add a different pulley that is capable of 10 psi. The supercharger is now making 10 psi, but it is beeing "bled" out of the system via the blow off valve (BOV) back down to 6psi. If you want more boost you can adjust the BOV (some have a dial, others require stiffer springs).

Boost pressure is irrelevant, but airflow is not. Positive displacement blowers are hard to explain, but yes the bigger blower will make more power at the same power, more power at less boost. A pulley for a positive displacement blower basically dictates the amount of airflow going into the motor, and the reistance put forth by the motor determines the boost level. That's why if you run the same S-trim pulley on a 302, or a 302 with AFR 185's and a victor 5.0 intake the one with heads will see a few pounds less boost, but make more power.

yes i get all these concepts. but the amount of air a supercharger flows and the pressure within the intake manifold are directly related to one another. with the engine setup remaining constant, a certain amount of air in the intake track will provide a certain amount of pressure pushing outward... aka Xairflow=Xpsi, at least thats how i understand it. so therefore no matter what the supercharger size, to attain a certain psi within the intake manifold you have to flow a certain amount of air. so therefore 13psi is 13psi so it doesnt matter what supercharger your using, youll always make the same amount of power because youll always be flowing the same amount of air. the only way i can see one supercharger making more power than anohter supercharger at the same boost level would be if one were more efficient, be it operating at a lower temperature or requiring less power to turn the rotors. as for blow off valves setting boost level, as i understand it thats a poor practice, maybe im wrong. seems like it would just be needless work being put thru the supercharger. lacking a description on this thread, can someone at least point me to a site that can explain this?

No, you apparently havn't grasped it.

IE, fastest LT1 car in the world (best example I could think of :p) has gone low 8's at over 170 MPH. Turbo? 98MM large frame, at 23 pounds of boost. Now, a 98MM turbo isn't grossly efficient at 23 pounds of boost, it's actually quite low on the map, but do you think even a big turbo like a T76 would make that kind of power at 23 psi, even though 23 psi into a motor like that is right at the peak of the T76's efficiency island? No, because it doesn't move the same amount of air at 23 psi as a bigger turbo/compressor does.

So when trying to understand turbos/blowers, throw that boost pressure shit all the way out the window because it doesn't mean shit for understanding why bigger blowers make more power. An M90 moves 90 cubic inches of air per revolution. An M45 moves 45 inches, simple. So, you need to spin the M45 roughly twice as fast to move the same amount of air into the motor. Spinning that blower twice as fast not only causes a power loss due to extra heat produced and drag on the crankshaft, but the blower is spinning faster, and has to work much harder to keep up with the motor. Faster moving blower = faster rotors, which means the air is compressed more for the given volume. It's hard to explain and I'm not the best at it. Talk to a SAE person, they'll lay it out easy. Either way you cut the cake, for equal boost pressures the larger blower is moving more air and making more power.

anyone have a link that can explain this to me?

anyone have a link that can explain this to me?

Buy a book, Corky Bell's Maximum Boost.

boosted331 explained it pretty simple terms, if you want to get a more tech explaination, buy that book. It goes into great detail of what you want to know.

well i already own supercharged by corky bell and that doesnt really explain it. it doesnt make sense to me that you can be pushing more air but still be producing the same amount of pressure? i mean whats the point of even talking about it in terms of boost, why wouldnt people talk about it in terms of airflow?

Bigger blower(m90) = less revolutions to = desired psi
Smaller blower(m45) = more revoultions/ more strain on the engine/ more heat generated to = same desired psi

PSI being regulated by the BOV

So the m90 takes less revolutions to = desired psi which means it is more efficent because it takes less power from the engine to generate the same power as the m45

so then 13 psi on an m90 will flow the same amount of air as 13 psi on an m45

so then 13 psi on an m90 will flow the same amount of air as 13 psi on an m45

No, because the motor poses more of a restriction to the M40 than the M45. 13 psi on an M90 is a lot more power than on an M45.

How about this... you have a 5 gallon air compressor tank, and a 30 gallon air compressor tank. Fill them both to 10psi. Which one has more air in it? Obviously the 30 gallon. Same pressure, different volume. More air means more power.
A certain engine(say, a 5.0L ford v8) can only take in so many cubic feet of air per revolution. Lets say for our imaginary engine that this is 500cfm. Now we put a supercharger on the car, running 1 bar of pressure(twice the atmospheric pressure - twice as much air molecules in a cubic foot). With the engine taking in 500cfm of air at 1bar pressure, the supercharger will be taking in 1,000cfm of air at 0 bar pressure. Volume and pressure.
Now lets take an imaginary 2.5L engine that can take in 250cfm. Slap a supercharger on that, running 1 bar as well. Double the pressure, double the airflow, the supercharger is taking in 500cfm. Same pressure, different volume. Different power output.
Ultimately, it all comes down to how much air your engine can take in, in a given ammount of time (cubic feet per minute, cfm). This is the ultimate goal. Pressure(psi) is just another measurement of an engine's system. It is difficult to measure CFM, so people use pressure(easy to measure) so people can get a general idea of how much air the engine is taking in. Combine pressure, engine displacement, and engine redline, and I'd have a good general idea of how much power the engine is making.

How about this... you have a 5 gallon air compressor tank, and a 30 gallon air compressor tank. Fill them both to 10psi. Which one has more air in it? Obviously the 30 gallon. Same pressure, different volume. More air means more power.
A certain engine(say, a 5.0L ford v8) can only take in so many cubic feet of air per revolution. Lets say for our imaginary engine that this is 500cfm. Now we put a supercharger on the car, running 1 bar of pressure(twice the atmospheric pressure - twice as much air molecules in a cubic foot). With the engine taking in 500cfm of air at 1bar pressure, the supercharger will be taking in 1,000cfm of air at 0 bar pressure. Volume and pressure.
Now lets take an imaginary 2.5L engine that can take in 250cfm. Slap a supercharger on that, running 1 bar as well. Double the pressure, double the airflow, the supercharger is taking in 500cfm. Same pressure, different volume. Different power output.
Ultimately, it all comes down to how much air your engine can take in, in a given ammount of time (cubic feet per minute, cfm). This is the ultimate goal. Pressure(psi) is just another measurement of an engine's system. It is difficult to measure CFM, so people use pressure(easy to measure) so people can get a general idea of how much air the engine is taking in. Combine pressure, engine displacement, and engine redline, and I'd have a good general idea of how much power the engine is making.

your first analogy doesnt really make sense, i mean it does but in no way does it relate to what im talking about. im talking if you take the exact same engine, and put two different superchargers on it pushing the exact same psi which one is going to flow more air. now pretty much everyone on here says that obviously the larger supercharger will be flowing more air, which seems to make sense if you just take it at that. but psi is the pressure within the intake system, now if your putting more air into the intake system then would it not make sense that there would be more pressure (psi) as the air would be more tightly packed? can someone explain to me how a supercharger can flow more air into the intake system and not as a result produce more pressure within that intake system? can someone post a link or something and point me in the right direction?

ive got a good analgy for this guy. ok lets say you have two ballons. One is a normal sized party Ballon the other is a tiny water ballon. Now you fill each balloon to eactly 4 PSI. Now the smaller balloon occupies much less space than the bigger balloon. So it order to make it reach 4 PSI it doesnt take nearly as much air. Where as the big balloon take sup alot of space, and reaching 4 PSI will take alot more air.

I honestly dont think you know what PSI is, or understand the physics of air volume/air pressure/ and air mass.

The power is, but isn't necessarily made by pressure, as you are talking. But it is the pressure which condenses the molecules which causes better atomization with the fuel, causing more power. You make it sound like the pressure is forcing the piston to move or something, when in reality it is just easier for the flame front to spread quicker when the molecules are closer together. PSI isn't always good, look at detonation!

ive got a good analgy for this guy. ok lets say you have two ballons. One is a normal sized party Ballon the other is a tiny water ballon. Now you fill each balloon to eactly 4 PSI. Now the smaller balloon occupies much less space than the bigger balloon. So it order to make it reach 4 PSI it doesnt take nearly as much air. Where as the big balloon take sup alot of space, and reaching 4 PSI will take alot more air.

I honestly dont think you know what PSI is, or understand the physics of air volume/air pressure/ and air mass.

ok your analogy doesnt really explain much for me either. im talking the same size engine here, 2 different sized superchargers one engine. now the way i read your analogy is that the engine would be the balloon, and filling a smaller balloon (engine) to 4 psi takes less air than filling a big balloon (engine) to 4psi. yes that obviously makes sense. thats not what im talking about though. if thats not the analogy you were trying to make then i have no clue what you are trying to say. i guess you could be saying that the balloons are superchargers? but then youd be pointing out that it takes more air to fill a bigger supercharger to 4psi, but why would you fill a supercharger to 4psi? i appreciate all the replys, i just wish someone had a logical explination that i could understand.

Let me give this a shot

1 engine 3 different blowers and lets say they all hit 15psi of boost.
First is a Centrifugal blower.
Second is a Twin Screw blower.
Third is a Roots blower.


The centrifugal supercharger: The centrifugal supercharger is a fan, that pulls air in and will hit 15 psi at a higher rpms because it uses the rpms to build centrifugal force, which makes the air move from the center of the fan to the outside of the fan blades where it gets scraped and directed thru a small hole into a scroll. The scroll is that tubing that looks like a snail shell. The tubing gets wider as you go further away from the hole, which slows down the air thus creating the pressure aka "the boost". This type of supercharger does not displace any location because it's rotating part does not move into or out of a location that air occupies.


The Twin Screw and Roots blowers are positive displacment superchargers. The rotating mass within each section moves into and out of a area that air will occupy. Before I explain how they work I need to give you few base statements.

Air, just like water and electricity will go where there is the least amount of resistance. If you suddenly create a vacume, air is going to want to fill that vacume. Air also act like or mimick a ball, in that it will follow a curve, and just like a ball, if you have two long screws or twisted wedges that are parallel to each other, but have the threads facing the opposite direction, and you have them spining to the inside of each other, or the outside of each other, the ball will either go down the screws or up the screws, or down the wedges or up the wedges

The twin supercharger: The twin screw supercharger is actually a compressor. The twin screws slices the air that naturally comes in at the inlet when the tips of the twin screw vacate and then occupy the opening of the case. Each time the tips of the screws unblock the opening, it creates a vacume, and that's how the air starts it's path into the supercharger. As the air moves down the pair of screws, it gets squeezed,and that creates the pressure, and thus is pressurized before it gets to the intake.

The Roots Blower: The Roots blower folds air into the intake, and is really the only blower out of the three types of superchargers. The roots design was originally meant to force air down mine shafts. It works by taking air from the top or bottom of a set of blades and moving the air to the opposite side. It has 3 basic twisted wedge shape. Just image two triangles sitting with one edge on the bottom and both triagles attached by three pipes. Now take one triangle and turn it 1/3rd of the way over so that one of the sides is now on the bottom. That's basically what the roots wedges looks like. You have two of those again mirroring each other, so that as the wedge rotates, the air moves diagonally across the case, either from top to bottom or bottom to top. Where ever the air end up at is where the boost is created. FOr a car, that's basically in the intake, and that's where the actuall compression takes place as the air is folded into it. Best example would be your mom's cake mix with it's two blades. As the blades move inward to each other, the batter is pulled in where the blades meet and pushed out where the blades seperate. Where the batter is pulled in is the vacume in a roots blower, and where it is pushed out is where the compression is.


I hope this helps you out. I made it as generalized as possible.

Also the screws are "tighter" or "Closer" to each other than the wedges, so they form a closer seal to each other. The Roots blower does not seal the air as well from the "positive" side to the "negative" and the part of the air that has been folded into the intake gets "recycled" as the wedges rotate. This does not occure with the "Twin screw" superchargers. Also because part of the air is "recycled" that air that is compressed in the intake is warmer than the air drawn in thru the opening of the supercharger. The problem with this is that the warm air will heat up the entire lenght of the wedges as well as the casing. That's why Roots style blowers are not as efficiant as the twin screw blowers.

yes i know all about superchargers, i know what centrifugal, twin screw, and roots blowers are... thats why i have a twin screw =). but none of this answered my question. just so you all know im not a moron, i know an enormous amount about cars, engines, superchargers, volumetric efficiencies, barometric pressure, all that... which is exactly why im asking this question. now since this topic has gotten on a tangent it seems like, i would like to reiterate my original question. an eaton m90 and an eaton m45 are both roots type superchargers, and as the name would imply the m90 is twice the size (flow wise) of the m45. now assuming you took these superchargers and put them on the exact same engine, each one pushing 10psi, would one actually be flowing more air than the other? if the answer to this is yes then explain to me why. i know that every person who reads this will of course say that the m90 is flowing more air, but why! im trying to figure out how it can put more air in the intake system and still be applying the same psi thru that system. am i just looking at this horribly wrong? or does an m45@10psi flow the same amoutn of ar as an m90@10psi? (of course there will be differences in the power output due to volumetric efficincies of each blower, the amount of power it takes to turn them and so on, but just strictly based upon theoretical airflow, will they be the same or different, and if different explain to me why that is)

If you cool your intake charge what happens to the PSI of that charge? Will it stay the same, increase, or drop?

It will drop! But now more volume is now able inter in the same space, so you can increase the volume for the same psi. Get it?

With that increase in volume, you get more power, since there is more air.

The 45 will heat the air more, which has been stated before, so you lose power because the air has expanded. Like I said it has to do with volume, not psi. Psi does not tell you much, unless everything is equal in an engine when dealling with any type of boost powre adders.

Its all about the CFMs baby :iceslolan

ok i think i get your question now. PSI is relavent to the engine size. The bigger the engine, the MORE air and pressure needed to make PSI. The engine can only take in so much air on its own, now PSI as you should know is a measure of force, not mass. But when it comes to engines, the force and the mass are the same thing. Because two of the same engines can only take in so much air at the same time. Which means it will take the exact same amount of air being forced into the engines to make 1 PSI.

Ok now lets forget about efficiency and heat created by the blowers for a minute. Now if you had a M45 and a M90, but them both on the same engine, and set them up to run 10 PSI on both engines, you would be flowing the EXACT same amount of air. Theoretically of course. But the M45 would have to be spinning twice as fast to make the same amount of PSI, but it would still be flowing the exact same amount of air.

So yes, a M45 making 10PSI on one engines moves the exact same amount of air to make 10 PSI than a M90 does to make 10 PSI on the same engine. Only difference is, the m90 does it with only half the speed required of the m45.

ok i think i get your question now. PSI is relavent to the engine size. The bigger the engine, the MORE air and pressure needed to make PSI. The engine can only take in so much air on its own, now PSI as you should know is a measure of force, not mass. But when it comes to engines, the force and the mass are the same thing. Because two of the same engines can only take in so much air at the same time. Which means it will take the exact same amount of air being forced into the engines to make 1 PSI.

Ok now lets forget about efficiency and heat created by the blowers for a minute. Now if you had a M45 and a M90, but them both on the same engine, and set them up to run 10 PSI on both engines, you would be flowing the EXACT same amount of air. Theoretically of course. But the M45 would have to be spinning twice as fast to make the same amount of PSI, but it would still be flowing the exact same amount of air.

So yes, a M45 making 10PSI on one engines moves the exact same amount of air to make 10 PSI than a M90 does to make 10 PSI on the same engine. Only difference is, the m90 does it with only half the speed required of the m45.

No it does not move the same amount of air, the volume is different because of heat, and compressor size!

http://www.automotive.eaton.com/images/products/M90flow.gif

http://www.automotive.eaton.com/images/products/M45flow.gif

Don't look at pressure, look at volume. When you look at superchargers what do the list, psi? Nope! Do they list cfm? Yep! :) I wonder why that is? That's right PSI does not tell you everything. I will say it one last time, VOLUME

Do you get it now? I have just said what boosted did, but with a little different approach.

krisw,

Do you get it, if not re-word your question.

so would jayson be correct in saying that in theory, without taking heat and thermal expansion and whatever into account, the m90 and the m45 would be flowing the exact same amount of air at 10psi?

so would jayson be correct in saying that in theory, without taking heat and thermal expansion and whatever into account, the m90 and the m45 would be flowing the exact same amount of air at 10psi?


Of course not, you still have volume.

Put it this way.

The 45 10psi at 250cfms, would be equal to a 90 at 5psi at 500cfms, roughly.

ive got a good analgy for this guy. ok lets say you have two ballons. One is a normal sized party Ballon the other is a tiny water ballon. Now you fill each balloon to eactly 4 PSI. Now the smaller balloon occupies much less space than the bigger balloon. So it order to make it reach 4 PSI it doesnt take nearly as much air. Where as the big balloon take sup alot of space, and reaching 4 PSI will take alot more air.

I honestly dont think you know what PSI is, or understand the physics of air volume/air pressure/ and air mass.

he should have gotten it by now. I dunno who couldnt understand that. lets just say at a lower rpm boost builds earlier than a smaller supercharger/turbo and will hold longer or gain even more. or would underdrive pulleys give you a feel for work on an engine? oh well i got it.

Let me give this a shot

Now im all confused! lol, i dunno if im baking a cake or building an engine! jk

so would jayson be correct in saying that in theory, without taking heat and thermal expansion and whatever into account, the m90 and the m45 would be flowing the exact same amount of air at 10psi?

The best thing ive ever heard about an engine is that they are all about air flow. The faster air goes in, the faster it comes out, the more power built. air in+air out=more power built. its like putting on a set of heads on a stock motor. they flow a lot more and easier, making more power.

Now im all confused! lol, i dunno if im baking a cake or building an engine! jk

Neither, I thought I was building a house http://www.automotiveforums.com/vbulletin/images/smilies/evil_lol.gif

ok i think im seeing where my problem is, i dont really understand what "psi" is to these manufacturers is. now im assuming that psi is the pressure within an intake manifold, which is what it would be on a car. but when your talking generically, as in not on a specific vehicle, how are they determining when 10psi has been reached?

Write the word Volume.

Imagine psi as the back pressue waiting to get into the cylinders.

PSI is measured at any giving point, it will be the same after the turbo, or supercharger.

ok...i'm not sure if i got this, but as i see it (and i'm praying i'm right) think of that PSI that your pushing is not in the intake, but in the supercharger it's self. The super charge it self is pushing 10 psi of what ever volume that supercharger is (M45, M90, w/e). so in other words, the PSI of boost that is being read, is not the psi in the intake. Now i've never installed a supercharger, or a boost gauge, so i don't know were the sensor will be reading from, so i could just be blowing 30 psi out of my ass. so in other words, yes the M90 will be pushing more at 10 psi. becuase it is all about volume. larger supercharger means higher volume at a lower PSI than a smaller supercharger at the same PSI.

so now for a recap class:
- PSI is how much the supercharger itself is pushing not the amount of pressure in the intake
- a larger volume supercharger would push more air at 10 PSI than the the smaller volume supercharger
- i'm praying i'm right
- i'm hopeing that cleared it up
- i'm not wearing boxers.........

The m90 is gonna make more power at 7psi than the m45 will at 7psi because it takes the bigger supercharger more air to reach the same psi. More air into the motor, therefore making more power.

I think thats right lol.

Write the word Volume.

Imagine psi as the back pressue waiting to get into the cylinders.

PSI is measured at any giving point, it will be the same after the turbo, or supercharger.

that is exactly how i imagine it, psi is the pressure inside the intake/manifold/heads created by the supercharger. thats where my problem lies, to create a certain pressure within the intake system requires a certain amount of air. to make more pressure you would add more air, to make less pressure would require less air. so i dont see how you can have 10psi created by an m45, and 10psi created by an m90 and say that the m90 has pushed more air into the intake than the m45. if there were more air wouldnt there then be more pressure?

You still have not written the word, that is why you do not get it.

P1*V1 = P2*V2

pressure times volume of set up 1 (the 400cfm at 10 psi)
that has to equal the second set up.. (800 cfm at 10psi)

those do not equal so at 5 psi the 2nd set up is gonna have the same flow as the first set up... its basic laws of gases.

if you really want to get techniqual you also need to know the temp of each one so you have:
(p1*v1)/t1) = (p2*v2)/t2

You still have not written the word, that is why you do not get it.

P1*V1 = P2*V2

pressure times volume of set up 1 (the 400cfm at 10 psi)
that has to equal the second set up.. (800 cfm at 10psi)

those do not equal so at 5 psi the 2nd set up is gonna have the same flow as the first set up... its basic laws of gases.

if you really want to get techniqual you also need to know the temp of each one so you have:
(p1*v1)/t1) = (p2*v2)/t2

ok this is where we differ. im thinking of psi as the pressure within the intake manifold, and you seem to be using it as the amount of air the supercharger is flowing. im thinking of 10psi as the constant, no matter whats going on with the size of the supercharger, its going to reach 10psi in the intake manifold. so if your have your m90 running at 5psi, its flowing half the amount as the m45 at 10psi, because its only creating enough pressure within the intake manifold to make 5psi. 5psi is obviously half the psi of 10, so if you have one supercharger creating 5psi within the intake manifold, and hte other supercharger creating 10psi within the intake manifold, 10psi is obviously more. so then what this leads me to believe is that our definitions of psi are different. as i said, im referring to it as the pressure within the intake manifold. you have said that also, however your statement above contradicts this. which is why i have been asking this question in the first place. my definition of psi isnt what is being used when talking about how much superchargers flow.

You forget, what is in the formula? Its that word you have yet to write, and for some reason do not want to understand. Volume is where you start to make your mistake. Volume is part of the equation for a reason. Not just pressure.

Just write it once, forget the pressure being all knowing. Like I have said before psi does not, and will not, and can not tell you the whole story of how boost works. When you learn that, then we will not differ.

Is it a fact that an M90 at the same psi will make more power, yes. Why, because of VOLUME!

Formulas do not lie.

Wow, 3 pages and the guy still can't Understand this?

I thinkI just found where is the problem.

You say when you push more volume of air the pressure will increase in the space between your blower and intake, that's where you are wrong. If air was pushed in a CLOSED AND RIGID space, then yes, as soon as you put more volume in that space, the pressure will rise.

Now in a car, let's imagine pressure can be measured by drilling a hole in the tubing and putting a tube with a disc that goes up as pressure rise and goes down as pressure lowers (that's actually how basic wind meter works)
http://www.northshoreinc.com/Images/NSIWindmeter2.jpg

So, now everyone here tries to tell you that a larger blower will push way more volume for the same pressure.

If you put more volume in the pipe, but the pipe is restricted, then true, the pressure will rise. But, when putting mroe air and keeping the same pressure, it means the air moves faster in your tube. If it was moving at the same speed,then you're right, pressure would rise. I think that when picturing that tube meter you can see what everyone tries to tell you.

So, if you flow a bigger amount of air in the same tube and keep the pressure the same, it means way MORE air (volume) travels into your engine, this makes that you can mix that with more fuel at a good ratio and get way more power.

If you rise pressure, this means the more air (volume) you push travels at a lower speed and thus "pushes" more on the wall of the piping, causing pressure.

Now you understand? I registered on this board only to reply to this (I found this thread while googling on intercoolers)

Etienne

You say when you push more volume of air the pressure will increase in the space between your blower and intake, that's where you are wrong.
Etienne

It will not increase at all? That is what you are saying?

ok someone asked a similar question to this on another board that im on and it was answered in a logical way within a couple posts. as i suspected, the 2 superchargers at 10psi will flow the exact same amount of air (assuming perfect world scenarios aka 100% efficiency and such)

Post what was written, please.

I would like to see how it was worded.

Thanks

Dude just think of it like this,


A pump creates flow not pressure, restrictions in the system creates pressure.

So, your oil pump just moves the oil through the filter and gallies, it's the filter restriction and the oil passeges in your block that create the restriction and cause pressure (PSI, Pounds per Square Inch)


OK, I will use my car for example. the stock heads on a GN will flow in the 190 CFM range (yes they suck horribly.) Well when I had my stock unported heads on the car, it took 26 PSI of pressure to run 11.78. Well If I were to step up to a set of GN-1R's that flow something like 230 CFM, I would get the same results at 21-22 PSI. Now with this stage II on center engine I am building with the Buick stage II heads (340-360 CFM depending on the port job and valve size) I will acheive the same results at like 9-10 PSI.


Sorry to use the GN as an example in the mustang forums, I just know all the flow numbers for the buick stuff
See what I am getting at here? As the airflow restriction was decreased so did the ammount of intake pressure (PSI.) So by seeing that, we can say that BOOST (Measured in PSI) is the mesurement of air you are not using.

Skyline is right, it's all about the CFM's.

ok you didnt read my question... i think we all know by now that if you change your heads you will be able to flow more air... that has absolutely nothing to do with my question.

p.s. here is what was said on the other forum

-Question:This may be a stupid question, but I will throw it out here any way. How does a larger turbo flow more air through the engine at the same pressure? If you have a tube and push air into it slowly until it hits 14PSI it contains a certain volume of air. If you push the air quicker(larger turbo, more cfm) until it hits 14 PSI doesnt it have the same amount of air as pushing air in slower?

-Answer #1: Bigger turbos make more power not because of CFM (cubic feet/minute), but because of greater efficiency. A larger turbo has a larger turbine section, which doesn't restrict exhaust as much as a smaller turbine. The compressor section of a larger turbo also is more efficient at higher flow than a small turbo, which means the compressed air is heated less and is therefore more dense at X psi. Larger turbos are rated at a higher CFM because they are able to operate efficiently at these flow rates.

How much CFM = PSI is determined by how the whole system flows... intake, head, intake manifold, exhaust, etc. Turbos create pressure because they try to push more air into the engine than the engine wants. The air backs up and becomes pressurized. The more flow you try to feed it, the higher the pressure.

To use the garden hose example, imagine if you had a fire hydrant and a regular faucet. The fire hydrant is able to flow a whole lot more, but if you hook a garden hose up to it that hose is going to be under much greater pressure from the increased flow. Same deal if you put a fire hose on a garden faucet; the same water that made a great spray from the garden hose comes out of a fire hose as a trickle

-Answer #2: you can push different pressure at the same CFM or = CMF and different PSI. But the problem poeple have is that all our Intake manifolds are the same, so how does 7psi from two turbos which ends up in the same garden hose make more power?

The answer lies in the density, temps, efficency and the tuning flexability it allows.

SO THE QUESTION HAS PRETTY MUCH BEEN ANSWERED BUT I WANTED TO MAKE 100% SURE SO I ASK: ok so then in a perfect world where everything was 100% efficient, two different sized turbos creating 10psi within two identical intake manifolds would be pushing the same amount of air?

-Answer to my question: Yep, assuming the temperature of the air is the same

SO THE QUESTION HAS PRETTY MUCH BEEN ANSWERED BUT I WANTED TO MAKE 100% SURE SO I ASK: ok so then in a perfect world where everything was 100% efficient, two different sized turbos creating 10psi within two identical intake manifolds would be pushing the same amount of air?

-Answer to my question: Yep, assuming the temperature of the air is the same


Wrong!

It would be impossible to achieve that!

ok now your just arguing the wrong things. obviously its physically impossible to achieve 100% efficiency, im not trying to find a supercharger that will do that. im just saying that assuming 100% efficiency they would flow the same amoutn of air.

ok now your just arguing the wrong things. obviously its physically impossible to achieve 100% efficiency, im not trying to find a supercharger that will do that. im just saying that assuming 100% efficiency they would flow the same amoutn of air.


Ok look dude, since you obviously refuse to listen and understand go buy a little blower and then a bigger blower. Put them on the same car and dyno the car each time. Obviously according to you nobody here knows a damn thing so go out and waist the money to prove to yourself that some people here where not born with their head up their ass.

This thread should be closed...

ok now your just arguing the wrong things. obviously its physically impossible to achieve 100% efficiency, im not trying to find a supercharger that will do that. im just saying that assuming 100% efficiency they would flow the same amoutn of air.


No, that is not my point.

I see how you are trying to look at it, but its not the right way.

If two different blowers are 100% efficient, and both are blowing 10psi in the same intake, are they at the same RPM? Where in the rev range do they make 10psi, at the same point, with same volume, if that is the case they are the same blower, and not of different sizes that your mind is so wrapped up on. That is my point.

You want the laws of physics to agree with what you are saying, in that aspect you are making a mockery of physics?

No, that is not my point.

I see how you are trying to look at it, but its not the right way.

If two different blowers are 100% efficient, and both are blowing 10psi in the same intake, are they at the same RPM? Where in the rev range do they make 10psi, at the same point, with same volume, if that is the case they are the same blower, and not of different sizes that your mind is so wrapped up on. That is my point.

You want the laws of physics to agree with what you are saying, in that aspect you are making a mockery of physics?

it just doesnt seem possible to me. explain to me how you can create the same pressure within 2 intakes and have more air in one than the other?

man, are you laughing at us or you really don't WANT to understand?

we've explained you 438732 times how it work and you seem to be so sure that we're all untrue that you even go ask on other forum until you find one where one person will say as you and then you think you are right?

Take another analogy. Make it a river 30ft wide. Somewhere in the river, it goes to 15ft wide. The depth is always the same.

Now, on that same river, you can have a good flow (for water, it's cubic feet of water per second) and that restriction of 15ft will create the backpressure.

Now, on the same iver, you could flow twice the amount of water (ft³/sec) and still get the same level (the water level won't increase, just the current will be stringer) and the same backpressure. The water will only flow way faster from the start to the end of the river, but the level will stay the same.

In a river there can be very strong current or almost no current and the level still the same, the backpressure created by the 15ft place will be the same.

Now for more mods, you can dig that 15ft to make it 25ft, you will then be able to flow even more water before getting at the max capacity of that river.

Come on, this thread should be closed, I'm sure we can show you srawings, everything, but still you will be sure that we are not right and you are. Then why ask the question if you don't want the real anwser?

I know a guy who took out his supercharger on his C230 kompressor, then he changed it for a Turbo. The SC was at 11psi and pushing 160whp, now the turbo is not even at 9psi and pushing 268whp. See, if both units were at 10psi, the turbo would flow way MORE air into the car but at the same backpressure.

If I continue, my next reply will need teletubbies for you to understand

Etienne

it just doesnt seem possible to me. explain to me how you can create the same pressure within 2 intakes and have more air in one than the other?

I have written it over and over again, along with some other guys.

I don't think locking this thread is enough, just delete it. It should be erased from existance, anyone who ever mentions it again should be bludgeoned. Everytime I see 'Response to post "boost question" in my inbox I want to beat my head against my desk.

No, there is some good info in here for some of the newer guys

No, there is some good info in here for some of the newer guys

Ya this thread has really helped me understand more about boost and how it works. Thanks guys to those of you who made helpfull replys.

I was thinking about closing it a while ago but I figured at some point the original questioner would understand.... maybe I was wrong but I'll leave it be for now.

hmmm...i htink he's just looking at pressure wrong (this is just how i view it, and it makes sense to me, but maybe this is what they've been saying all along).

Pressure is techinically, in a sense the same as density, except it's not one solid material, but a gass with in a solid container. so if you have a a container that's volume is 130 cm3, (say 1g = 1 cm3) and you put 260g of gas in there, because of gas's properties, it's giong to squish up and compress, which is pressure. now that is just in basic phsyics clas (please correct if i'm wrong here)

now..when talking about super charges, i tend to look at PSI as more of an indirect measurement of flow. the s/c has a 130 cm3 volume (for exapmle of course) the faster the fan spins the more mass will be introduced into that volume there for creating more pressure. now when a gas compresses it has a tendency to want to expand, which it can't really do, so it heads as quickly as it can (or at a velocity proportional to the need to expand from the compressed air) for the area with the less resitance, which would be the exhaust port of the s/c (as in the hole that connects to the manifold). Now, this also means (in concern with the volume) the larger the volume the more mass needed to create a certain amount of pressure. now i'm sorry if this seems it's all just being slapped together, which it is, so if one of the wiser ones wishes to fix this go ahead. SO, if you want you're larger s/c to achieve, say, 5 psi it needs more mass of gas, or volume that's the word the rest of you hvae used for it so after this i'll stick with that, in order to achieve that (dur), which means it will be pushing more air at 5 PSI than the smaller volume s/c would be pushin at 5 PSI.

ADD CORRECT AND REARRANGE AS YOU WISH, but stop with the uber techincal, and mathematical parts, make it sweet and blunt, like you're explainging it to a 13 year old, less confusin that way

Ya this thread has really helped me understand more about boost and how it works. Thanks guys to those of you who made helpfull replys.

If he doesnt understand now, he wont ever. Besides, i think hes out of excuses of why he doesnt understand now.

but the amount of air a supercharger flows and the pressure within the intake manifold are directly related to one another.

This is where I believe you are going wrong. The amount of air a supercharger flows and the pressure within the intake manifold are inversely related to one another. Notice in the charts posted earlier in this thread that the air flow at 5 psi is greater than the airflow at 10 psi. The pressure in the intake is going to resist the movement additional air into the intake from the s/c. To move air, you need a difference in pressure between two points, and the bigger difference results in more flow. The more powerful the s/c, the bigger pressure difference it creates. A large s/c will create more power than a small s/c at identical rpms. For instance, a large fan has more blade area and the tips of each arm are moving at a greater linear speed. Also, the pressure in the s/c will not be the same as the pressure at the intake because each volume has different characteristics.

Would everyone else agree with this?

By the way, MrSpace, if you want to add air to a container and keep the same pressure, are you sure you wouldn't want to lower the temperature and slow the molecules down?

This is where I believe you are going wrong. The amount of air a supercharger flows and the pressure within the intake manifold are inversely related to one another. Notice in the charts posted earlier in this thread that the air flow at 5 psi is greater than the airflow at 10 psi. The pressure in the intake is going to resist the movement additional air into the intake from the s/c. To move air, you need a difference in pressure between two points, and the bigger difference results in more flow. The more powerful the s/c, the bigger pressure difference it creates. A large s/c will create more power than a small s/c at identical rpms. For instance, a large fan has more blade area and the tips of each arm are moving at a greater linear speed. Also, the pressure in the s/c will not be the same as the pressure at the intake because each volume has different characteristics.

Would everyone else agree with this?

By the way, MrSpace, if you want to add air to a container and keep the same pressure, are you sure you wouldn't want to lower the temperature and slow the molecules down?


100% Right on man. Good way of looking at it.

that's why there is an ontercooler, to further pack more air into the same area and pressure.

PV = nRT where T = temperature.. simple equation.
if you keep pressure and volume constant and pack mre air, then you lower the temperature!

basic physics :)