boost question

[krisw]

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?

[SkylineUSA]

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.

[breaknstuf4fun]

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.........

[351wStang]

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.

[krisw]

Originally Posted by SkylineUSA

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?

[SkylineUSA]

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

[krisw]

Originally Posted by SkylineUSA

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.

[SkylineUSA]

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.

[MrSpace]

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)


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

[SkylineUSA]

Originally Posted by MrSpace

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?

[krisw]

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)

[SkylineUSA]

Post what was written, please.

I would like to see how it was worded.

Thanks

[Hypsi87]

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.

[krisw]

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

[SkylineUSA]

Originally Posted by krisw

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!