Something i never fully understood about these cars...

[AB18]

Is the way we calculate boost. Our boost guages read 18psi ish on a normal stage 2+ S4. Obviously each turbo doesn't make 18psi for a total of 36psi. Does anyone have a more in depth explanation?

[Chknkatsu]

boost isn't like water, 1 gallon + 1 gallon = 2 gallon

the pressure made by the turbos build up a pressure of X amount of PSI

a twin turbo car won't make 2 times the pressure

like having 2 TVs on with the volume on the same level...it doesn't get any louder

[Boris]

boost isn't like water, 1 gallon + 1 gallon = 2 gallon

the pressure made by the turbos build up a pressure of X amount of PSI

a twin turbo car won't make 2 times the pressure

like having 2 TVs on with the volume on the same level...it doesn't get any louder

Chicken Katsu..come here let me eat a piece of you leg...

[RenegadeEngr]

biturbo = 1 turbo per bank....twin turbo might of made you think that way...

[obviouspro]

boost isn't like water, 1 gallon + 1 gallon = 2 gallon

the pressure made by the turbos build up a pressure of X amount of PSI

a twin turbo car won't make 2 times the pressure

like having 2 TVs on with the volume on the same level...it doesn't get any louder

That is a great analogy. It's been a while since I've taken physics. But like you said you can't just simply add pressure. What I think, please correct me if I am wrong, is that with two turbos there is the same pressure(18 psi) just twice as much air being moved.
Haha Boris your comment made me laugh.

[Boris]

That is a great analogy. It's been a while since I've taken physics. But like you said you can't just simply add pressure. What I think, please correct me if I am wrong, is that with two turbos there is the same pressure(18 psi) just twice as much air being moved.
Haha Boris your comment made me laugh.

Yes I am really hungry, and If his leg regenerated Im sure he would oblige, or if he didn't. I would hold him down and eat his leg anyways, knowing that it would grow back.

As to the italicized part of your comment, I was schooled on this extensively a few months ago during this debate on here.

I always thought it was twice as much air also! But apparently it is not, it is just 18 PSI of air, which is 18 psi of air...It might be cooler, or hotter, which would change its density I guess, but the actual amount of air is still 18 psi coming into the intake mani.

so when you read 18 psi, thats how much boost is being created and the pressure coming into the intake mani...no more than that.

[obviouspro]

Yes I am really hungry, and If his leg regenerated Im sure he would oblige, or if he didn't. I would hold him down and eat his leg anyways, knowing that it would grow back.

As to the italicized part of your comment, I was schooled on this extensively a few months ago during this debate on here.

I always thought it was twice as much air also! But apparently it is not, it is just 18 PSI of air, which is 18 psi of air...It might be cooler, or hotter, which would change its density I guess, but the actual amount of air is still 18 psi coming into the intake mani.

so when you read 18 psi, thats how much boost is being created and the pressure coming into the intake mani...no more than that.

Than why have two turbos? Not trying to be a jerk haha, serious question.

[Chknkatsu]

That is a great analogy. It's been a while since I've taken physics. But like you said you can't just simply add pressure. What I think, please correct me if I am wrong, is that with two turbos there is the same pressure(18 psi) just twice as much air being moved.
Haha Boris your comment made me laugh.

yup, that's the way I see it. the turbos together move Xvolume of air. the pressure/density? of X is Ypsi

...I'm too tired for this

[Chknkatsu]

and no you can't eat my leg :runs away:

[RogueStatus]

like having 2 TVs on with the volume on the same level...it doesn't get any louder

wouldnt that be louder? say 2 speakers per tv (using 2 for an example),so 2 speakers per tv,both at the same volume,equals 4 speakers pushing the same volume...4 speakers would be louder than 2, no?

[Chknkatsu]

I just tested my theory with my ipod on a 3rd party speaker and my computer playing the exact same soong synced together, and it's actually not louder (by ear). yes the sound is more surrounded, but the decipal remains the same. I know it's a irrelevant test since theres no real proof, but I think it's a valid analogy

[Chknkatsu]

http://ergo.human.cornell.edu/studen...coustics1.html

i guess I'm kind of wrong, but right at the same time

Combined Effects of Sound

Because the decibel scale is logarithmic rather than arithmetic, a large increase in sound power will be reflected in a change of only a few decibels. For example:

* one TV set operates at 65 dB
* two TV sets, at 65 dB each = 68 dB
* ten TV sets, at 65 dB each = 75 dB

To estimate what the combined noise will be from combined two noise sources you can calculate the difference in noise level between any two noise sources. If the difference is 0 or 1 dB add 3dB to the louder of the 2 noise sources; if it's 2 or 3 add 2 dB to the louder; if it's 4-10 add 1 dB to the louder, and if it's 11 or more then there's no impact on the louder noise.

[RogueStatus]

haha so i was right? i was just guessing because it seemed logical. i wasnt turning this into another AZ argument thread

good research bill nye. haha.

[Chknkatsu]

haha so i was right? i was just guessing because it seemed logical. i wasnt turning this into another AZ argument thread

good research bill nye. haha.

well I wasn't sure by how much louder you would think it would be, some people would think two sources would mean two times more. but I was close ;) Touche'

[infinkc]

can you run a single turbo on the car using only one exhaust side?

[Audi S4 Turbo]

Correct. Also think of it this way, you are at a sports stadium. Your team wins and everyone claps together. It gets pretty loud. This does not mean an individual can clap louder than you, but when you have thousands of people, it can get loud.

Pretty cool stuff.

http://ergo.human.cornell.edu/studen...coustics1.html

i guess I'm kind of wrong, but right at the same time

Combined Effects of Sound

Because the decibel scale is logarithmic rather than arithmetic, a large increase in sound power will be reflected in a change of only a few decibels. For example:

* one TV set operates at 65 dB
* two TV sets, at 65 dB each = 68 dB
* ten TV sets, at 65 dB each = 75 dB

To estimate what the combined noise will be from combined two noise sources you can calculate the difference in noise level between any two noise sources. If the difference is 0 or 1 dB add 3dB to the louder of the 2 noise sources; if it's 2 or 3 add 2 dB to the louder; if it's 4-10 add 1 dB to the louder, and if it's 11 or more then there's no impact on the louder noise.

[stussy]

can you run a single turbo on the car using only one exhaust side?

ain't a whole lot of space under the hood. plus, you're looking at lag with bigger turbos.

[jaredsogn]

Actually, it does mean it is twice as loud. You guys do realize that an increase of 3db is doubling the amplitude right? So from 65db to 68db is twice as loud.

well I wasn't sure by how much louder you would think it would be, some people would think two sources would mean two times more. but I was close ;) Touche'

[RogueStatus]

Actually, it does mean it is twice as loud. You guys do realize that an increase of 3db is doubling the amplitude right? So from 65db to 68db is twice as loud.

increasing 3db is doubling? i dont have a clue,i was simply going by experience (having 2 football games on at once) and it was louder,but they were 2 different TVs with different speaker setups and whatnot...but i dont know,its 4AM,im at work,and its not the topic in question,so if you know for a fact,thanks for the clarification

i also had 118db horns in my STi,and so did my friend,and i know when they were next to each other with all horns going,it was not only annoyingly loud,but louder than it would be with just one.

[jibberjive]

http://ergo.human.cornell.edu/studen...coustics1.html

i guess I'm kind of wrong, but right at the same time

Combined Effects of Sound

Because the decibel scale is logarithmic rather than arithmetic, a large increase in sound power will be reflected in a change of only a few decibels. For example:

* one TV set operates at 65 dB
* two TV sets, at 65 dB each = 68 dB
* ten TV sets, at 65 dB each = 75 dB

To estimate what the combined noise will be from combined two noise sources you can calculate the difference in noise level between any two noise sources. If the difference is 0 or 1 dB add 3dB to the louder of the 2 noise sources; if it's 2 or 3 add 2 dB to the louder; if it's 4-10 add 1 dB to the louder, and if it's 11 or more then there's no impact on the louder noise.

Funny how this thread got sidetracked.

Double the cone area (ie. 4 of the same speakers compared to 2, assuming they all maintained the same power input) and you'll theoretically gain 3db. So
*1 TV set = 65db
*2 TV sets = 68db
*4 TV sets = 71db
etc.

However it's generally accepted that 10 db is doubling the "perceived" loudness, and a change of ~3db is the minimum increment that the human ear can perceive change in loudness.

[Grangalan]

Aye...theres still only 18 psi being made, but the amount of air being crammed into the engine is more than a single k03/4 would make. Same pressure but more of it. PSI does not equal CFM,

[sCeRaXn]

Yes I am really hungry, and If his leg regenerated Im sure he would oblige, or if he didn't. I would hold him down and eat his leg anyways, knowing that it would grow back.

As to the italicized part of your comment, I was schooled on this extensively a few months ago during this debate on here.

I always thought it was twice as much air also! But apparently it is not, it is just 18 PSI of air, which is 18 psi of air...It might be cooler, or hotter, which would change its density I guess, but the actual amount of air is still 18 psi coming into the intake mani.

so when you read 18 psi, thats how much boost is being created and the pressure coming into the intake mani...no more than that.

Thats not true at all. The pressure created by both turbos will be equal...adding 18psi of gas to 18psi of gas yields 18psi of gas(air in this case) lol. The difference is airflow in cfm. The airflow will effectively double even though the pressure stays the same. This is why two turbos working exactly the same will make more power than a single turbo of the same kind. Its also why a larger turbo will make more power at the same boost level as a smaller one...the airlfow increases.

Also, if the density of air changes, then the boost pressure changes. If the air is super heated and only makes 16psi instead of the requested 18psi, then there is still only 16psi of pressure. You wont see 18psi on the boost gauge if there is only 16psi being created in the IM. What you see on the boost gauge is what your manifold is experiencing(considering your boost gauge is accurate).

[GramCracker]

LOL. This thread is awesome. Derailed, but in the coolest/smartest way possible.

I love it.

[jaredsogn]

Wrong in so many ways. Here is my opinion from a chemistry based background. Most of this can be simply explained with the Ideal Gas Law, PV=nRT. 18psi + 18psi is not 18psi. In fact, you cannot add to "pressures" together into a container, unless both were in the same size container. Theoretically, in a static volume container, doubling the amount of gas doubles the pressure. Therefore, if you added two equal volumes of gas at equal pressure together, like 18psi + 18psi, you should result with a pressure of 36psi. Pressure is not what matters anyways, it is the amount of air you can cram into the cylinders. The amount of boost pressure we see is simply a product of how much air can be packed into the cylinder before the valves close. Also, you can see that as temperature increases, the pressure will also increase. In our case, since the turbos are regulated by boost pressure and not amount of air, we can assume that P and V will stay constant. Increasing Temperature, T, will in turn cause the number of moles of oxygen, n, to decrease, which explains why as intake temperature rises, the boost stays the same but the amount of air flow into the engine decreases. Therefore, you will typically not see the boost pressure drop from 18 to 16, but rather the amount of air molecules going into the intake will decrease, because it is less dense when heated.

Thats not true at all. The pressure created by both turbos will be equal...adding 18psi of gas to 18psi of gas yields 18psi of gas(air in this case) lol. The difference is airflow in cfm. The airflow will effectively double even though the pressure stays the same. This is why two turbos working exactly the same will make more power than a single turbo of the same kind. Its also why a larger turbo will make more power at the same boost level as a smaller one...the airlfow increases.

Also, if the density of air changes, then the boost pressure changes. If the air is super heated and only makes 16psi instead of the requested 18psi, then there is still only 16psi of pressure. You wont see 18psi on the boost gauge if there is only 16psi being created in the IM. What you see on the boost gauge is what your manifold is experiencing(considering your boost gauge is accurate).

[RogueStatus]

[J-tec]

My gahd the analogizes flying around here and getting corrected, then recorrected LOL

[AudiA4_20T]

Dalton's Law of Partial Pressures

Dalton's law of partial pressures states that the total pressure of a mixture of gases equals the sum of the pressures that each gas would exert if it was present alone. The pressure exerted by one gas in a mixture of gases is the partial pressure of that individual gas. This law assumes that the gases do not react with each other, but that each gas is a separate component of the system.

Dalton's law of partial pressures can be mathematically expressed by the following. If Pt is the total pressure of a mixture of gases and P1, P2, etc. are the pressures that each gaseous component would exert by itself, then the total pressure is given by Pt = P1 + P2 + etc. Dalton's law of partial pressures tells us that each gas behaves independently of the other gases in the mixture, i.e., each exerts its own pressure (the partial pressure) providing the gases do not react.

Cliff Notes: The total pressure of a mixture of gases (air from each turbo) = the sum of the pressures that each gas (air forced by each turbo in this case) would exert if it was present alone

/thread

[sCeRaXn]

Wrong in so many ways. Here is my opinion from a chemistry based background. Most of this can be simply explained with the Ideal Gas Law, PV=nRT. 18psi + 18psi is not 18psi. In fact, you cannot add to "pressures" together into a container, unless both were in the same size container. Theoretically, in a static volume container, doubling the amount of gas doubles the pressure. Therefore, if you added two equal volumes of gas at equal pressure together, like 18psi + 18psi, you should result with a pressure of 36psi. Pressure is not what matters anyways, it is the amount of air you can cram into the cylinders. The amount of boost pressure we see is simply a product of how much air can be packed into the cylinder before the valves close. Also, you can see that as temperature increases, the pressure will also increase. In our case, since the turbos are regulated by boost pressure and not amount of air, we can assume that P and V will stay constant. Increasing Temperature, T, will in turn cause the number of moles of oxygen, n, to decrease, which explains why as intake temperature rises, the boost stays the same but the amount of air flow into the engine decreases. Therefore, you will typically not see the boost pressure drop from 18 to 16, but rather the amount of air molecules going into the intake will decrease, because it is less dense when heated.

Wow that was a long response for nothing. Im sorry, but adding 18psi to 18psi in a DYNAMIC container(an engine in this case) will never...and i repeat...NEVER equal 36psi. Its physically impossible. Youve got to remember, compressed gas may act like a liquid while in motion(thus the term fluid dynamics), but they differ greatly as to how the respond to pressure. If we were talking about liquid you would be correct, but as far as compressed air is concerned you are way off. Molecules in compressed air can work independently of eachother without a single reaction, which allows them to co-exist while sustaining the same pressure as they would have on their own. I really suck at explaining things like this, but i hope its made atleast a little bit of sense lol.

There are atleast 500 different laws/theories that prove this. If youre like me and refuse to take everything you read online as a definite proof, then id highly suggest picking up Physical Fluid Dynamics by DJ Tritton. It is by far the best book on FD's theories and principles, and MANY other corresponding theories...and unlike many textbooks its laid out in a way that anyone with a HS education can understand. Ive used this book to help design everything from extremely long tube headers for a 760hp 7l LS series Comp. Sand Rail, to port designs for various heads. Its definitely a great read!

[csre9]

I've learned more from this thread than I have in my Physics class im sitting in all year.
I love AZ.

[Don Supreme]

Dalton's Law of Partial Pressures

Dalton's law of partial pressures states that the total pressure of a mixture of gases equals the sum of the pressures that each gas would exert if it was present alone. The pressure exerted by one gas in a mixture of gases is the partial pressure of that individual gas. This law assumes that the gases do not react with each other, but that each gas is a separate component of the system.

Dalton's law of partial pressures can be mathematically expressed by the following. If Pt is the total pressure of a mixture of gases and P1, P2, etc. are the pressures that each gaseous component would exert by itself, then the total pressure is given by Pt = P1 + P2 + etc. Dalton's law of partial pressures tells us that each gas behaves independently of the other gases in the mixture, i.e., each exerts its own pressure (the partial pressure) providing the gases do not react.

Cliff Notes: The total pressure of a mixture of gases (air from each turbo) = the sum of the pressures that each gas (air forced by each turbo in this case) would exert if it was present alone

/thread

Go Clint!!!

[jibberjive]

Do you guys think that 2.8 heads (on 2.7 cams with stock intake mani) would be a more beneficial upgrade than a upgraded intake mani on stock 2.7 heads?

[98a4]