The theory of boost?

[GorGasm]

The subbie sequential is a sack of shit. 4 psi at 4krpm and 13 psi at 7, coupled with a 8.5 CR and you get a pig.

[Si]

difference in the systems is AFAIK is the subbie uses two different sized turbos (vf8 and vf10?)

vs the supra and rx7 using same sized turbos but set up sequentialy......

[SUBARUCONVERT]

The subaru uses a same sizied turbo setup, abilt with a silghtly differnt A/R on the exhuast housing. The older ones arnt that quick, but the GTB versions are. the power isnt smooth but i think people are strechin the story with no power from 4-5K and only 4psi boost. everyone i have driven the VOD lasts about 500 rpm. they make max torque at 5k so that really doesnt sound rite. They pull well all the way to 7.5 or 8k depending on model unlike some other TT's (cough VR-4)

[CozmoNz]

Quite interesting when you see the setup without the engine in there , very cool..

wastegate.. no wastegate... what the hell!

[Dell'Orto]

. the power isnt smooth but i think people are strechin the story with no power from 4-5K and only 4psi boost. everyone i have driven the VOD lasts about 500 rpm.

Nup, the one I drove (I'd just put a boost gauge into) dropped right back to 1-2psi at 4k, then jumped back up to 7 at 5...completely stock standard car though, with a decent intake and exhaust it might be better.

[SUBARUCONVERT]

sounds like theres somthing wrong with it, the boost shouldnt drop any lower than 5 psi during VOD, and once the second turbo is spooled boost should reach 10 psi or more regaurdless of model

[neon_spork]

Time for an engineer to shed some light on the fluids side of things...

The mass flow rate will be the same at any point. kg/second

You are talking about volume flow rate (cfm) or in proper units, m^3/second. and Pressures (bar or psi) or in SI units kPa.

If you treat air as an idea gas (which should be pretty accurate) then the relationship is Pv = RT

P = pressure in kPa,
v = specific volume (Volume/Mass)
R = Gass constant for air
T = temperature in Kelvin

Volume flow rate is equal to the area x velocity (m^2 x m/s = m^3/s) Area of the inlet and velocity of the air can be measured.

Mass flow rate is equal to the volume flow rate x density (m^3/s x kg/m^3 = kg/s)
Inlet temperature can be measured, pressue at this point is known to be 1atmosphere or 101.3 kPa and from these density can be calculated or taken from a table.

specific volume = 1 over mass flow rate x volume flow rate (s/kg * m^3/s = m^3/kg)

So if you know ur volume flow rate and you mass flow rate at a point you can get the specifi volume (v). Then using the Idea gas equation you can find the pressure.

Pressure = R.T/v

R(gas constant) for air is 0.286 kJ/kg.K
T(temp in K) = deg C + 273

Hope that helps

[Stealer Of Souls]

Time for an engineer to shed some light on the fluids side of things...

The mass flow rate will be the same at any point. kg/second

You are talking about volume flow rate (cfm) or in proper units, m^3/second. and Pressures (bar or psi) or in SI units kPa.

If you treat air as an idea gas (which should be pretty accurate) then the relationship is Pv = RT

P = pressure in kPa,
v = specific volume (Volume/Mass)
R = Gass constant for air
T = temperature in Kelvin

Volume flow rate is equal to the area x velocity (m^2 x m/s = m^3/s) Area of the inlet and velocity of the air can be measured.

Mass flow rate is equal to the volume flow rate x density (m^3/s x kg/m^3 = kg/s)
Inlet temperature can be measured, pressue at this point is known to be 1atmosphere or 101.3 kPa and from these density can be calculated or taken from a table.

specific volume = 1 over mass flow rate x volume flow rate (s/kg * m^3/s = m^3/kg)

So if you know ur volume flow rate and you mass flow rate at a point you can get the specifi volume (v). Then using the Idea gas equation you can find the pressure.

Pressure = R.T/v

R(gas constant) for air is 0.286 kJ/kg.K
T(temp in K) = deg C + 273

Hope that helps

What happened to the n (number of mols) in the gas equation?

Anyways. Too much math. More general please.
I am an engineer. Just not a fluids person. It's all getting so technical.

No, it's not a linear relationship. Theorectically New Flow Rate = Old Flow Rate x the square root of (New Pressure divided by Old Pressure), but that may not be what happens in real life as the infernal combustion engine is a bit more complicated than the usual "pressure vs flow" model.

Okay cool. But my general thinking is correct. Complex physics aside. With roughly twice the flow (2x160CFM), I would end up with around about twice the pressure (2BAR absolute). Give or take a number of factors.


Pv=nrT
assuming v, r, and T are constant (of course they wouldn't be... but for arguments sake).
P doubles, n doubles.
yeah?

[Ako]

The subaru uses a same sizied turbo setup, abilt with a silghtly differnt A/R on the exhuast housing. The older ones arnt that quick, but the GTB versions are. the power isnt smooth but i think people are strechin the story with no power from 4-5K and only 4psi boost. everyone i have driven the VOD lasts about 500 rpm. they make max torque at 5k so that really doesnt sound rite. They pull well all the way to 7.5 or 8k depending on model unlike some other TT's (cough VR-4)

I love debunking this particular argument.

My TT VR4's all made power up to the 8200 limiter, with f-all of the boost a subby needed to make the same. The TT subbys have a reputation for being awesome at overtaking - the reason for that is the fact they suck at everything else, so the owners all push the one thing the cars good at


Simultaneous = win

[fivebob]

If you treat air as an idea gas (which should be pretty accurate) then the relationship is Pv = RT

P = pressure in kPa,
v = specific volume (Volume/Mass)
R = Gass constant for air
T = temperature in Kelvin

What happened to the n (number of mols) in the gas equation?

I think you will find that it's taken into account by using the specific volume which appears to be calculated as Volume/Mass, but I'm not an Engineer and the wording above is somewhat confusing to my poor wee uneducated mind

No, it's not a linear relationship. Theorectically New Flow Rate = Old Flow Rate x the square root of (New Pressure divided by Old Pressure), but that may not be what happens in real life as the infernal combustion engine is a bit more complicated than the usual "pressure vs flow" model.

Okay cool. But my general thinking is correct. Complex physics aside. With roughly twice the flow (2x160CFM), I would end up with around about twice the pressure (2BAR absolute). Give or take a number of factors.


Pv=nrT
assuming v, r, and T are constant (of course they wouldn't be... but for arguments sake).
P doubles, n doubles.
yeah?

No, from the equation I gave you need 4 times the flow for double the pressure, double pressure would only give 1.4 times the flow.

[CozmoNz]

The subaru uses a same sizied turbo setup, abilt with a silghtly differnt A/R on the exhuast housing. The older ones arnt that quick, but the GTB versions are. the power isnt smooth but i think people are strechin the story with no power from 4-5K and only 4psi boost. everyone i have driven the VOD lasts about 500 rpm. they make max torque at 5k so that really doesnt sound rite. They pull well all the way to 7.5 or 8k depending on model unlike some other TT's (cough VR-4)

I love debunking this particular argument.

My TT VR4's all made power up to the 8200 limiter, with f-all of the boost a subby needed to make the same. The TT subbys have a reputation for being awesome at overtaking - the reason for that is the fact they suck at everything else, so the owners all push the one thing the cars good at


Simultaneous = win

they have said it alot in this thread, its not pressure, its flow thats important...

what, 20psi on a ct9 is the same as 20psi on a ct20b? no.... excactly

[Punter]

they have said it alot in this thread, its not pressure, its flow thats important...

what, 20psi on a ct9 is the same as 20psi on a ct20b? no.... excactly

If you assume that the charge temp is the same, and its on the same motor with no other changes. Then yes thats exactally the same.

Although i'm sure in real life the exhaust housing on a ct9 would choke it up.

[Ako]

Cozmo what are you on about?

[fivebob]

they have said it alot in this thread, its not pressure, its flow thats important...

what, 20psi on a ct9 is the same as 20psi on a ct20b? no.... excactly

If you assume that the charge temp is the same, and its on the same motor with no other changes. Then yes thats exactally the same.

No it's not. The CT-9 will have more restriction in the turbine so the flow will be less. How many times do I have to say it;
Boost pressure is caused by restriction in the system, flow makes the HP, not boost

Although i'm sure in real life the exhaust housing on a ct9 would choke it up.

If you knew that then why contradict yourself by saying they are the same.

[fivebob]

Cozmo what are you on about?

For once Cozmo is making sense and the rest of you are missing this momentous event

[Punter]

they have said it alot in this thread, its not pressure, its flow thats important...

what, 20psi on a ct9 is the same as 20psi on a ct20b? no.... excactly

If you assume that the charge temp is the same, and its on the same motor with no other changes. Then yes thats exactally the same.

No it's not. The CT-9 will have more restriction in the turbine so the flow will be less. How many times do I have to say it;
Boost pressure is caused by restriction in the system, flow makes the HP, not boost

Although i'm sure in real life the exhaust housing on a ct9 would choke it up.

If you knew that then why contradict yourself by saying they are the same.

Yea sorry that was badly worded , you now what i mean

[CozmoNz]

Cozmo what are you on about?

For once Cozmo is making sense and the rest of you are missing this momentous event

quoted, notepadded, and saved, this is a rare event.

[neon_spork]

If you treat air as an idea gas (which should be pretty accurate) then the relationship is Pv = RT

P = pressure in kPa,
v = specific volume (Volume/Mass)
R = Gass constant for air
T = temperature in Kelvin

What happened to the n (number of mols) in the gas equation?

I think you will find that it's taken into account by using the specific volume which appears to be calculated as Volume/Mass, but I'm not an Engineer and the wording above is somewhat confusing to my poor wee uneducated mind

Yeah your right, The equation P.V = n.Ru.T when V is volume and n is number of mols and Ru is the universal gas constant goes to P.v = R.T when you substitute specific volume v and the gas constant for a certain gas R.

[Stealer Of Souls]

Yeah your right, The equation P.V = n.Ru.T when V is volume and n is number of mols and Ru is the universal gas constant goes to P.v = R.T when you substitute specific volume v and the gas constant for a certain gas R.

Are we okay to assume that V does not change in this instance?

[SUBARUCONVERT]

The subaru uses a same sizied turbo setup, abilt with a silghtly differnt A/R on the exhuast housing. The older ones arnt that quick, but the GTB versions are. the power isnt smooth but i think people are strechin the story with no power from 4-5K and only 4psi boost. everyone i have driven the VOD lasts about 500 rpm. they make max torque at 5k so that really doesnt sound rite. They pull well all the way to 7.5 or 8k depending on model unlike some other TT's (cough VR-4)

I love debunking this particular argument.

My TT VR4's all made power up to the 8200 limiter, with f-all of the boost a subby needed to make the same. The TT subbys have a reputation for being awesome at overtaking - the reason for that is the fact they suck at everything else, so the owners all push the one thing the cars good at


Simultaneous = win

I guess its what u define as "power". My work mate that i car pool with has a 2.5 TT manual VR4 galant, it has a nice wide power band but to me dies above 5.5k, its not standard ethier.