Cars define turbos, turbos don't define cars

[crankbender]

completely true i went on sobatical (j/k just been very busy). on the bright side the build starts somewhere around jan for the true race car. hopin to get thrown off the track for not having a full cage...

 

[Groomz]

Originally posted by 14.5 drift
Okay, am good with the flow thing. Alot of missinformed sob's tried to explain this to me, the best they could come up with was, "I dont know it just flows more air" They tried to explain to me the blowing through the straw thing but, doesn't matter if there is a ten year old or a full grown man blowing on that straw because if they are both blowing only 10 lbs of pressure then there is no air ecaping the end of the straw any faster out of the adults straw. The only actual difference could be the cooler air charge would register as more Oxygen through the maf. You guys dont know how much that has bee bugging me

I may not be correct so feel free to correct me. If you ( 14.5 ) are asking what is the difference between psi and cfm or how to understand it, I think this is how to.

PSI is a given pressure at a single moment. If you put your finger over one end of the straw, you can push out 10psi all day if you can hold your breath. Or you could blow as hard as your lungs could stand and hit 60psi for a few seconds ( just an example ).

Now you take your finger off the straw and maintaining that 10psi of pressure is more difficult. You now have to stop and take breathes to continue to flow enough for 10psi.

Now a T25 will flow 250cfm's max at 15psi. That's not alot as we all know. The 4G63 is very capable ( even 2G 7 bolts ) of flowing more air, its just the turbo is too small. Swap to a small 16G. They flow 505cfm's at 15psi. So you go out and drive the car at the same boost ( 15psi ) as the T25, but nows there's more power. CFM's right.

The cfm rating is over time, or per minute in this case. If X horsepower is achieved at 15psi @ 250cfm's ( and the engine is capable of flowing more ), then you will gain horsepower at 15psi by flowing more cfm's.

Think of it this way. Grandpa can't breath really well, so he can only get 10psi out of the straw for 2 seconds. You young guy can get 10psi for 30 seconds because your lungs have greater capacity and flow more. Kind of like a turbo which flows more cfm's at the same psi.

This may be completely wrong and I should be banned for this ( ), but this is how I understand it. Tell me if I'm right or if I'm wrong so I stop spreading heresay.

Many thanks and good boosting.

 

[crankbender]

Quite close in fact i will clarify some things you probably have right but may not have been clear.

Swap to a small 16G. They flow 505cfm's at 15psi

max. This number assumes the engine will use all those CFMs at 15 psi.

Think of it this way. Grandpa can't breath really well, so he can only get 10psi out of the straw for 2 seconds. You young guy can get 10psi for 30 seconds because your lungs have greater capacity and flow more. Kind of like a turbo which flows more cfm's at the same psi.

This could be a little confusing. Look at it this way....grandpa can try and blow as hard as you but it will only give him a coronary and he'll die.

 

[14.5 drift]

If you take a 2liter bottle and turn it upside down water will fall out of it. Think of this as a na motor. If you take a bottle turn upside down and then squeeze the bottle with 10lbs we will call this forced induction. Consider the bottle neck to be the motor. The only real way to get the water out any faster is to either .! make the hole bigger (port the motor or stroke the motor or some thing that lets more air pass through) or .2 apply more pressure to the bottle. Please try and under stand that no matter wich way you squeeze the bottle at 10 lbs the same amount of water will flow out. Meaning there will be no changes in cfm no matter how you look at it.

How ever the properties of oxygen responds to heat differently. If water is heated it will displace the same amount of space in the bottle as if it were cooled. Oxygen will not. If you were to fill a cup with oxygen and fill another with hot oxygen it will displace more than a cup full of cool oxygen, but would still have the same content of molecules. The only way a larger turbo would be able to supply more power is by providing a cooler air charge. In turn the cooler air charge will host more oxygen molecules per square inch and when the denser oxygen charge reaches the motor, it makes a bigger explosion. So as long as the smaller turbo is within it's efficiency range of providing a cool air charge then there is not going to be any benifeits to the larger turbo. So basically the t25 and t88 at 8 lbs are performing the same tasks at the same efficiency rate. No gains there.

 

[14.5 drift]

so if cfm is a measurement of oxygen density and not mass then I guess were on the same page.

 

[crankbender]

Originally posted by 14.5 drift
so if cfm is a measurement of oxygen density and not mass then I guess were on the same page.

No it isn't....we are not on the same page.

CFM....cubic feet per minute.

 

[Cesar]

pumps create flow of air or liquids (not pressure)...example:
oil pump, water pump, turbo(CFM), etc,etc...

Restrictions create pressure (PSI)...example
Main bearings, connecting rod bearings, thermostat, throttle plate, valves, etc, etc...

Turbos are advertised with flow rates not pressure readings. Turbos do not create boost, they simply keep flowing until they are no longer driven or when they reach compressor surge.

Hope that helps

 

[DCJ98GST]

Originally posted by 14.5 drift
If you take a 2liter bottle and turn it upside down water will fall out of it. Think of this as a na motor. If you take a bottle turn upside down and then squeeze the bottle with 10lbs we will call this forced induction. Consider the bottle neck to be the motor. The only real way to get the water out any faster is to either .! make the hole bigger (port the motor or stroke the motor or some thing that lets more air pass through) or .2 apply more pressure to the bottle. Please try and under stand that no matter wich way you squeeze the bottle at 10 lbs the same amount of water will flow out. Meaning there will be no changes in cfm no matter how you look at it.

Damn, your still not getting it!

To extrapolate on your example: Take your two liter bottle but this bottle is different it has 2 necks and the water travels from the bottle to the first neck (engine restriction) then to the second neck (turbo restriction) then outside. The first one has a 1" diameter opening (engine) and the second a 1/4" diameter opening (T-25 exhaust turbine housing). You will only flow as much as the second opening - or 1/4" diameter because it is more restrictive. The chamber between them is the exhaust manifold, which will have positive pressure.

Now say you move to a 3/4" diameter second opening (bigger turbine and housing) now you can flow more becase the second restriction (turbo exhaust side) is less restrictive. Same engine. GET IT!

The engine is not the only bottleneck the turbo is there too. Yea, the thing after the exhaust manifold and before the exhaust.

Now re-read my first post of this thread and maybe you will understand.

 

[14.5 drift]

Originally posted by DCJ98GST
GET IT!
B]

DONT YELL AT ME!!


Wow this is a really big equation type of shit here. So for the flow to even matter you have to first have a restriction (this just helps me visualize, so shut up). Okay now the t25 is efficient at say 8-10 psi in our cars. The reason I say 8-10 is cause my top end (after 5k) starts to get soft so i think it is running out of steam at 12. So the motor is actually just the middle part of the neck as the first would be the intake port on the turbo and then the third neck would be the exhaust side of the turbo. With the small ports that are literally on the exhaust/intake side is creating alot of build up, even before the maxing out the actual motor. So your saying that the actual resistance is not coming from the motor but the exhaust side of the turbo, correct? Hence why a larger turbo with out internal or head modifications can "flow" more air? See the hole time I was not thinking that far ahead in the chain there. I was too hung up on the motor, . Okay I am with ya now guys, carry on.



Okay this triggered a new question, how much flow can the 4g accept with out internal modifications? At what point is a bigger turbo become useless?


I hate it when you answer your own questions . Never mind. I guess at that point given no resistance from outside forces ea. turbo porting, thats why they call it forced induction cause you can just cram more air into it . Alright, I feel like I have taken a good step here so i will end my newbie rant here! thanks guys

 

[kpt4321]

14.5 Drift-

Here's how it works:

Let's not think of power in terms of CFM, lb/min, g/sec, g/rev, or anything else. Let's think of it in terms of number of molecules.

The power a motor creates is caused by the pressure created when the charge air and the fuel explodes. Thus, the "size" of the explosion determines how much power you will make. Assuming a constant A/F ratio, the amount of air molecules entering the motor is what determines how much power you are going to make.

Now, let's discuss how a turbocharger increases the number of molecules.

Are you familiar with PV=nRT? It's called the ideal gas law, and while it doesn't not work perfectly under extreme conditions, it is a good example of what is going to happen. P is pressure, V is volume, n is the number of molecules, R is a constant, and T is temperature.

If you move the terms around and just ignore the constant, we get:

n = PV/T

However, since we're talking about one motor that isn't changing in size here, V (volume, displacement in this case) is no longer changing either. Therefore, we simply get:

n = P/T

So, look at what happens. When pressure increases, n increases. When T decreases, n increases.

Real world example:

Let's say that we have a 2 liter bottle (which is fitting, as it matches the displacement of a 4G63...sorta). At the start of our experiment, it is filled with air at atmospheric pressure (14.7 psi) and room temperature (we will call it 70 degrees F).

Let's change some things and see what happens.

First, we hold the temperature constant, and increase the pressure. How do you increase the pressure, or in other words, if the pressure increases what must be happening? If the pressure increaces for a constant volume (the size of the bottle is not changing, obviously) and a constant temperature, then there MUST be more air molecules within th bottle.

Pressure is simply a measure of the force the air molecules are exerting on the bottle. When you have more air molecules, they smack into the walls more often, and you get more pressure. Pretty simple.

Now, let's hold the pressure constant, and decrease the temperature.

When you decrease the temperature, you are decreasing the average kinetic energy of the air molecules. This means that they are not moving as fast, which means that they are smacking into the sides of the container less. Thus, if the number of molecules remains the same and you decrease the temperature, then the pressure will also decrease. Sinc we are not letting the pressure decrease, what has to happen? As the temperature decreases, the number of molecules in the container must increase.

Lower temperature with more air molecules means the same amount of "wall smacking" as an end result, and therefore the same pressure. However, we now have more molecules, so the motor would make more power.

Hopefully all of this makes sense.

Increasing the pressure of something, such as the air entering a motor, increase the number of molecules which fit within a certain volume. Decreasing the temperature does the same thing.

You cannot use water in a bottle as an analogy. You see, liquids do not have the same properties as gasses, so you cannot compare them in this case. When a liquid is under pressure, the density (number of molecules for a certain volume) does not really increase.

Therefore, in your example of squeezing the bottle, the amount of water that was fitting through the hole would be the same in both cases. If there was a gas in there, when you increased the pressure the density would increase, and more air would fit through the hole.

 

[14.5 drift]

Originally posted by 14.5 drift
so if cfm is a measurement of oxygen density and not mass then I guess were on the same page.

 

[kpt4321]

It's not a measurement of density, or oxygen density.

So, we're not on the same page.

 

[leet]

CFM = Volume.

PSI = Force.

Kinda like volts and amperes.

It's been a long day so if I messed that up, PM me, smack me around, and I'll fix it.

 

[crankbender]

Originally posted by leet
CFM = Volume.

PSI = Force.

Kinda like volts and amperes.

It's been a long day so if I messed that up, PM me, smack me around, and I'll fix it.

Watch out somebody may just want to smack you around for "other" reasons.

Pressure can be looked at as a driving force like volts. However unlike electric circuits gasses can easily change energy states (pressure can turn into velocity in a nozzle etc)

I think i am just gonna ignore 14.5 untill he starts asking questions and stops making statements. No offense 14.5 but it is hard to correct a statement cause we don't know where you thinking went wrong

 

[leet]

Originally posted by crankbender
Watch out somebody may just want to smack you around for "other" reasons.

Pressure can be looked at as a driving force like volts. However unlike electric circuits gasses can easily change energy states (pressure can turn into velocity in a nozzle etc)

My bad, I forgot about that! *smacks self*

 

[14.5 drift]

Originally posted by leet
CFM = Volume.

PSI = Force.

Kinda like volts and amperes.

It's been a long day so if I messed that up, PM me, smack me around, and I'll fix it.

So under cooler conditions the volume of air molecules will be more abundant while displacing the same mass amount of air as a heated charge. correct? If this holds true then that is my reasoning behind my reference to density. But volume is still not right I dont think. It is not implyant of the character of the volume. You guys are tak=lkin to me like I am not even close. I hate this. Now i will go beat my self up.

 

[crankbender]

Originally posted by 14.5 drift
So under cooler conditions the volume of air molecules will be more abundant while displacing the same mass amount of air as a heated charge. correct? If this holds true then that is my reasoning behind my reference to density. But volume is still not right I dont think. It is not implyant of the character of the volume. You guys are tak=lkin to me like I am not even close. I hate this. Now i will go beat my self up.

Lol use a whiffle ball bat....it is easier to recover and you still get your agressions out.

The number of air molecules in a given volume will be higher. This means there will be more mass in that given volume.

There is not "mass ammount of air" when speaking of displacement.

Mass is how many molecules...displacement is how much space. The 2 quantities are coupled by temp and pressure.

 

[kpt4321]

Originally posted by 14.5 drift
So under cooler conditions the volume of air molecules will be more abundant while displacing the same mass amount of air as a heated charge. correct?

First of all, what the heck does "the volume of air molecules will be more abundant" mean?

Under cooler conditions ate the same pressure, LIKE I SAID IN MY POST, the number of molecules in the predetermined volume will be greater.

If this holds true then that is my reasoning behind my reference to density.

No.

Density is mass per volume. CFM is cubic feet per minute. Cubic feet. That is pure volume.

Density gives you no indication whatsoever of how much of something you have, not by itself.

Mass tells you exactly what you have.

But volume is still not right I dont think. It is not implyant of the character of the volume. You guys are tak=lkin to me like I am not even close. I hate this. Now i will go beat my self up.

Volume is not right for what?

CFM is volumes per time.

 

[14.5 drift]

The amount of one cooled molecule has less displacement than one that was heated, correct?

OK OK I was thinking of volume in a singular sense, I see how it would apply in this case now. So I am clear on the volume description.

cooler air provides more volume of oxygen particles?

wich means more cfm?

and more power?

less resistance?

 

[crankbender]

 

[14.5 drift]

Originally posted by crankbender

GOD DAMN IT!!!!!!! Can any body direct me to corky bell online, or some place with some descriptive literature for me. heheh maybe some pictures. This is killin me as well as you guys. Just help me find some literature I swear I will read it like 7 times.

 

[DCJ98GST]

http://www.gnttype.org/techarea/turbo/turboflow.html

http://www.gnttype.org/techarea/turbo/intercooler.html

http://www.turbocalculator.com/how-to-read.html

http://www.turbofast.com.au/tfcalc.html

http://not2fast.wryday.com/turbo/glossary/turbo_calc.shtml

http://www.stealth316.com/2-turboguide.htm

http://www.stealth316.com/2-3s-compflowmaps.htm


That should keep you busy for a while

 

[kpt4321]

Originally posted by 14.5 drift
The amount of one cooled molecule has less displacement than one that was heated, correct?

A molecule has the same displacement no matter what the temperature is. It will be moving at a higher average speed when the temp is higher.

cooler air provides more volume of oxygen particles?

NO!

The volume is always the same! When you cool the air, the size of the motor isn't changing!

Cooler air lets you fit more molecules into the same space. Higher density, higher mass, more molecules, same volume.

My big post did cover all this.

less resistance?

I'm not even sure what this means.

 

[kpt4321]

Originally posted by 14.5 drift
Can any body direct me to corky bell online, or some place with some descriptive literature for me...Just help me find some literature I swear I will read it like 7 times.

This thread would be a good start.

 

[Eagle 5]

here's a little something to consider. I work at GE Aircraft engines in the marine and industrial dept. (as a co-op right now) WE have anew gas turbine coming out. currently the most power we make is around 45 MW (mega watts) which is around 60,000 shaft horsepower. The new one coming out will make around 104 MW which is around 105,000 shaft horespower. Heres the main differences.

The new one has an Intercooler (Air or water cooled), this sits between the "booster" or low pressure compressor (LPC) and the high pressure compressor (HPC). it cools the air after the LPC before it goes into the HPC. This new engine runs temps right before the HPC of about 200-300+ or more degrees cooler than the current one. Also it creates higher pressure , about 100+psi more. Running the coole air before the HPC and making more pressure, the gas turbine can burn more fuel and run to higher temps after the combustor. because the intake air is colder now, by a significant amount and at high pressure. colder air and more fuel gives more power, it also flows more air too.

now, in order for teh combustor to work properly there has to be a pressure drop, without the pressure drop the air wont flow correctly and the flame would go out. in an engine, there is a pressure drop between the air before and after burning, otherwise it would not work. so by flowing more, colder air at higher pressures, you make more power. or even at the same pressures but much colder, more power is made. not sure if that helps any but at least gives an idea of how air at same pressure but mcuh colder will make mroe power, also it will be mroe efficient