bigger turbo = psi = power?

[2gPressure]

Is that right? no matter what turbo you are running if you can hold the same PSI you will get the same power, except for the small difference of inefficient turbos disappating more heat into the intake air.

Most people say a bigger turbo has more airflow so you get more power at the same PSI which doesn't seem right.

I'm thinking with a free standing turbo blowing into the air it doesn't create any pressure right? So you could say the airflow of the turbo is creating the pressure in the intake manifold and then that pressure in the intake manifold is creating the airflow into the cylinders. The airflow of the turbo shouldn't matter so long as there is enough airflow to hold the pressure at the intake manifold, which that pressure is determining the airflow into the engine not the airflow that is used to maintain that pressure(turbo).

 

[2gPressure]

For the love of God.
THE AIR IS COOLER WITH A BIGGER TURBO THUS DENSER! THE PHSYCIAL SIZE OF THE CONTAINER ISN'T CHANGED! YOU CAN PUT MORE AIR INTO A GIVEN SPACE AT A LOWER TEMPERATURE!
Take a look at Boyle's Law. If you take a container with air in it, say, 15 psi. If you cool that container, the pressure goes down. Why? Because the air is cooler, denser, and not exerting as much force. Inversely, if you heat it, pressure rises because the air becomes hotter and the space between the molecules increases as they take on more energy.

If you don't understand that, then you need to just give up now.

There you go! Everyone else was saying that you are increasing the airflow but all that you are really doing is lowering the air temperature, by upgrading the turbo. is that right? so you would achive more hp gain with a FMIC on a T25 than you would with a 14b at around 12 psi?

 

[huafist]

There you go! Everyone else was saying that you are increasing the airflow but all that you are really doing is lowering the air temperature, by upgrading the turbo. is that right? so you would achive more hp gain with a FMIC on a T25 than you would with a 14b at around 12 psi?

It does result in more airflow. The volume of air being moved is larger. I don't have the numbers in front of me to answer the question about the FMIC, but it would stand to reason it wouldn't make a large difference because the charge of air coming out of the T25 will still be hotter than the charge coming out of the 14b, thus making the intercooler work harder to cool it down.

 

[2gPressure]

okay you are not increasing the CFM because the CFM doesn't include temperature,

whether it is hot or cold air flowing CFM is the same for the amount going through a point.

Cubic Feet Per Minute (CFM): A unit of measurement for airflow. For example, 100 CFM is moving 100 cubic feet (about the amount of air in a VW Beetle) of air in one minute. CFM is typically measured at the point of introduction into the space

People were confusing with their posts.

Put simply: With a smaller turbo you are decreasing the volume of air because the turbo is heating the air up so much that it is losing density. You have 15 psi of air at the intake manifold but it is extremely hot air. It is a little scetchy saying that you are increasing airflow or CFM because what you are really doing is pushing cooler air which means more oxygen molecules.

Thanks for the long explanation zach, it was interesting to know exactly how and why there is the difference. I'm sure half the people that posted didn't know this either.

I was thinking that the power to be gained was from a decrease in pressure required in the exhaust manifold to spin the turbo, so it would reduce the backpressure and the exhaust would flow out easier. Is that right too?

 

[dirk3]

Let me try...

Lets say you have two household fans. One is 12" in diameter and the other is 16" in diameter. You have it rigged so they both spin at the exact rpm. The larger fan will push more air at the same rpm. The psi doesn't change, just the amount of air being pushed. More psi means more cfm. But a larger blade also means more cfm, at the same psi..

 

[98eclipseRS]

okay you are not increasing the CFM because the CFM doesn't include temperature,

whether it is hot or cold air flowing CFM is the same for the amount going through a point.

People were confusing with their posts.

Put simply: With a smaller turbo you are decreasing the volume of air because the turbo is heating the air up so much that it is losing density. You have 15 psi of air at the intake manifold but it is extremely hot air. It is a little scetchy saying that you are increasing airflow or CFM because what you are really doing is pushing cooler air which means more oxygen molecules.

Thanks for the long explanation zach, it was interesting to know exactly how and why there is the difference. I'm sure half the people that posted didn't know this either.

I was thinking that the power to be gained was from a decrease in pressure required in the exhaust manifold to spin the turbo, so it would reduce the backpressure and the exhaust would flow out easier. Is that right too?

your getting closer in your understanding but not quite there yet, almot though its not the easiest concept to grasp or explain so learning this in a short period of time is rather hard. Your first statement is true you are decreasing the volume of with a smaller turbo because of the less dense aircharge. CFM is used to measure the amount of molecules going through a certain area. Where as PSI is used to measure I gues you could call it speed maybe that the air is moving at through the same area.

Here is an example that might help you with this. Say you are moving 10 air molecules through a given area(CFM) at 10 mph your pressure rating for this equation is say 12psi. Now you are moving the same 10 molecules of air through the same area at say 15 mph, now the pressure rating for the same amount of air flow is 18psi. (these numbers were completely made up just examples) Hope this helps.

As for your second question yes and no. Yes, less pressure is created in the manifold and exhaust does flow easier thanks to the larger turbine housing. However just reducing manifold pressure doesnot give you direct hp gains but it does help you be able to run more manifold pressure(psi, or just more air molecules entering the engine.) It has alot to do with VE, just as with a turbo an engines goal is to get as much air in and out as quickly as possible. By making the intake and exhaust track more efficient you are allowing the engine to breath more freely and as in my last example..

more air+more fule=more power.

 

[BulliT]

I am not sure how to explain it to you, but your statement is incorrect. The only proof I can offer is that when I had my t25 at 15 psi on my car, it was slow, but after I put my 14b on, my car is faster at 14 psi. I didn't change anything else, I just put a bigger turbo on and now it is faster. So that is my proof.

Really ? there was a video in the lounge a while ago of a 14B(15psi) AWD vs a FWD T25 GST(only modifications were a BOV), the GST won by a nose.

 

[drivemusicnow]

Really ? there was a video in the lounge a while ago of a 14B(15psi) AWD vs a FWD T25 GST(only modifications were a BOV), the GST won by a nose.

I don't know if you're trying to be a smartass... or if you're just stu... not smart, however comparing different cars, with different amounts of powerloss, with different modifications, with different drivers, and different turbos does not seem to be a very scientific test... lets try for under 4 variables next time. preferably the typical 1 variable used in any REAL test.

Its a common known fact that the 14b is larger and therefor has the capability to create more power.

 

[2gPressure]

your getting closer in your understanding but not quite there yet, almot though its not the easiest concept to grasp or explain so learning this in a short period of time is rather hard. Your first statement is true you are decreasing the volume of with a smaller turbo because of the less dense aircharge. CFM is used to measure the amount of molecules going through a certain area. Where as PSI is used to measure I gues you could call it speed maybe that the air is moving at through the same area.

Here is an example that might help you with this. Say you are moving 10 air molecules through a given area(CFM) at 10 mph your pressure rating for this equation is say 12psi. Now you are moving the same 10 molecules of air through the same area at say 15 mph, now the pressure rating for the same amount of air flow is 18psi. (these numbers were completely made up just examples) Hope this helps.

As for your second question yes and no. Yes, less pressure is created in the manifold and exhaust does flow easier thanks to the larger turbine housing. However just reducing manifold pressure doesnot give you direct hp gains but it does help you be able to run more manifold pressure(psi, or just more air molecules entering the engine.) It has alot to do with VE, just as with a turbo an engines goal is to get as much air in and out as quickly as possible. By making the intake and exhaust track more efficient you are allowing the engine to breath more freely and as in my last example..

more air+more fule=more power.

I don't care for reading books but I would probably be better off with finding a text book. There is far too much theory to put in a forum and it is much easier to show points with set in stone equations and formulas rather than examples.
CFM should be the velocity of the air and time because it is measured in time and you could fill up more or less area if velocity were increased or decreased. And PSI would be the amount of molecules because the more molecules in an area the more force there is on the surrounding objects which that force is the pressure in psi. The only leak to PSI being considered the amount of molecules is that temperature can change the amount of molecules in an area also.

Why does increasing the velocity to those 10 molecules you were talking about increase the pressure? is that because it is causing more heat? which raises the pressure? It looks to me like your missing resistance. I can understand that pushing 10 molecules towards a small hole at 10mph vs 15mph would increase the pressure before the hole.

Lowering the exhaust manifold pressure should create more power in itself because the pressure in the cylinders and the pressure in the exhaust manifold are battling each other as to which way the air is going to flow, though the cylinders win it would be much easier for them to push into a lower pressure area. And a larger turbo should creates a lower pressure. though it is kind of what you already said because it is a sequence of cause and effect.

One more thing that would be good to know is when you have cooler air does that require more fuel because there is more oxygen though it is in the same amount of space? or is decreasing the intake temps a winning situation? if so those water injection kits would be well worth the cost per HP.

 

[cdct99]

First off, there is a whole lot of misinformation going on in this thread, with a lot of people claiming that 2gpressure is not understanding the theory, when in fact it appears he pretty much has it. Also, I think that both sides are actually saying close to the same thing, with some blatantly incorrect posts.
That said, the turbo is simply creating pressure on the intake manifold at x psi pressure and y degrees temperature. Given these variables, one could compute the quantity of air molecules which will flow into the engine via the intake valves. Period. The straw analogy, hose analogy, etc are all incorrect except that they explain the change in temperature, which will result in a marked difference in the density of the intake charge. This therefore affects the number of air molecules entering the engine. There is a finite area for the air to flow into the engine through the valvetrain, and a set pressure will flow a set volume into the engine. 2gpressure, I think you are writing off the temperature difference as a minor change, when in fact it is a substantial difference, and entirely where the additional power comes from. Let me know if any of this needs clarification.

Hope this helps,
Steve Parry