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).

 

[killakev805]

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).

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.

 

[turboinside]

There is alot at stake here. One turbo can flow more CFM's at a lower p.s.i. than another. Then you also have HEAT! Our stock turbo's on our belved DSM's are pretty weak for performance. Once you boost to 15p.s.i. or better, then it starts to puke out alot of heat. It is just being pushed to its limits. The stock turbo is only inteded for ~10 p.s.i. To get the most out of a turbo isn't always about preasure (although that helps alot) But about eficiantcy. That is why you need to figure out what your particular needs/wants are, then cunsult the turbo maps for the blowers you want!

 

[gsxeclipse97]

yes a bigger turbo will flow more air because it doesn't heat up has much. The intake manifold only reads psi it doesn't see the cfm.. Thats why you can turn up the boost on a t25 and not kill your motor but if you were to do that on a 16g or a 14b you could start breaking things..

 

[tstkl]

what happens when you get a bigger exaust,.... you get more power, right? and why is that? because even though the pressure behind the exaust (the engines CR) is the same, the new exaust can FLOW more.... same thing with a bigger turbo, a bigger turbo applying the same FORCE on the intake charge can still give you more power if it FLOWS more with that same force.... remember the main idea behind turbochargers is more air=power, and while a higher psi on the same turbo means more air, a 50 trim at 10 psi can flow more air than a 14b at 15 psi, so the 50 trim will "FEEL" faster,


but only because it is...

 

[2gPressure]

I think what I'm saying is being misunderstood.
But as long as you have enough airflow (CFM) to keep 15 psi at the intake manifold the same amount of air is going to flow into the cylinders because it is the pressure that is pushing it in. And that airflow(CFM) of the turbo is used to keep a maintained pressure in the intake manifold.

The pressure is what determines the amount of air that enters the cylinders and the CFM of the turbo is what determines how much pressure you are able to maintain in the intake manifold.

Which is why it appears to me that bigger turbo=PSI=Power. The only difference I see is heat from inefficiency and no mysterious airflow difference that no one can explain.

 

[CyberEye]

a bigger turbo will flow more cfm's at Xpsi, then a smaller turbo will at the same psi

 

[drivemusicnow]

I think what I'm saying is being misunderstood.
But as long as you have enough airflow (CFM) to keep 15 psi at the intake manifold the same amount of air is going to flow into the cylinders because it is the pressure that is pushing it in. And that airflow(CFM) of the turbo is used to keep a maintained pressure in the intake manifold.

The pressure is what determines the amount of air that enters the cylinders and the CFM of the turbo is what determines how much pressure you are able to maintain in the intake manifold.

Which is why it appears to me that bigger turbo=PSI=Power. The only difference I see is heat from inefficiency and no mysterious airflow difference that no one can explain.

... you're thinking about this all wrong. First of all, think of the "gas" pedal as actually an AIR pedal. because all you do when you open the throttle body is allow more air in. Now, if a 14b flows X amount of air into the cylinders, the ECU adds the "correct" amount of fuel, and combustion happens.

now, when thinking about boost pressures, you must realize that pressure is the resistance of flow. think about a water pipe. you keep forcing water into a very restrictive pipe, you get a lot of pressure, but not much flow... you open that pipe up, you get much more flow, much less pressure.

What a larger turbo actually does, is puts a larger VOLUME of air into the cylinder. soo that 14b is flowing x amount of air, while my 60-1 is flowing 3X amount of air, and the same pressure.
because we control boost by pressure, a lot of people think that the pressure is what actually "makes power" and thats just not the case.

(just realized how hard this is to explain... hope that helped)

 

[2gPressure]

more cfm at same psi?

that was very simple and confusing.

it sounds like you could reword that as it has the potential to increase the PSI to past what the smaller turbo can create.

Where are all those CFM's going that the bigger turbo is pushing compared to the smaller turbo? You say into the cylinders the extra CFM's go? it is not into the cylinders because the amount of air entering the cylinders is determined by the pressure in the intake manifold and the resistance going into the cylinders which is the valve openings.

I say it is not pushing them because the wastegate is slowing the turbo down. Though if you turned the PSI up it would be using the extra CFM

 

[2gPressure]

now, when thinking about boost pressures, you must realize that pressure is the resistance of flow. think about a water pipe. you keep forcing water into a very restrictive pipe, you get a lot of pressure, but not much flow... you open that pipe up, you get much more flow, much less pressure.

That explanation doesn't work because you are creating a bigger pipe that has larger ends on both sides. One "end of the pipe" is the valve inlet to the cylinders which doesn't get bigger(same resistance no matter what turbo) so you would have to use the example if you open the pipe up all except the end of it, which would flow the same as it wasn't opened up


someone has to start understanding what i'm saying then you would start agreeing and wondering just like I am!

 

[CanadianTSi]

2gpressure, if what you think is true, then why does it require a big turbo to run fast times(i'm talking like 10's and faster...)???

All the big dogs would run little turbo's since xpsi is xpsi regardless, this isn't the case...

 

[98eclipseRS]

That explanation doesn't work because you are creating a bigger pipe that has larger ends on both sides. One "end of the pipe" is the valve inlet to the cylinders which doesn't get bigger(same resistance no matter what turbo) so you would have to use the example if you open the pipe up all except the end of it, which would flow the same as it wasn't opened up

I'm thinking everyone is thinking of it wrong, no offense to anyone

no you are thinking of it wrong sorry, no offense. I posted a reply in the other thread but unfortunately I don't think you will understand it. I am going to try and explain in very simple terms the best I can.

It doesn't matter how how small or large the intake valves are you can flow more air past them than they can flow by themselves. That in theory is what a turbo is for. To stuff more air into the the engine than it would have at the beggining.

Imagine the pipe example this way. The ends of the pipe are not the engine and the turbo. The ends of the pipe are the opening to the turbo and the outlet pipe on the comp housing. The engine is a big tank on the end of the pipe. Regardless of the flow of the pipe the engine(tank) can recieve as much air as you can shove at it. Now which pipe is going to flow more volume a 3" pipe or a .5" pipe? The three inch pipe will flow more volume. That is the larger pipe can move more water through it.

Just like drive music said pressure is a measurment of resistance of flow. Say you have 15 gallons of water to move through a pipe to the other side. both sides of the pipe open into the open air. You have to move the 15 gallons as quickly an efficiently as possible.
Now you have a pump that will only flow 15 psi of water pressure. If your pipe is .5" in diameter and you are trying to move 15 gallons of water as fast as you can its going to take a while. Your .5" pipe will hit 15 psi of flow(the resistance of the water moving through the pipe) at say 10lph(liters per hour). However your 3" pipe will move 40lph at 15 psi. Why is this. Because there is more room to flow water through, becuase there is more room there is less resistance made by the pipe, ou could consider this psi. So at the same psi you are flowing 4x as much volume of water.

Since you are trying to move as much water as fast as possible the larger the pipe(turbo) the better off you are.

 

[2gPressure]

Here is exactly what I'm talking about:

If you have a large ball and you have two holes in it and one of them is a tiny hole letting air escape and the other is a hole forcing air in. If you maintain 15 psi in that ball no matter what the same air is going to flow out of the tiny hole. If you increase the size of the hole pushing air in and you are still maintaining 15 psi the air out the tiny hole will be the same. If you increase the CFM's into the ball through the inlet hole you will increase the pressure in the ball because you pushing too much air in for what is leaking out and you will no longer be at 15psi. The only way to increase the amount of air out the hole (into the engine) is to increase the pressure or create a larger outlet hole (port the head).

my point still stands larger turbo=psi=power!
except for some heat innefficiency

 

[98eclipseRS]

go to the other post I made please I exlained why that doesn't make sense either. the airflow into the cylinders is determined by the pressure at the intake manifold and the resistance going into the cylinders

^^from the other thread. So are you seriously trying to tell me(an hvac mechanic) that I don't know about flow/psi/and pressure drop? or that everyone else that is trying to explain this to you is wrong? Did you pay attention in highshool chem class as to why denser air has more volume to it than less dense air? Airflow to the cylinders is determined by CFM nothing else. PSI is ONLY used to messure how hard the turbo is working nothing more. AirFLOW is determined by volume which is determined by the amount of molucules of a particular gas you can fit into a given area in a certian time, If you don't understand that I don't know what else to tell you.

 

[98eclipseRS]

Here is exactly what I'm talking about:


my point still stands larger turbo=psi=power!
except for some heat innefficiency

You do realize it not for SOME heat innefficiency its all about heat transfer.

Also larger turbo=psi=power what?? PSI what?? that doens;t make sense. Here for the simplest terms in the damn world. Strap a car with a t25 to a dyno at 15 psi see how much power it makes. Next strap the same car with the same mods ot a dyno with a 50trim at 15psi and see which one makes more power.

 

[drivemusicnow]

haha i think i've figured out his logic mistake...

2gpressure. are you assuming that 15psi pressure equals 15 psi in the cylinder? pressure is just a force. higher pressure outside the cylinder just makes the force of air rushing in higher, it doesn't not change the amount of air.

the actual VOLUME/AMOUNT of air, is determined by flow.

 

[gsxeclipse97]

This is how someone explained this in another thread i read
think of a t25 as a straw from mc donald's. Now think of a 50 trim as a tolet paper roll.
Now you are going to blow 15 psi through the straw and 15 through. The roll is going to flow much more air at the same psi than the straw. Same goes with turbos. Heat is also a factor but thats the idea

 

[98eclipseRS]

This is how someone explained this in another thread i read
think of a t25 as a straw from mc donald's. Now think of a 50 trim as a tolet paper roll.
Now you are going to blow 15 psi through the straw and 15 through. The roll is going to flow much more air at the same psi than the straw. Same goes with turbos. Heat is also a factor but thats the idea

he doens't get that example it was already explained to him that way, the problem is he keeps thinking of one end of the straw as the turbo and the other end as the engine. Where as to understand this correctly you have to think of the straw as the turbo and the open atmosphere as the engine.

 

[2gPressure]

The straw and paper towel roll explanation is not how it works because the resistance of the tube is the same as the resistance to the air going into the cylinders and if you increase that you are increasing the size of the valve ports.

bigger turbo=psi=power

 

[huafist]

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.

 

[2gPressure]

^^from the other thread. So are you seriously trying to tell me(an hvac mechanic) that I don't know about flow/psi/and pressure drop? or that everyone else that is trying to explain this to you is wrong? Did you pay attention in highshool chem class as to why denser air has more volume to it than less dense air? Airflow to the cylinders is determined by CFM nothing else. PSI is ONLY used to messure how hard the turbo is working nothing more. AirFLOW is determined by volume which is determined by the amount of molucules of a particular gas you can fit into a given area in a certian time, If you don't understand that I don't know what else to tell you.

Airflow to the cylinders is determined by CFM and nothing else is exactly right but what determines the CFM flowing into the cylinders is the pressure in the intake manifold and the valve openings.
Since the valve opening in a constant resistance how can you have more flow(CFM) with the same pressure.
Not including the efficiency heat

 

[Littlebeeper]

Man i just waisted 15 minutes of my life typing a big explination for this crap of Turbo=PSI=Power. what you need to do is stop thinking as a turbo blowing "air" and there being more "air" flowing into the engine at a higher PSI. If it were that easy then why the hell do Intercooler exist. You say forget about the "heat ineffeciency" but thats one of the main points governs how much power we can make at a certain PSI. think of this and forget about AIR. Take any car, Turbo or not. I bet you anything you want that if you ran the quarter mile in Arizona in the middle of the day and in the middle of summer, then try running that same car at the same track in the middle of the night you will get better E.T.'s at night. Now let be change this around and ask you a question. the cars valves are exactly the same. its getting the same "AIR" past them at night and in the heat of the day. So, my friend, why did the car go faster at night?

 

[huafist]

Airflow to the cylinders is determined by CFM and nothing else is exactly right but what determines the CFM flowing into the cylinders is the pressure in the intake manifold and the valve openings.
Since the valve opening in a constant resistance how can you have more flow(CFM) with the same pressure.
Not including the efficiency heat

Not 100% correct. For one, pressure != CFM. Think of pressure as speed. The pressure difference between two bodies is what determines how "fast" a fluid (in this case, air) moves. The volume is irrelevant, it doesn't care. A bigger turbo makes more power because the volume is larger, yet the speed is the same. (Back to the Boyle's Law explanation). The reason you make more power at a higher psi on a big turbo is because the air isn't heated as much, so you can push more into the combustion chamber.

 

[drivemusicnow]

Okay, we're going to start this ONE more time...

First of all, saying bigger turbo = more psi = more power is OBVIOUSLY flawed. realize this.

as people ahve stated when you put a larger turbo on a car, it makes more power at the same pressure.

Second... a turbo is a compressor. which means that it physically compresses air before it lets it go. it creates a "charge" of compressed air. its not the flow of the turbo that creates the compression, it is teh physical act of the compressor wheel hurling air into a smaller cavity that creates pressure.

Third, power is made of flow of air through the engine. The more air in the cylinder, the more fuel, the more power. Now, if 15 psi of manifold pressure yielded a perfect 15 psi of pressure inside the cylinder, then your example may be correct. HOWEVER valves open and close very quickly. Quick math yeilds that valves open and close 350 times per minute at idle, equates to in one minute, which means that they are open for about .07 seconds each rotation of the engine. Now heres the kicker.. how much air can flow into the cylinder in that time. now FLOW!!!!!!! of air is what your'e looking for... not pressure.


and its late, so excuse any stupid mistakes

 

[98eclipseRS]

The straw and paper towel roll explanation is not how it works because the resistance of the tube is the same as the resistance to the air going into the cylinders and if you increase that you are increasing the size of the valve ports.

bigger turbo=psi=power

alright well since you are so stuck on the same size opening regardless of pipe size let's look at just flow, just flow.

Air+fuel+spark=power.

PSI is a measurment of the resistance of flow of a volume of through a certain area.

The more molecules of oxygen(air) per given space the denser the aircharge

The denser the aircharge themore power you are going to make.

If I have lost you so far go back over it untill you get it. Now since the goal of a turbocharger is to cram as much air into the cylinder as you can. You want the most dense aircharge possible. Why? well the denser the aircharge the more molecules of oxygen per area and we learned earlier that air(oxygen) is a key ingrediant in our quest for power.

So there are several ways of getting more air into the engine. You can up the amount of air going into the engine by upping the boost. Now upping the boost does not neccasarily mean more air molecules it just means more friction between the air and the intercooler pipes.

The other way off getting more air into the engine is through a much more dense aircharge. Meaning more molecules of oxygen per given area.

Now the more you have to compress the air to get into your engine the more it heats up and therefor the less molecules of air being put into the engine.

So:

as temp rises molecules decrease

compressing air creates friction=heat

heat is bad


Now on a small turbo such as the t25 the area that the air must be compressed in(comp housing) is very small. This means the turbo has to work very hard to move the same amount of air(cfm) at a given psi. Because the comp housing is so small only a small amount of air can occuypy the space efficiently, So when you are trying to cram more air than the turbo can effectively handle it heats up to extreme temperatures because you have to compress it so much. And has we know the more you have to compress the more heat is created through friction. The more heat created through friction the more heat is transfered to the air charge. And the more heat in the aircharge the less molecules of air that can ocupy a certain area.

Now when you have a larger turbo you effectively have more room to compress the air correct?(compressor housing is larger) Having a larger space to compress air means less friction and a more dense air charge. Since Psi is the measurment of the friction of air through a given area. 15 psi is 15 psi correct? However here is where ALL the diffreance is, with the larger turbo the aircharge is denser. YOu still have the same amount of friction throug the pipes yet you have MORE MOLECULES OF OXYGEN in the air that is being forced through the pipes.

remember:

air+fuel+spark= power

so if we had more air molecules then we will make more power.


Your mistake is dismissing the heat transfer of the compression process as insignificant. If it played such a small role in the power equation no one would run fmic or air to water intercoolers. Here is another example that proves your theory wrong and hopefully explains this better.


take your car on the t25 at 15psi and dyno it on a day that is 40* outside. Now dyno it with the exact same setting on a day when it is 80* outside. If you don't make more power on the day with it being 40* outside I will eat my shit and videotape it for you, but why do you make more power?

On the day when it is warmer outside the aircharge you are stating with is much less dense, add this to the fact that the small comp cover is raising temp levels to extreme temps means that you have alot less air molecules in the air charge than on the day when it is 40* outside. With this example you can see why psi is not important but the amount of air molecules you can get into the engine is what is important. So its volume of molecules not the resistance that the charge creates that is important.