Does x psi = x psi regardless?

[Goblin]

word

 

[danthman3]

I temporarily sed to neglect the temp diff to show that everything except that were the same leaving only one variable when looking at a turbo
on this issue i was not disageeing with you i was simply showing that what i said was another way of illustrating the same point
i may have underestimated the temp diff of two different turbos (i figured the temp diff @15psi on for example a 16g compared to a t4 would be a few degrees celcius translating to a minimal difference when converted to kelvin)

the previous statement i made about turbos flowing the same amount of air i should've written volume not amount

if PV=nRT
PV/nRT=1
1=1
PV/nRT from one turbo will equal PV/nRT from another
so if the P is constant you can cancel it (approx 15psi depending on volumetric efficiency of the motor)
and if the V is constant you can cancel it (aprox 1 liter percycle or 2 cylinders worth)
R is a constant

thanks for the smart-ass coment i'll relay it
this wasn't about who's smarter its about who replies to "correct me if i am wrong" with "Why in the hell do we use an intercooler then? For looks?"

 

[Tevenor]

 

[DCJ98GST]

Originally posted by Enigma_Man

A bigger turbo cannot just *make* more flow through the engine.

THIS IS WRONG!!

A bigger turbo with bigger turbine housing and turbine creates more efficient use of the exhaust energy and increases exhaust/engine flow (VE-Volumetric Efficiency) through the engine.

Therefore bolting on a bigger more efficient turbo will create more power by increasing the flow of the engine even if you are boosting the same psi at the same temperature!

Most of the gains of a bigger turbo at the same psi are gained by increasing the engine's VE, not cooler air as long as you are not too far out of the compressor wheel's efficiency range.

So does x-psi = x-psi at the same temperature?

No, if the engine's VE goes up.

 

[danthman3]

thats is true
i think alot of us neglected the turbine housing and looked solely at compressors
good catch

 

[GVR4#1353]

Originally posted by Enigma_Man

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at 15psi of boost the pressure of the air going inside the cylinder would be 29.7psi....just thought I'd clear that up a lil since you put 15psi for the pressure in the cylinder

 

[Enigma_Man]

I mean above and beyond VE. I know a bigger turbo gives the total system a slightly better VE. But, I just want to make it clear that just because a large turbo can, for example, flow 600 CFM @ 15 psi, doesn't mean it is GOING TO.

I'm trying to illustrate that an engine is like a pump in this sense, it will only take in so much volume of air per revolution at a certain PSI, and a bigger turbo does not make the engine take in more air, because the PSI is the same, and the RPMs are the same. Bigger turbos _do_ make more power because of efficiency increase, and temperature decrease, but not because they are somehow forcing more air through the engine.

I'm not saying that there aren't gains to a larger turbo. I'm saying that at stockish PSI, the gains _aren't_ from the turbo flowing more air through the engine. The engine will take all that it can take, reguardless of which turbo is feeding it, as long as the turbo can keep up.

-Jesse

Originally posted by DCJ98GST


THIS IS WRONG!!

A bigger turbo with bigger turbine housing and turbine creates more efficient use of the exhaust energy and increases exhaust/engine flow (VE-Volumetric Efficiency) through the engine.

Therefore bolting on a bigger more efficient turbo will create more power by increasing the flow of the engine even if you are boosting the same psi at the same temperature!

Most of the gains of a bigger turbo at the same psi are gained by increasing the engine's VE, not cooler air as long as you are not too far out of the compressor wheel's efficiency range.

So does x-psi = x-psi at the same temperature?

No, if the engine's VE goes up.

 

[LaserRST]

This is a good topic!! Well as most said in a static system 15 psi will equal 15psi as long as we are talking about an ideal gas. Other wise we will need to look at the Z factor. In our topic of turbo, and I will call it turbo efficiency, in my opinion I think by stating as such will narrow this discussion more toward our interest. We are really talking about turbo efficiency and since the turbo is the compressor source and the pressure regulator source there is much more to be said and the turbo is the focal point. Its kinda late for me and I would love to hear the opinions of both the meteorologist major and the aerodynamics major. Factors such as ambient temp, pressure on the inducer side, pressure on the exducer side, barometric pressure, intake temp, and CFM or LBSp/m has a big factor of how the psi in a large turbo and the psi in a smaller turbo are stable. First we need to look at the turbine since that is what causes the turbine to spin. This will determine how quickly the impeller will spin, setting aside things like bearing type wheel weights etc. To make things easy for us we will have two imaginary wheels, both will be tuned to their impellers to produce 15psi at the same engine speed of say 3000rpm. This will give both turbos the same escape rate at the engine. This will be at sea level with an ambient temp of 75 deg F. The first difference will be at the inducer side. A smaller inducer will produce more vacuum at the intake depending on runner size to the air filter, this is where the collegiates can help me with the numbers, but this will make a difference on the compressor maps left side. A larger impeller will have less of a draw by just plain volume. This will keep the CR lower than the smaller turbo and closer to its peak efficiency. The smaller turbo will have to spin faster to maintain the same pressure. The bottom portion of the compressor map will have to do with flow. The larger turbo will have a broader angle to produce more flow within its peak efficiency. What does all of this have to do with how their pressures differ? Well how well does that turbo replace the air escaping into the engine? A better flowing turbo and a slower spinning turbo will replace the air more rapidly as well as put more air into the engine. Pressure stability. The smaller turbo will have to spin much faster and the rate of its delivery will be unstable, fluctuate more with the engine. Its late so I will need to finish this later pbbly tomorrow. I would love to hear more formulas to bring more numbers into this. Thoug I feel I may have brought some light into the subject, there is much more going on @ 15psi that needs to be included than just air pressue at the intake plenumn. See ya tomorrow

 

[LaserRST]

K back. I didnt read all three pages when I first replied to the thread, it was late silly me. There are alot of good points. Temperature is what is next. The smaller turbo will, in result of the need of spinning much faster, excite the air molecules more causing more heat resulting in a less efficient burn in the cylinder. So far with a smaller impeller wheel we have less air entering the cylinders at a higer temp meaning less O2 when the spark plugs go off. With the larger turbo we have more air (stable) and lower temps with a more efficient burn. Now there is one more point and thats back at the turbine. We now have a turbine wheel, one on the smaller turbo is smaller to use the spent gasses to spin the impeller at a much faster rate, there is another set back and here is where the real kicker sets in. You are creating pressure here!! In order to spin the smaller wheel faster more pressure is required, fillin up the exhaust manifold and, yes, creating back pressure into the cylinders and less efficient burn. This seriously affects VE, and turbo efficiency. Some may say that if you close your exhaust valves sooner you will eliminate this, true, but you leave gasses behind still not helping. On the larger turbo there is less pressure there because more flow is passing through the turbine, hence less pressure building in the exhaust and less spent exhaust in the cylinders. This is one major factor in why turbo cars will never see VE over 95%. It is just impossible. Na vehicles will reach VE number exceeding 100% up to 110% because of valve overlap, port velocity, and swirl tactics at the piston, head, and valve. This is why BB owners say all the HP is in the head of the vehicle, this is not true on turbo cars. Yes the head is a major contender but alot of it is really at turbo selection, feul tuning and ignition timing (another reason why VE on a turbo will never reach 95%). This is why 15psi on a small turbo wont put out the same as 15psi in larger turbos. I would love it if any one could add to this or include any details in numbers, I love seeing this on paper. My .02 cents.

 

[pneumo]

OK here ya go. First, if anyone doesn't get what's been written at this point, go back and re-read. It's all there. I plan on adding another variable into this topic, and I will be making some assumptions.
As Laser RST and others have stated, there is something going on in the exhaust section that helps make power, too. A turbo's speed has something to do with it. A prime example are the compressor maps for the small 16g and the big 16G. go to www.stealth316.com/images/td05h-16gsmall-cfm.gif
and www.stealth316.com/images/td05h-16glarge-cfm.gif and print them out so you can compare side by side. I'm using these two as an example because they both use the same 7cm turbine housing and wheel. Put a dot where the 2.0 presure ratio line meets the 300cfm line. Both turbos are at their peak efficiency,the small 16g is at 77%, while the big 16g is at 71%. By the way, that's about how much air is going in the engine at 5,000 rpm and 14 psi of boost. Looks bad for the big 16 right? It doesn't get anymore efficient, why would the big 16 work better than the small 16? here's why. The numbers on the right are the rpm of the turbo. Notice that the small 16 is turning over 110,935 rpm while the big 16 is going under 105,000 rpm. The big 16 turns slower for the same boost. The advantage of the big 16 is entirely in the exhaust side, even at the expense of compressor effiiency it makes more power.
Plot another point where the 2.6 pressure ratio line meets 500 cfm line. That's about 24 psi of boost and 6,500 rpm. I know we're trying to limit the scope of this thread to 15 psi, but it's just easier to see what's happening up there. Notice the turbo rpm line again. On the small 16 that line goes nearly vertical, while on the big 16 the turbo rpm still goes across more horizontally. That means the turbo has to accellerate to maintain boost. The small 16 has to speed up much faster than the big 16. The energy to speed up the turbo comes from the exhaust of course, and to get it the wastegate opening will narrow and/ or close. All the exhaust trying to go through the restrictive turbine instead of the less restrictive wastegate will increase backpressure and limit power. The same thing is happening at 15 psi, but it's a smaller difference. After all, these two turbos are only one size apart. To see a real difference check out www.stealth316.com/images/td06h-20g-cfm.gif Notice that the 105,00 rpm line actually curves up at 300 to 400cfm area? The turbo is actually slowing down and maintaining boost! The 2.6 PR line @ 500 cfm is nicely horizontal with just a slight downcurve. Mmmm...power, (drool)
for more compressor maps check out www.turbonetics.com and www.stealth316.com which also has more juicy tech talk on turbos.

 

[DCJ98GST]

Good post!

Hopefully people will start to learn that a more efficient turbo has a lot more involved to help horsepower than just heat of the charged air. I think this is one of the big misconceptions people have of understanding how a turbo works with our engines.

 

[danthman3]

yea this really is an informative thread
and the compressor maps really illustrate pneumo's point
to go a little off topic i just got a 3kgt vr4 and i found out that 14b's are their big turbo's (cuz they use two) up to 550hp worth
i thot it was interesting

 

[LaserRST]

I wonder how to imput the math if we were to go twin turbo? Parrallel or serial... I saw one on ebay and the seller claimed it to be able to push 500+ HP for our 4G63s. I think if we can put that on paper we can see the advantages of a twin set up vs a single turbo... something else that has been eating away at the back of my mind.

 

[danthman3]

well in my 3kgt they r in parallel
their is a front turbo for the front 3 cylinders in the V
and a back turbo for the back 3
the back turbo runs to the driver side mount ic and the front turbo goes to the passenger
then they meet up again at the tb area
i don't think this kind of set-up has any gains over a single turbo system except spool-up and convienience of mounting
its worth looking into tho

 

[OmegaGS-T]

ok forgive me but I read most of the first page and scroled through the next two... but just as an example... I had a few free mods done... open dp K&N and that stuff... 14b was going bad figured I'd pick up a 16G.... now with no other mods at 10 PSI my car made quite a bit more power than the 14B at 10 PSI.... don't have dyno's for comparison mostly just from racing a certain person... now spool up sucked ass with no supporting mods... but anyone my question is if 10 PSI is 10 PSI how did I get faster? also how would the turbo run cooler if the housing is the same size? if someone already answered all that just slap me I'm a little tired right now.

 

[Tevenor]

Ok I am closing this thread for 2 reasons.

1) I think everyone has had their say.

2) It's degenerated into post from people who can't read the rules, much less type using proper English and Grammar.

danthman3: Your next post better be a lot better example of the English language or it will be deleted in this forum.

On a side note, 3 periods are not necessary to emphasize your point. Neither is 2. Just 1.

 

[Tevenor]

I am reopening this thread at the request of a few DSMTuners members that are really looking to gain some knowledge. There is a lot of good conversation and discussion here. If your post does not meet the forum rules and ventures way the hell off topic, it will be deleted. Simple as that.

 

[Eclipsor16G]

This is a very amusing thread.

Some of you seem to be so confident in your flawed logic that you don't even bother to read the one post that made the most sense.

Tevenor knows what he's talking about and only used facts to back up his points. His first reply answered the poster's question and, in my opinion, should have been the last message in this thread.

IF YOU HAVE NOT DONE SO ALREADY, RE-READ TEVENOR'S FIRST REPLY. Do not read it if you just want to disagree with it. He is absolutely correct in every single point he made. Learn from him; do not attempt to contest basic (yes, basic) physics.

Now I'm just going to ramble and ramble and ramble:

CFM is what determines the power potential of a turbocharger. A 600 CFM turbo will not flow 600 cubic feet per minute all the time. It is simply a measurement of the turbos potential. It CAN flow 600 CFM if the system allows it to do so. A datalogger is very informative tool. Use one and learn - it will clear up much of the confusion that's apparently rampant throughout this thread.

Tevenor used examples to help you all understand the concepts he was discussing. The 2 liter coke bottle example was VERY easy to understand. Let me try to explain, one last time, how the ideal gas law applies to our engine and turbo.

First of all, a turbocharger "knows" nothing. It's not trying to fill any certain amount of space, it's not trying to flow a certain CFM of air. It's simply an air compressor. This is essential to understanding all of this.

Exhaust gases spin an exhaust turbine, which in turn spins the compressor wheel. This compressor wheel SUCKS air through the air filter, through the MAS, and into the compressor housing of the turbo. One can determine the amount of flow at any given time by converting the reading from the MAS (measured in Hz) to CFM (cubic feet per minute). So up to this point, everyone should understand that CFM is simply the rate of air flow through our MAS.

When you floor it and your turbo spools up to max boost, the wastegate is opened to divert air around the exhaust turbine of the turbo. If this did not occur, the turbo would spool up until something brakes.

So after that air is sucked into the compressor housing, it is compressed (obviously). The air is shoved into the space available between the compressor housing and the intake valves. Hypothetically speaking, let's say all the intake valves stayed closed. The turbo could produce huge amounts of pressure because none of the compressed air is leaving the system. This is not how it works, but it's good to understand this concept.

Let's talk for one second about a naturally aspirated engine. The piston moves down, sucking air through the intake valve into the cylinder. This is how a naturally aspirated engine "breathes." There is no pressure differential between the intake manifold and the cylinder, so air would NOT flow into the cylinder unless the piston sucks it in.

So now we have the turbocharger spinning at a relatively consistant rate and sucking in a certain CFM of air. This is all goverened by the boost controller and wastegate. As the engine revs higher, intake valves are opening faster and faster and more air is being taken from the intake tract and shoved into the cylinders. The turbocharger needs to work harder to maintain the specified boost levels. A 14B may be able to provide 25 psi of pressure at 3K RPMs, but once you near redline and the engine is breathing heavily, the 14B will not be able to keep up. It will not be able to FLOW the amount of air necessary to keep the intake tract pressurized. Furthermore, once you get close to a turbo's maximum flow rating, its efficiency drops and the compressed air becomes hotter.

Enough of the illustrations. Back to the ideal gas law. PV=NRT We know that pressure is constant in the equation (we're running a set 20 psi), and we know that V is constant (intake pipes do not expand or contract). We also know that R is constant (it always is). The last two variables are N and T. T is temperature, and N can be thought of as the density of air molecules in the intake tract. If the temperature is lowered (on the right side of the equation), then N *must* increase (basic algebra). This means that at a certain pressure, in a constant volume, lower temps allow for (REQUIRE) more air molecules to be packed into that volume.

Heat is generated by all turbochargers, but some turbochargers are more efficient than others. Efficiency is what determines the amount of heat generated by compressing the air molecules.

To sum this all up, a larger turbo will not reach its max flow rate nearly as easily as a smaller turbo will. In turn, it will be running more efficiently and the compressed air will be cooler and thus more dense.

I can't type anymore - my brain has turned to mush. I probably made some mistakes, but I can't re-read this whole thing right now. I hope I made some sense.

Chris

 

[Goblin]

Word

 

[babell2]

I am amazed! I didn’t know we had so many engineers and physicists on the list. In basic simple terms 15 psi from a 14B or a 20G will be the same in the same installation. When compressing ambient air to 15 psi the heat rise should be the same. The 14B just needs to work harder for it. The only way to improve 15 psi is to improving the cooling of the air charge to make 15 psi denser (the air density theory, colder denser, higher pressure denser) 15 psi is 15 psi until you can change the temp.
Rember folks "the same instalation" yes the 14B will run out of steam sooner when the VE of the engine outruns the ability of the 14B to keep up.

 

[booster]

there is a real lot of confusing stuff going on here. and im starting to get confused myself.
if you take a turbo which flows 1000000 cfm and try to stick it on a 4g63 and run it at 15 psi your engine cannot flow 1000000 cfm and if it could the psi would be um, half a million what im trying to get at is if you flow 300 cfm at 15 psi how can you flow 600 cfm at 15 psi. you really cant unless you change the way the head flows the air. right?

 

[babell2]

Originally posted by booster
there is a real lot of confusing stuff going on here. and im starting to get confused myself.
if you take a turbo which flows 1000000 cfm and try to stick it on a 4g63 and run it at 15 psi your engine cannot flow 1000000 cfm and if it could the psi would be um, half a million what im trying to get at is if you flow 300 cfm at 15 psi how can you flow 600 cfm at 15 psi. you really cant unless you change the way the head flows the air. right?

You are correct if the head flows 300cfm at 15psi thats all it will flow at 15 psi regardless of how much air the turbo can produce. The engine is in all basics an air pump. By increasing the boost say 20psi you can get increased volume through the engine but 15 psi=15 psi

 

[Ace140]

Ok... failing to consider temps and compressor effiecenty into the picture(say they are equal for both turbo setups), The difference is this: It takes 14 psi to create the same airflow(readower) that a turbo twice the size would make at 14 psi.

Thats say, thereticly, that a T-25 is half the size of a T-4. So, if you are getting 14psi of boost with say 300cfm on the T-25, the T-4 would flow 300cfm at 7psi, and 600cfm at 14psi. Airflow creates horsepower, not boost.

This takes into account only max airflow, not the spool charactoritics, but its a pretty good summary for WHY bigger turbos = more power.



And ignore my spelling, im a wee bit intoxicated.

 

[dsmtsiawd]

psi is psi.
like most people have been saying.
you can only flow as much as your head, valves, exhuast,IC ect. period
bigger turbo= more power, most cases yes, but becuase of lower air intake temps. period. like people have been saying
thats really all there is to it. of chours there is advanced equations. but that is the jist of it.

adam

 

[pneumo]

This may be a little off topic, but I'd like to address one of the reasons many people "think" that a bigger turbo makes more power at the same psi. As OmegaGS-T asks a few posts up, why did his 16g make more power at 10 psi than his old, fading 14g? Any new turbo makes more power when the old turbo is going out. Sure, most old turbos still spin nicely when you take them off the car and play with them, but when it comes to making boost, they eat up too much power. You replaced a blown turbo with a new turbo, that's all.
Another one I hear goes something like," My new Superfreak turbo makes way more power at 15 psi than my T-25 did at 20!" I'd just like to point out that 1. that is way past the efficiency range of the T25, it's heating up the air tremendously, 2. it simply can't flow enough air to keep up with demand at higher rpm's, so pressure will drop off. 3. running that much boost will blow out the bearings quickly and possibly unnoticeably at first, see blown turbo comments above.
And then there are the misconceptions that seem to be repeated often enough that they gain credibility.
So there are reasons that putting on a big turbo makes more power at the "same" psi as the old turbo, but most reasons are due to other things besides the science of airflow.