Ok this might be dumb but if you have a small turbo pushing 20 lbs of boost what is the advantage of getting a bigger turbo that takes longer to spool up and pushes 20 lbs isn't the air volume the same??

 

No, larger turbo will move more air than a smaller one. Additionally, the larger turbo should be more efficient at the higher boost levels thus not heating the air as much as it compresses it.

 

so basicly it just keeps the air cooler. because 20 lbs is 20 lbs so its not the pressure it it the ease of moving the air?

 

As far as I understand it psi is just a measure of force. Larger turbos move more air volume which is measured in cfm. Also the k03 will spike at 20 and hold at a lesser amount. A larger turbo will let you hold higher boost.

 

ok im still a lil confused about the physics of this. if you pump air into the manifold with a larger inlet it will do it faster but if the manifold is at 20 psi forcing air into the engine and the smaller turbo forces the same amount at a slower rate is the engine not getting the same amount of air. because the pressure is the same because if the larger turbo is pushing more air the psi would be higher.

 

creeve has it well said in lamans terms.....i will let someone else explain the hot/cold side ratios and how it effects the flow. but the k03 with a proper tune just cant flow enough air to hold 20 psi through the rpm

 

the typical place to measure boost is right before the intake manifold.....if its 20 psi right before the intake manifold with the small turbo and its 20psi in the same spot with the larger turbo its the same amount of air flowing into the engine regardless of the size of the turbo.

 

20 is just a number so basicly the bigger turbo move more air at the same amount of pressure?? because im thinking of it this way say you take a bigger turbo and you are filling a ballon the larger turbo will fill the ballon till it pops faster. the smaller turbo will fill the same ballon at a slower rate but it will still pop at the same point. so if your manifold has 20 psi in it that means the air density will be the same no matter what because the volume of air will be the same.. and would the lil bit of time it took for the bigger turbo to get up to pressure not be worth is for the time it takes to spool up?

 

I just started reading a primer on turbo chargers. Althought I can't answer your question specifically, I can tell you that a proper system is designed with a calculator, not a scale ("the bigger the better"). Your question is only taking into consideration one of many variables that all have to be looked at in the design of a system and the sizing of the turbo.

 

before you start upgrading your turbo, PLEASE read up online about how to read compressor maps and what they mean. That will answer all of your questions.

in short, psi does not equal air flow.

 

Unless the laws of thermodynamics have changed in the 35 years since I got my engineering degree, if the manifold pressure is at a constant 20 lbs, you are moving the identical amount of air through the system regardless of what is creating that prssure upstream. This, of course, is assuming a constant temperature as well. However, as indicated previously, a smaller turbo will have a greater tendency to heat the air stream, reducing air density. Hence less air, even at the same pressure. Best bet: forget about a larger turbo and put in one of those intercoolers that are 3-4 times larger than stock.

 

You are ignoring air density that is a function of air temperature.

 

bingo... more room to compress, less heat absorbed. if you've got really hot air and run it through an intercooler, you're not gaining any oxygen molecules, you're just lowering the temp of the intake air.

If you upgrade the size of your turbo, you generate less heat in the compression stage, and will cool to roughly the same temperature as with the smaller turbo due to the intercooler (a larger intercooler will be needed), you will have a lot more oxygen in that air.

It's a game. You want a bigger turbo so there's more room to compress. Too big of a turbo and you'll be so laggy, it will seem like you don't have a turbo for the first half of your usable rpm range.

at least this is what i am gathering after a few hours of reading of the past month or so.

 

so i was understanding correctly it is the same amount of air but the bigger turbo pushes colder air so there for it is more dense thus holding more o2 and creating more power. the smaller turbo put through an intercooler can produce the same temp so it will be just as dense but there will be less of an o2 in the air because the intercooler cant add o2 thanks that answered my question.

ill just put a nos fogger pre bigger intercooler that will get you air temp and o2 up hah just kidding

 

Are you kidding here?

 

And consequently lowering the pressuring at the manifold unless you've got something to drive more air into the system .

 

don't forget the effect that temp has on air density. Same pressure + higher temp = fewer air molecules

 

No: despite the fact that the larger turbo has a greater air handling capacity, tthe intercooler on the MINI appears to be undersized for the KO3 turbo**. Aftermarket ICs about 3 times larger than stock are showing some great hp gains (15-20). A KO4 turbo could void the warranty. The IC is unlikely to.

**Explanation: The IC will reduce the downstream temperature of the charge as well as the dowbstream pressure, allowing the turbo to spool faster (more air)for an equivalent amount of exhaust flow that is driving the turbo.

 

Here's a good technical article about turbo sizing, it is focused on 86-87 Turbo Buicks, but it gets the point across (these guys have been perfecting the theory through trial and error for the better part of the last two decades):
http://www.gnttype.org/techarea/turbo/turboflow.html

Turbos differ in efficiency, or the amount of energy transferred to compressing the charge vs. the amount of energy wasted by creating heat due to friction in the bearings. Other factors, such as the size/shape/angle of the wheel's blades on both the compressor side and the exhaust side effect overall performance.

Keep in mind that as you increase the size of the intercooler (3-4 fold) you are in essence tripling (or quadrupling) the volume of air that has to be pressurized, thus increasing lag. A large intercooler would be ideal for a system with a large turbo to flow a high CFM at a lower temperature which will quickly pressurize the system.

Just my $0.02

 

ok thx i got what i needed to hear this thread is no longer needed

 

All true.

 

That is true, but also keep in mind many of us folks down here need larger intercoolers because of heat-soaks we experience down here in the southern states.

 

The other issue is that ICs can have 2-3 times the amount of heatX surface without having 2-3 times the internal volume. Therefore spool up (or rather boost up) time does not increase 2-3 times.

 

Neither really matter, I've never seen a car lag much from the install of a decent intercooler. Its nearly imperceptible, and your car should be running cooler so it won't matter. This is a really nice theory thread but in reality its just that-

Some references...
http://forums.vwvortex.com/zerothread?id=3896131
Don't worry about a bigger intercooler, and a turbo is all about volume. You got a huge turbo like the one in my thread @ 20psi, it'll push a lot more air volume and you'll make power. Soon I'll have some logs to show what I'm talking about on the mini

 

Wait, so adding this giant ALTA intercooler is supposed to make more power than if I added a larger turbo? I'm sorry, but that power just isn't there. Maybe ALTA's intercooler isn't big enough?