ko3 vs ko4 17psi. whats faster?

[cvharps11]

So I bought my car with bw ko4s on giac stage 3- tune and all supporting mods. I see some cats with ko3s pushin like 21. I would think they'd spool faster and inherently be faster. Can anyone fill me in?

[2.7taudi]

They spool faster but run out of "breath" at higher RPMs.

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[LINDW4LL]

K04 car will be much faster.

Stock RS4 spikes 16psi and makes 380hp. Of course that's conservative stock tune too. Also at equal PSI the K04 is moving more air for two reasons. 1) K04 air is cooler, more dense. 2)Flows more air due to larger turbine wheel.

[CELison]

K04s will move more volume. X psi is not the same on all turbos.

[cvharps11]

If the air flow is more shouldn't the boost be higher?

[CELison]

If the air flow is more shouldn't the boost be higher?

Volume and pressure are two different things laddy.

[LINDW4LL]

K04s will move more volume. X psi is not the same on all turbos.

Questin, Jesse (or for anyone else). Assuming the intake temperatures are the same, both turbos are cramming the same air mass into the intake manifold at 10psi.

Now, aside from the temperature difference due to the increased efficiency of the K04, the main increase of power from a larger turbo is because more air is able to escape the engine on each stroke due to the increased turbine wheel size, correct? Thus allowing more air to be taken in even though the pressure at the TB is the same.

[cvharps11]

Help this young grass hopper understand

[sjmelling]

K03 manual car 17psi vs K04 TIP car on 15 psi. K03 car had intercoolers and exhaust. K04 car has stock intercoolers and stock exhaust. Start vid at 4:05 or so. Red car is K04 TIP, silver car is K03.

[airjawed]

K03 will make power earlier in the rev range but run out up top. K04 will make power a little later but won't run out of power at the top. That is the basic comparison between the two turbos. The term faster...not sure what that means to you. Does it mean 0-60....does it mean 1/4 mile....does it mean on a twisty track...does it mean racing from a roll?

[sjmelling]

K03 will make power earlier in the rev range but run out up top. K04 will make power a little later but won't run out of power at the top. That is the basic comparison between the two turbos. The term faster...not sure what that means to you. Does it mean 0-60....does it mean 1/4 mile....does it mean on a twisty track...does it mean racing from a roll?

Exactly. On the highway, K04 car will win every time. On an Auto-X course, K03 car will pull out of the tight corners better and post better times. I like my K04's much more than my K03's. The difference in spool is barely noticeable and the pull up top is MUCH better even on mild boost.

[Fourplay]

If the air flow is more shouldn't the boost be higher?

Think of two tubes with air flowing through them at the same rate. One tube has a larger diameter than the other. Which tube has a greater airflow? The bigger tube. Same thing with turbos. K04s are larger, so at the same psi, they flow more air than K03s (and hence make more power).

[cvharps11]

Ahh I get it now. Thanks guys.

[FlyboyS4]

Think of two tubes with air flowing through them at the same rate. One tube has a larger diameter than the other. Which tube has a greater airflow? The bigger tube. Same thing with turbos. K04s are larger, so at the same psi, they flow more air than K03s (and hence make more power).

What happens when that airflow has to pass through an intake manifold of the same volume in both cases, at the same pressure, same temperature, and same rpm?

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[MetalMan]

Think of two tubes with air flowing through them at the same rate. One tube has a larger diameter than the other. Which tube has a greater airflow?

Just a thought here... if the air is flowing at the same rate, then they have the same airflow. For the same volumetric air flow rate (units such as CFM), the smaller tube will have a higher air velocity and a larger pressure lss over the length of the tube compared to a larger tube.

Perhaps you mean "with air flowing through them at the same velocity"? Because then the larger tube will have a greater air flow rate. But then why does the air velocity need to be the same between two different size tubes?

The bigger tube. Same thing with turbos. K04s are larger, so at the same psi, they flow more air than K03s (and hence make more power).

Not the same comparison IMO. A fan impeller has a characteristic curve that is far more complex than the pressure drop due to diameter change of a tube.

I work with/design fans for my job, and I'm a mechanical engineer by degree. Just needed some clarification.

[slow ride]

Whats your point, why stop at the intake manifold? What about through the engine and into the exhaust path?

[airjawed]

From an ECU perspective it does not see what is happening at the turbo itself. So, even though K04 is larger and flowing more volume it doesn't care or see it that way. It sees the air mass going past the MAF sensor....then it sees the temperature and psi at the intake manifold.

ECU perspective:

K03- more psi earlier in rpm, less psi up top and more temps up top.

K04 - psi take a little longer to develop, psi stays up top and temps do not increase as much up top.

[Fourplay]

Just a thought here... if the air is flowing at the same rate, then they have the same airflow. For the same volumetric air flow rate (units such as CFM), the smaller tube will have a higher air velocity and a larger pressure lss over the length of the tube compared to a larger tube.

Perhaps you mean "with air flowing through them at the same velocity"? Because then the larger tube will have a greater air flow rate. But then why does the air velocity need to be the same between two different size tubes?



Not the same comparison IMO. A fan impeller has a characteristic curve that is far more complex than the pressure drop due to diameter change of a tube.

I work with/design fans for my job, and I'm a mechanical engineer by degree. Just needed some clarification.

Facepalm. It was a (gross) oversimplification because the guy wasn't understanding how one turbo could have a greater flow rate than the other at the same PSI.

That's great that you're an engineer. I'm also one. The point of my post was to educate someone who is not an engineer and was having trouble with the concept. We can get into compressor maps, impeller size/design, housing size and design, and other higher level stuff, but the purpose of my post was to provide understanding on an elementary level.

What happens when that airflow has to pass through an intake manifold of the same volume in both cases, at the same pressure, same temperature, and same rpm?

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Velocity increases? You're the one with the flowbench, you tell me.

[FlyboyS4]

Velocity increases? You're the one with the flowbench, you tell me.

If the conditions are as I posed then nothing happens, the K03 and K04 'flow' the same amount of air into the engine, the exhaust side causes any differences. But to be clear, there are rpm regions where a K03 cannot supply enough air to match the boost level that a K04 can reach and the scenario I gave can no longer exist.

[BITRBO]

Beyond the ridiculousness of the question, I can't believe so many of you tards actually fed the troll... And Fourplay, Flyboy: I swear you guys love to argue just for the sake of arguing

[Meow]

Questin, Jesse (or for anyone else). Assuming the intake temperatures are the same, both turbos are cramming the same air mass into the intake manifold at 10psi..

No. Not true. Mass flow and manifold pressure are not the same thing.

[Fourplay]

Beyond the ridiculousness of the question, I can't believe so many of you tards actually fed the troll... And Fourplay, Flyboy: I swear you guys love to argue just for the sake of arguing

Comes with the territory of being an engineer. Every engineer thinks they're right 100% of the time when speaking to non-technical people, haha.

[Monty23]

[rdcyclist]

^^LOL...

Here's the question I have about slapping K04s or larger turbos onto our mere S4 engines: The K04 turbo was originally on the RS4 which has larger airbox, MAF housing, hose, y-pipe, inlets, SMIC's, intake manifold and heads. So when we put these bigger turbos onto the little intake tracts of the S4 are we shortchanging the potential of the mod? I've read the results of many of these builds with K04s, F21s, etc and see bigger numbers pretty much across the board but if the S4 intake was designed by Audi for the K03 it would seem to me that ANY larger turbo would need the rest of the intake components to perform at full potential.

[Monty23]

^^^ performance/$ my friend.

[Meow]

Comes with the territory of being an engineer. Every engineer thinks they're right 100% of the time when speaking to non-technical people, haha.

[FlyboyS4]

Beyond the ridiculousness of the question, I can't believe so many of you tards actually fed the troll... And Fourplay, Flyboy: I swear you guys love to argue just for the sake of arguing

These threads would get pretty boring if we all agreed all of the time. I've yet to hear a convincing argument for the other viewpoint so I keep giving my opinion.

[BITRBO]

Comes with the territory of being an engineer. Every engineer thinks they're right 100% of the time when speaking to non-technical people, haha.

These threads would get pretty boring if we all agreed all of the time. I've yet to hear a convincing argument for the other viewpoint so I keep giving my opinion.

I see what you're both saying - it's just funny to see the usual suspects scrapping it out all the time

[FlyboyS4]

Also at equal PSI the K04 is moving more air for two reasons. 1) K04 air is cooler, more dense. 2)Flows more air due to larger turbine wheel.

Here's a K04 compressor map with red filled in the region where the K03 compressor map shows greater or equal compressor efficiency to a K04.



A blanket statement like K04 air is cooler is incorrect, it depends entirely upon where on the map the turbo is operating. At an airflow seen around 3500 rpm and 20 psi the K03 is operating at 70% efficiency while a K04 around 63%; it's unlikely the K04 is discharging cooler air at that point.

More correctly, at equal manifold pressure a K04 has the potential to flow more air if the engine rpm and VE can support the additional capacity, if not, such as at lower rpm's, the K04 will 'flow' the same amount of air as a K03.

Questin, Jesse (or for anyone else). Assuming the intake temperatures are the same, both turbos are cramming the same air mass into the intake manifold at 10psi.

Yes. Imagine filling a bicycle tire to 35 psi, if you add or subtract some air what happens to the pressure? You don't stuff more matter into a fixed volume at constant temperature and not alter the pressure in the container.

Now, aside from the temperature difference due to the increased efficiency of the K04, the main increase of power from a larger turbo is because more air is able to escape the engine on each stroke due to the increased turbine wheel size, correct? Thus allowing more air to be taken in even though the pressure at the TB is the same.

You're on the right track, except for the part about the increased efficiency of the K04, that depends upon the rpm you are evaluating at. Engine VE change due to the different turbines is probably the largest contributor so long as the K03 is operating in a region where the efficiency doesn't suffer.

[S4 00 2.7]

I must be going crazy, Fourplay I thought you were in law school? I just learned you are an engineer.

back to your regularly scheduled program...

[Fourplay]

I must be going crazy, Fourplay I thought you were in law school? I just learned you are an engineer.

back to your regularly scheduled program...

Undergrad was in engineering, got my J.D. last spring with a focus on IP law (patent stuff).