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    Thread: Is 20PSI on K04 equal to 20PSI on GT28? i think no my friend thinks yes

    1. Member BlackA4stage3's Avatar
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      05-09-2012 07:05 PM #1
      ok so here is what happened. a few days a ago i saw another B6 A4 guy drive by me so i followed

      him and he pulled over and we talked about our cars for a little. he said that he had a K04 setup

      running 20PSI of boost. so blah blah blah later that day im talking to my friend about his car and i

      tell him yea he is running a K04 at 20PSI. so he says "so its basically as fast as your car". i drive a

      B6 A4 with a GT28 running 20PSI boost. so i say no my car would be faster because it is bigger

      running the same PSI. so he says 20PSI is 20PSI. we argued for a good 30 minutes and couldnt

      come to a conclusion. i figured since its 20PSI in a bigger turbo it would be moving more air. Can

      someone tell me if im an idiot or right or what????? ive searched google and couldnt find a clear

      explanation. please help!!!

    2. Banned SVTDanny's Avatar
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      05-09-2012 07:06 PM #2
      Bigger turbo will almost always give more power at the same boost. Bigger turbos flow more air, more efficiently.

    3. Member ThreadBomber's Avatar
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      05-09-2012 07:07 PM #3
      You should have just whipped your cacks out and the question would have been answered
      Teefy Buna

      Quote Originally Posted by Sump View Post
      I'm sure a lot of these guys went home after the carwash and played a little hans solo.

    4. Member stascom's Avatar
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      05-09-2012 07:09 PM #4
      More air would flow at the same pressure through a bigger outlet... Why is this so difficult?

      Quote Originally Posted by ThreadBomber View Post
      You should have just whipped your cacks out and the question would have been answered
      This.

    5. Member rsj0714's Avatar
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      05-09-2012 07:10 PM #5
      Quote Originally Posted by BlackA4stage3 View Post
      Can someone tell me if im an idiot or right or what????? :
      Possibly all of the above.

      Larger turbos have more capacity, it's pretty simple. If you own a turbo vehicle you should atleast understand the basics of it's operation.
      Quote Originally Posted by Dave Zero View Post
      Station wagons are for moms and Europe.

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      05-09-2012 07:11 PM #6
      Think of power as a function of air volume rather than boost pressure required to supply that volume.

      20 PSI pumped through a straw will not flow the same volume of air as 20 PSI pumped through a garden hose... unless you've got a REALLY big straw.

    7. Member Shomegrown's Avatar
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      05-09-2012 07:17 PM #7
      This is going to be one of those TCL threads where it's best to look the other way and pretend you were never here.

    8. Banned Fritz27's Avatar
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      05-09-2012 07:25 PM #8
      Quote Originally Posted by Shomegrown View Post
      This is going to be one of those TCL threads where it's best to look the other way and pretend you were never here.
      Yeah, I agree.


    9. Member 200HP4dr's Avatar
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      05-09-2012 07:25 PM #9
      Quote Originally Posted by nmap View Post
      Think of power as a function of air volume rather than boost pressure required to supply that volume.

      20 PSI pumped through a straw will not flow the same volume of air as 20 PSI pumped through a garden hose... unless you've got a REALLY big straw.
      This. There are also other factors to consider, like the straw size, not only the ins and outs of the turbo, but the size of the intercooler piping, intercooler etc. The larger that piping is (assuming the bends are equal) the more air can get through at any given PSI. So, yeah, the post I quoted....

      Chris
      | 2015 Chevy Sonic | 2010 Dodge Grand Caravan | 1990 Ford F-150 | 2014 Prius | 1981 Datsun 280zx | 1965 Buick Riviera |

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      05-09-2012 07:26 PM #10
      Learn how to read turbo maps and answer your own question.

    11. Member Spiller337's Avatar
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      05-09-2012 07:33 PM #11
      With his logic, what would be the point of upgrading a turbo then?
      Quote Originally Posted by Ernie McCracken View Post
      Something something haters something YOLO, etc.
      @Spiller337

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      05-09-2012 07:35 PM #12
      You need to get smarter friends.

    13. 05-09-2012 07:47 PM #13
      Pressure and volume are 2 different things...


    14. Member taymk2's Avatar
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      05-09-2012 07:48 PM #14
      Quote Originally Posted by unintended acceleration View Post
      You need to get smarter friends.
      Lol

    15. Member Shomegrown's Avatar
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      05-09-2012 07:51 PM #15
      OK, the answers here are mostly right, but for the mostly wrong reasons!

      To understand, you need to look at the basics - what is boost?

      Positive boost pressure occurs because there is more air being forced through the engine than the engine can ingest using its own volumetric efficiency.

      Changing to a larger turbo does not have a significant impact on VE or the volume of your intake system, nor is it the most restrictive part of the intake (that's the throttle) so the "blowing through a straw" analogy is way off base. It doesn't apply at all.

      The reason larger turbos usually make more power for the same relative boost level is twofold:

      1.) Compressor wheel efficiency leading to lower IAT
      2.) Lower TIP (turbine inlet pressure or less exhaust restriction)

      What this means is if the IAT is the same and the exhaust backpressure is the same, then 20 psi on turbo X will absolutely equal 20 psi on turbo Y even if the turbos are sized differently.

      Now, both factors 1 and 2 can be controlled outside of turbo size. Let's pretend...

      Car # 1 has the smaller K04 but open dump pipes and a huge FMIC with meth injection

      Car # 2 has the larger GT28 but smaller intercooler and a quiet exhaust with cats

      Under those conditions, it would be possible that the Car #1 performs better at 20 psi than Car #2.

      Long story short, boost pressure is restriction in the engine, not the turbo. So 20 psi = 20 psi unless other properties are changed (VE, IAT, TIP, etc).

      So who's not going to read the thread and be the next to post the straw/garden hose analogy?

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      05-09-2012 07:54 PM #16
      The bigger turbo is capable of pumping more air at higher pressure than a smaller turbo. If the engine management is actuating the waste gate of both a bigger turbo and smaller turbo to keep the pressure in the intake manifold the same for the same throttle position and engine speed, then the power output of the engine will be the same despite the turbo size. The bigger turbo simply has more potential that is being wasted. In fact, the bigger turbo may be worse due to slightly higher turbo lag.

      If you take the smaller turbo and push it near the edge of it's design limits, the charge temperature will probably be higher, reducing engine performance. This situation is probably not terribly likely with a stock setup. In a car that's running higher boost pressure than designed, it can happen.

      It's likely a smaller turbo will hit the limit of it's air flow capability if it's too small, causing a drop in intake manifold pressure at higher engine speeds. So, in this case the bigger turbo is better. It's also not running at the same "PSI." The air flow is not high enough to maintain the pressure.

      If one of the setups is faster, it's probably because the slower car had a turbo that couldn't maintain intake manifold pressure when the engine gets closer to red line.

    17. Member Shomegrown's Avatar
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      05-09-2012 07:56 PM #17
      Quote Originally Posted by Brad2021hk View Post
      If the engine management is actuating the waste gate of both a bigger turbo and smaller turbo to keep the pressure in the intake manifold the same for the same throttle position and engine speed, then the power output of the engine will be the same despite the turbo size.
      Correct, but only if you assume intake air temps and engine volumetric efficiency is the same between both setups.

    18. Member abawp's Avatar
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      05-09-2012 07:59 PM #18
      Quote Originally Posted by Shomegrown View Post
      So who's not going to read the thread and be the next to post the straw/garden hose analogy?
      I'll just sit back and wait until someone tries to "correct" you
      Quote Originally Posted by Lwize View Post
      What, none of you watch reruns on TV?
      Quote Originally Posted by NPH View Post
      I don't know about you but, I get angry and shout "IB4TL" when one comes on.

    19. Senior Member JettaGT8V80's Avatar
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      05-09-2012 07:59 PM #19
      no

    20. Member BlackA4stage3's Avatar
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      05-09-2012 08:04 PM #20
      thanks for the comments guys. i always thought i was right but he made me second guess myself causing this thread lol. i will be sending him a link to this thread so say hi to him. his name is rusty and he drives a g35 coupe fully bolted

    21. Member 302W's Avatar
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      05-09-2012 08:07 PM #21
      Is the reason that IAT is lower with a larger turbo at the same PSI due to less air turbulence with a bigger inlet?
      Quote Originally Posted by Dave Zero View Post
      1988 is not an 80's car, it's an early 90s car but whatever.

    22. Member VWturbonium's Avatar
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      05-09-2012 08:24 PM #22
      Basically to expand upon what Shomegrown said, two differently sized turbos (lets assume similar compressor and turbine designs just different sizes) *can* make the same power at the same boost, it is IN SPITE of the size difference. The bigger compressor will generate less heat for a given pressure, and arguably even more important is the fact that the bigger turbine side will have a lower Exhaust or Turbine pressure ratio (lower ratio=better Volumetric Efficiency).

      On otherwise identical physical setups, even if you work to get IAT's on the smaller turbo down the bigger turbo will more power because of the hot-side still allowing greater VE.

    23. Member konigwheels's Avatar
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      05-09-2012 08:31 PM #23
      Quote Originally Posted by BlackA4stage3 View Post
      his name is rusty and he drives a g35 coupe fully bolted
      There's the problem. G35 with bolt ons, he should know the VQ doesnt do anything with simple mods. I'm totally assuming and kind of being an ass, but he probably got 10whp for $2000.

    24. Member BlackA4stage3's Avatar
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      05-09-2012 08:55 PM #24
      Quote Originally Posted by konigwheels View Post
      There's the problem. G35 with bolt ons, he should know the VQ doesnt do anything with simple mods. I'm totally assuming and kind of being an ass, but he probably got 10whp for $2000.
      he beats my avant with a gt28. he has put a lot of money in it but it looks great and sounds great and handles very well, so id say money well spent. plus NA means no turbo heart ache like us audi guys have sometime lol

    25. 05-09-2012 09:02 PM #25
      Yes, more capacity, but the same amount of air flowing through two different size tubes (turbos) will produce different pressures. Less flow through a smaller opening will produce more flow through a larger opening.

      The equation escapes me at the moment, I have not had physics for over 20 years. But this is straightforward physics. Your statement is suspect.

      Quote Originally Posted by rsj0714 View Post
      Possibly all of the above.

      Larger turbos have more capacity, it's pretty simple. If you own a turbo vehicle you should atleast understand the basics of it's operation.

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