TURBO INFO [compressor maps, flow, volume etc.] - Page 3
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This is a discussion on TURBO INFO [compressor maps, flow, volume etc.] within the Engine Modifications forums, part of the Tech & Modifying & General Repairs category; complexx: Although your question is posed to djres4, I'll take a whack at it. correct me if I'm wrong, but ...

  1. #31
    Registered User hotrod's Avatar
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    Turbo's

    complexx:

    Although your question is posed to djres4, I'll take a whack at it.

    correct me if I'm wrong, but you can't be at more than one place on those maps at the same time right?
    Well the answer to that is sorta yes and no .

    Your correct at any given moment you can only be at one point on the map, but at any given boost (pressure ratio) you can be at many different points on the map.

    Look at the 13G compressor map for example at the 2.0 pressure ratio line. You see that if you draw a horizontal line across the map at the 2.0 pressure ratio it can flow anywhere from about 100 cfm at the surge line on the far left side to about 360 cfm on the far right side. This is an example of the fact that a turbocharger is a fixed pressure, variable volume compressor.

    You use the waste gate system to define a pressure ratio for the turbo to run at but it can flow a wide range of air flows at that pressure ratio.

    The obvious question is how do you determine the point on that line that corresponds to the turbo's true point of operation?

    That left right postion, is defined by the air flow demand of the engine the turbo is attached to, and the turbos inlet air temperature and pressure (which we will ignore for now).

    If you turn a 2.0L engine at 4000 rpm and it has a .85 VE it will try to ingest about 240 CFM or in this example, right about where the right side of the 75% effeciency island intersects the 2.0 PR line.

    Push the engine rpm up to 6000 rpm and now the engine wants to flow 360 cfm which is the maximum rated flow of the turbocharger. (at least at reasonable effeciencies).

    As you can see at the midrange rpms around 3000 - 4000 rpm the 13G is a highly effecient turbo that will easily support boost pressures over 14 psi. It hits a maximum practical flow of about 300 CFM about 25 psi with acceptable effeciency, when the engine hits about 5000 rpm. ----- Hmmm that sounds a lot like the rpm range the WRX hits maximum torque doesn't it

    If you have a boost controller that allows you to map boost pressure to engine rpm, or if you fiddle with a more basic boost controller so it hits peak boost at around the peak torque rpm of 4500 - 5500 the 13G will make you a very happy driver.

    I think the thing you need to keep in mind is the turbo is not an independent unit, it is part of a co-dependent system.

    You can't define the turbo's performance until you know something about the engine it will be used on and its breathing ability, tune and rpm range.

    Larry
    Last edited by hotrod; 08-11-2004 at 09:20 PM.
    13.239@102.85 -- 5800 ft altitude
    on the stock TD04L-13T turbo

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  3. #32
    Registered complexx's Avatar
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    .85 VE? whats that?
    Never stop learning.

  4. #33
    Registered User hotrod's Avatar
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    abreviations

    Sorry --- VE is the usual abreviation for Volumetric Effeciency. That is the percentage of the physical swept volume of the piston that actually gets pulled into the cylinder at a given rpm.

    In the above example, a 2.0L engine turning at 4000 rpm actually sweeps out a cylinder volume of 282.4 CFM (Cubic Feet per Minute). But due to mechanical and aerodynamic flow ineffeciencies most common engines seldom can actually move that much air. Most engines run at somewhere between 85 and 95 % VE over most of their rpm ranges.

    A small number of ultra high performance engines that have been optimizes for operation at a certain rpm, and actually exceed 100% VE slightly due to ram tuning on the intake and exhaust.

    Loss of VE at high rpm is why engines power output eventually drops off at high rpm. The power increase of more power strokes per minute gets overwhelmed by a drop in engine effeciency at high rpm.

    Larry
    13.239@102.85 -- 5800 ft altitude
    on the stock TD04L-13T turbo

  5. #34
    Registered complexx's Avatar
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    Ok. Thanks for the clarification. I think I need to sleep a little and then start trying to work out some calculations tomorrow after I find the equations . Thanks again.

    My long term goal is to be able to single handedly choose a turbo for my STi by calculation and not word of mouth. Can you suggest any other reading that will map this process out in further detail?
    Never stop learning.

  6. #35
    Registered complexx's Avatar
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    And for the love of god why can't we all just use metric?
    Never stop learning.

  7. #36
    Registered User hotrod's Avatar
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    sources

    You might want to look over these resources:

    http://forums.scoobytech.net/phpBB2/viewtopic.php?t=53

    I'd start with the --
    http://www.stealth316.com/2-primer.htm and other related links on that web site.

    Larry
    13.239@102.85 -- 5800 ft altitude
    on the stock TD04L-13T turbo

  8. #37
    Registered User perfusionista's Avatar
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    Quote Originally Posted by complexx
    And for the love of god why can't we all just use metric?
    because we can't let the Burmese and the Liberians take the lead in everything...

  9. #38
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    04 Java Black Pearl - Sleek Eye

    All you see is my license plate... SCOOBY-X

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    Patrick, you are a complete accident

  10. #39
    Moderator Donkey's Avatar
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    The stock turbo on the WRX is a TDO4L-13T,not the TDO4L-13G.The 13T flows about 30 more CFM.Unfortunatly almost impossible to find a compressor map for it.
    Last edited by Donkey; 04-30-2005 at 06:26 AM.

  11. #40
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    Yep so guys all work for nasa then right?
    My emotions, and how my car is currently running are somehow interconnected. I would hate to see how I would react if I totalled it!

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