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Thread: How To: Read Compressor Maps

  1. #101
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    Hi,
    Can someone tell me if the calculator is also applicable with 4cyl engines, because I find different values of flowrates following Corcky Bell's formulas?
    Is this possible? I have a 4cyl M10 engine 1800cc with stock compression(9,5) and i want to use an KKK k14 turbocharger. As for the engine it will stay pretty stock thus I will use low boost (6psi) with bigger injectors, bigger throttlebody and probably megasquirt in the future.
    Thanks for any input.
    Tim

  2. #102
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    It is accurate with any IC engine(meaning your 4 cylinder is applicable). The result depends greatly on your assumed volumetric efficiency(85-90% is a pretty conservative - meaning high - estimate on the volumetric efficiency of a 4 valve head). This formula also doesn't really take into account that many ambient conditions, since it will really only change the result 1-2% - and that's not stastically valid for your known information.

    The mass flowrate calculator is only to give you a general idea of where your engine will be on the compressor map. It'll tell you real quick if a turbo is grossly too small, or way oversized - but won't tell you that at 5628 RPM you'll go from 72% to 70% adiabatic efficiency.

    Don't fall into the common mistake of thinking you can wildly guess yourself to a more accurate answer - it's better to just do a quick "off the cuff" calculation when you don't know all the variables involved and try to make it a bit conservative, knowing this is your "worst case scenario" and design for that.

  3. #103
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    OK thanks
    I have a little difficulty to convert the different terms in which things are considered: like lbs/min and cfm. Should I refer to the lbs/min values on your calculator instead of the cfm to determine the airflow rate on the graph for the specific turbo? Am i right that the cfm values are without PR correction?
    What is the conversion from lbs/min to m³/s because this is the term they use on my graph as flowrate? For us here in belgium it is difficult to deal with all those different terms.
    Thanks for the help
    Tim

  4. #104
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    Hey if you are considering a K14 you may want to look into a K04 sport - there are a lot of them out there that have been upgraded to ball-bearing and with better impellers. Since there are so may out there, they might have a better power to cost return on your investment. I.E there are a lot of 1.8T VWs that are making well over 300hp with that turbo. Just an FYI...

  5. #105
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    hmm sounds interesting, I will do a little search on this one thanks!

  6. #106
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    Since lots of people seem to be getting confused with units, bookmark this site, it rocks!

    www.onlineconversion.com

    It's got basically every unit you could ever want.


    As for the CFM values, those are PRE-turbo. As in how many CFM of atmospheric air the turbo is moving(the volumetric flowrate - i.e. what CFM measures - will drop post turbo due to the increase in pressure, but the massflowrate - i.e. lbs/min - will stay the same due to conservation of mass). m^3/s should be pre-turbo just like CFM.

  7. #107
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    any of you got a copy of a T67 map. thanks

  8. #108
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    There are a few maps on this page, couldn't really find anything specific for a T67 after a quick look - but Google is but a click away.

    http://www.rbracing-rsr.com/turbotech.html

  9. #109
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    Just out of curiousity, why do you use the flow @ 2k & 3k rpm to define whether you are over the surge limit of the turbo??

  10. #110
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    It's a good conservative estimate of when a turbo will start spooling IMO. Most turbos will spool after that, so take that in mind if it looks like your big turbo is close to the surge limit when you do this analysis. It'll probably spool so late it'll "sneak" in under the surge limit since the engine will accelerate past that RPM point before it fully spools.

    Trying to model how the compressor actually behaves as it spools is a major PITA, since there are so many factors you'd have to account for(wheel RPM, wheel acceleration, rapidly changing VE of the engine at the lower RPM range etc.) that again - it's just best to have a pretty simple, conservative system that makes some reasonable assumptions then take it for what its worth.

  11. #111
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    Thanks for that, I thought that might have been the case.

    So how would one make a reasonable assumption on when the turbo would spool up?? As this involves the other half of the turbo also, turbine size/housing!?!?!

  12. #112
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    Best bet on when you'll hit full boost with a given engine/transmission/car combo is to find others with a similar turbo to yours and ask them.

    In this case, getting a quick emperical data sample is much much easier than attempting to do the calculations that will then only get you "close" to the real answer. After looking at a few different turbos and how they behave on different sized engines you can really quickly look at some combos and usually get pretty close to when they'll hit full boost(in say 4th gear on a dynojet for a standardized load).

  13. #113
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    Thanks for the great informations about how to read c.maps.
    But i have some questions.

    1.What airflow has a E36 328i at 2000 RPM???

    2.Why are you looking at 2000 RPM?

  14. #114
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    1. Not sure, DL the airflow chart and it should tell you at whatever pressure you want.

    2. I think it's a good point to look at the engine at atmospheric pressure then draw a linear line to about 3000 RPM to check for surge. Most turbos that will make "reasonable" power on an engine won't surge on spool-up, so it's not a huge worry, just something to check for. If you know the turbo won't hit full boost anywhere near 3000 RPM, then you could always change this value. I find that it's a pretty conservative estimate for most engine/turbo combinations IMO.

  15. #115
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    Quote Originally Posted by rswtal
    Thanks for the great informations about how to read c.maps.
    But i have some questions.

    1.What airflow has a E36 328i at 2000 RPM???

    2.Why are you looking at 2000 RPM?
    Do you mean NA or boosted?

  16. #116
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    The pressure ratio at 2000 RPM unless you are using an absolutely tiny turbo will be relatively close to 1(i.e. atmospheric pressure).

  17. #117
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    Quote Originally Posted by EEEEeeee36
    Do you mean NA or boosted?
    NA i think.

    i will read a bit more and give reply.

  18. #118
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    Quote Originally Posted by rswtal
    NA i think.

    i will read a bit more and give reply.
    If you follow the directions in post #1 in this thread, you should have no problems. Def got it down to a tee... cheers.

  19. #119
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    How do you calculate VE and I also have a turbo noob question. What is Trim? Is it another term for A/R?

  20. #120
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    Quote Originally Posted by black318i
    How do you calculate VE and I also have a turbo noob question. What is Trim? Is it another term for A/R?
    You pretty much "guess" the VE of the engine, and it changes throughout the rev band(pretty much proportional to the torque curve).

    Trim refers to the ratio of the "large" side and "small" side of the wheels(both compressor and turbine wheels have a specific trim). Usually higher trim on the same major(large) diameter wheel will flow more.

  21. #121
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    Wow...I learned more in the past 5 pages of this thread the I did in 12 years of school. Its either the educational system that sucks are you guys that rock. Thanks for the info.
    If I started this thread feel free to troll, thread jack and be profane at your leisure.


    Free Automotive advice from people who know what they are doing, not a bunch of high schoolers on BF.c

    1999 ///M3, BMW individual PINK...Like your mothers taint..............lol@corvette owners


    Get it straight morons:
    Benz = Mercedes Benz
    Binz = Nickname given to me by my brothers

  22. #122
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    I had some time so I did some work on my airflow chart. As Jacob mentioned before turbos spool up and boost grows fairly exponentialy, to the power of 2. I re-made my Turbo Airflow/Spooling psi graph to reflect this. I tested it on a few compressor maps and it's pretty accurate!

    This chart isn't just specifically to determine if the turbo will work on your engine or not. Check it out; it can help you decide if the turbo will spool up quickly enough for you, and if will have the kind of driveability you are looking for. Turbos that have more of a 'stock' driveability or that will feel more like you are driving an NA car will be at full boost closer to 2000rpm; turbos that are at full boost at higher rpms will have a little more lag and it will feel more like you are driving a turbo-charged car. The more boost you run the harder it is to get away from that 'lag' feel, however playing with the chart with a few different turboes and their Compressor Map can help you compare them. I've also modified the chart itself and the instructions to make it easier to use.

    Jesse

    EDIT: I apologize, I wasn't aware that we can't attach zip files AT ALL! If somene would like it PM me and I'll email it to you. It's pretty cool!
    Last edited by EEEEeeee36; 12-02-2005 at 01:13 PM.

  23. #123
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    I like it! It's a pretty cool little spreadsheet, and it does seem pretty accurate to me based on my turbo's response in higher gears.

  24. #124
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    Quote Originally Posted by Def
    I like it! It's a pretty cool little spreadsheet, and it does seem pretty accurate to me based on my turbo's response in higher gears.
    Thanks! Yeah of course 4th and 5th will be feel like a more direct correlation to how the engine behaves. I thought about being able to account for varying VE, but holy crap would that be obsessive compulsive! Besides, you'd have to run a dyno to see how your torque curve was, check all of your stats, and then input them manually to find out...what? That the boost was a half-psi lower or higher at a certian RPM? No biggie anyways, it just to help show characteristics of different turbos.

    I wonder why you can't attach zip files anymore? Oh well, I'll just host it on my site and link to it in my sig. That will work better anyways.

  25. #125
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    problem. . .i cant download any of those spreadsheets


    is there a certain guideline you could base spool up on for changes in a/r. say something like for every ______ change in a/r, boost is delayed _____rpms?

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