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Thread: How To: Read Compressor Maps

  1. #201
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    Sound. That now makes sense to me! Was getting myself a bit confused over that

  2. #202
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    Supercharger map

    It's been a long debate about Rotrex SC efficiency and MAX boost for M54B25/B30 engines. Can anyone teach me how to read the chart for supercharger compressor on the example below, Rotrex C30-94?
    C30-94 flow chart.jpg

  3. #203
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    Its not even max boost, its RPM. Calculated from crank/sc pulley size.

  4. #204
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    I would say that C30-94 is way to small for a 3.0l engine ...
    please find attached a calculation for a 2.9 engine and the biggest Rotrex available - C38-81
    If you have any questions about how was calculated - feel free to ask
    Best, Bogdan
    Attached Images Attached Images
    ' 99 E36 316i Compact, 83kw

  5. #205
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    Here is a question I did not see answered. How do you read the maps if you are use two turbos? Would your values be halfed?
    Heres what I have and why I am asking, my current build up is a Small Block Chevy 383, getting two turbos, one running off of each exhaust bank. I'll be running a max of 15 psi, and according to the Airflow Chart Def made, at 2k I will need 25lbs min, and up to 6k I will need 77lb min with a PR of ~2.1. Also, this is with it running at 80% VE.
    So, for each turbo, the values I should be looking at will be 12.5lbs at 2k and 38.5lbs at 6k correct with a PR of ~1.5?
    Or would I half the boost, and calculate each turbo running at 8psi which did come up with different numbers.
    Also, I know a single turbo is more efficient, but this is the plan!

  6. #206
    Def's Avatar
    Def is offline Lead Disagreement Eng PE
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    Pressure Ratio will be the same(i.e. boost pressure is the same at each turbo outlet), but you are correct in that total flow is cut in half for 2 turbos. 80% VE is pretty conservative for a turbo engine with a favorable intake/exhaust pressure ratio and a reasonably sized cam. At least it is that way with most modern 4V/cylinder heads. SBC's tend to have a more narrow efficiency window due to packaging/head constraints, but I'd still think you could get it a bit better than 80% at 6k RPM.

    Twin turbos make a lot of sense for a V engine, so you'll get no arguments from me on your plan!

  7. #207
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    thanks for putting this together....gave me a good insight on how to read the maps....now i can go somewhere and work out how much power i want to make and what turbo to get
    - Chris
    Track my race car buildup here - http://forums.eurocca.net/showthread.php?t=30668



  8. #208
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    good stuff DEF!

  9. #209
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    Absolutely great info !! Thanks Def !

    and the spreadsheet is really the best !



    I guess it doesnt really matter for those of you who are running a turbo already , you can select a different sized one .......



    But it would be very interesting to see some of the new turbos maps(comp wheels) in comparison ....

    and then see when a bmw engine( not a 2.0 liter) will work with them

  10. #210
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    Thanks a lot Def, thats what I figured.
    I figured I would go conservative with my numbers so that way I will be less likely to be disappointed or expect too much out of the engine.
    I think I'll try to find a turbo that has a map that will fit in the ranges of 80% to 100% just to be safe, then afterwards play around with different turbos based on how well these work out.
    If you have any tips or pointers I would greatly appreciate.

  11. #211
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    First off sorry for asking what will is probably a stupid question. Reading the first post and looking at the lines you have drawn on the compressor maps. I understand the horizontal lines are drawn at the desired pressure ratio and that you started off on the x axis with the corrected flow given at 2000rpm in your spread sheet. What i don't get is how you calculate at what gradient the line goes from the x axis to your pressure ratio line? Is it related to the constant speed lines or calculated through the turbine maps?

  12. #212
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    Can Someone Email The latest version of the spreadsheet to me? (after the data uplink ban)
    Aetro4@gmail.com
    Thanks

  13. #213
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    very nice write up.

    Thanks!!!
    "If you can leave black marks from the time you exit a corner till the time you brake for the next turn, then you have enough horsepower." --Mark Donohue

  14. #214
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    milKt is offline ßMW///MµrÐêr§þðr†
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    Wtf

  15. #215
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    Sorry but i can't understand it......
    ......................

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