Selin Dual Intake

Discussion in 'Technical' started by SrAfciGeR, Dec 30, 2016.

  1. SrAfciGeR

    SrAfciGeR Member

    According to this article

    Selin dual intake adds two MAF voltages together and then added voltage is divided in half. (later ECU needs to be reprogrammed so it can scale double amount of air "2x MAF" in the range 0-5V which are now combined and divided in half averaging the result in any given time).

    Schematic should look something like image below:

    Simple device of this type should cost few bucks only... not $500 :)
  2. JamainexD

    JamainexD Member

    If you can make these, and sell these to us on the forum i'm sure you will have plenty of buyers lined up.
  3. brisz

    brisz Well-Known Member

    Can you fix the image so we can see what it is ?
  4. SrAfciGeR

    SrAfciGeR Member

    I just gave you schematic diagram.
    This is more like DIY cut/solder jobbie..

    You will need
    6x 100kΩ resistors $2
    1x LM107 $25
    1x PCB Panel $1
    Few pcs of wire to connect it all together

    I could put PCB together for you but I would need to source appropriate connectors for plug and play type scenario...
    Those connectors would cost the more then what this thing is worth...
    1x MAF Male connector would be harder to source...
  5. SrAfciGeR

    SrAfciGeR Member

    First image looks small for some reason... try this
  6. syntax_X

    syntax_X Zed Head

    If its that easy why don't you seriously make a few. Send them out for testing.

    3 versions later and a shit fight with RFI you might have something worth using.

  7. Fists

    Fists Well-Known Member

    The description on SZ is pretty hand wavey. The airflow:voltage curve is logarithmic so if you just add/halve the voltages you'll be way off. Need to take each voltage, convert it to the air value, add or average the air values, then output the appropriate voltage.
  8. zx299

    zx299 Well-Known Member

    Correct ......

    Your diagram is of a summing amplifier, which just adds the two voltages.

    You need to add the two Airflows, not the two voltages.
  9. Veem

    Veem New Member

    I don't understand this. Isn't the voltage output of the meter representative of the airflow?

    Regardles, $25 for an opamp seems steep to me. Why not use a MCU like an attiny13 to measure the voltages, do the calc, and output your average. Seems easier to me, and lets you screw around with your formula.
  10. SrAfciGeR

    SrAfciGeR Member

    I don't know how to say this so you guys can understand but I will just go on and say it :)

    I can't convert voltage to airflow - ECU does it. and it does so using the "signal" or the "voltage value" that comes of the MAF sensor.

    So if you have a look at the image on the left (female plug pin-out) of the MAF sensor cable that goes in to ECU.

    A Not used
    B Voltage 0-5V signal to ECU
    C Ground
    D Ground
    E +12V
    F Not used

    B is your 0-5V signal that goes to the ECU (At this point there is no conversion) If you convert this to digital value, analog device awaiting for signal won't know what to read.

    And yes I add two voltages together and divide them by 2. that equals my average for two sensors.
  11. zx299

    zx299 Well-Known Member

    It is not linear .......

    Voltage Y = Airflow X, but Voltage Y/2 does NOT equal Airflow X/2

    Something MUST refer to a table to convert the 2 voltages to airflow values before adding the two airflows ......... then reconvert the result to voltage to send to the ecu.

    Your method will give you the average voltage of the two MAF sensors, it will NOT give you the average Airflow of the two MAFs
  12. SrAfciGeR

    SrAfciGeR Member

    You are welcome to present your design here.

    Price of opamp came of the ebay. Chinese suppliers will probably do it for less but I haven't went searching for cheaper components just yet...

    Regarding attiny13 haven't used them but if you finding it easier sketch it out for us.
  13. SrAfciGeR

    SrAfciGeR Member

    Yes you got it.

    I'm not looking for combined Airflow of the two MAFs at this point. Just the average value of the two.

    At this stage you go in to your Nistune and adjust MAF sensor for double Airflow this will get your Airflow's correction.
  14. Fists

    Fists Well-Known Member

    You would have to completely replace the AFM VQ table not just change a multiplier. You should also add a protection circuit in case one side of the intake tract gets blocked or disconnected as you could lean out/flood if the two MAFs are reading too far apart. Would also need the 'driveability/idle mod' used in dummy MAF set ups to get the right reading at idle and low throttle.

    Speaking of dummy maf, that is a far easier way to achieve a cheap twin intake, double air capacity set up. Connect MAF on one side, add driveability mod hose and double k value in nistune or ROM chip.

    The reason people go SELIN over dummy MAF is the safety and accuracy of having a proper converter in there.
  15. SrAfciGeR

    SrAfciGeR Member

    Why not use multiplier? What is the difference?
    Regarding protection circuit... If one side gets disconnected/faulty your MAF value will be (half of the average value) your engine will just stall as it will be too lean to do anything else...

    Happy New Year Guys

    I'm on my way to get myself blind tonight :)

    ZDUCTIV Active Member

    Averaging the AFM signals should be ok no? I can see the issues with adding the two voltages together because the exponential VQ table would cause issues.


    i.e. 2x 2V signals (approx 500 x 2 on y-axis) is not the same as a signal 1x 4v signal (~3300).

    However, averaging 2x 2v signals and passing the 2v signal to ECU then doubling the k-value to make the pulse-width twice as long should correspond the same air-fuel ratio?

    What am I missing zx299?

    Edit: Is it because if you're pulling air unevenly, i.e. averaging a 3V and a 2V signal, you're not pulling the same volume as air as 2 x 2.5V similar to the case for just adding them? So you'd be better off with a VQ table in your dual intake system, recording each MAF voltage, finding equivalent air flow, then passing the equivalent voltage back to the ECU? How different are the values that each MAF records in general usage. How much of a difference would these methods actually make?
  17. Fists

    Fists Well-Known Member

    Sorry, you're right, it would just need halving injector size. It would function like a dummy MAF system but with more confidence/less error when the two sides draw unevenly since you have two data points.

    Given the current price and exchange rate on a Selin translator plus an additional AFM it'd probably be better to just go to a standalone with a MAP sensor if you want things done properly and yours should be good enough for people that want a cheaper power boost and have a socketed or Nistuned ECU.
  18. lovmyzed

    lovmyzed Member

    some data.
    I looked into this a while ago, tried using an arduino (not fast enough btw).

    I then decided I was wasting my time any way, regardless, a table for any one so inclined:)

    voltage airflow (units???)
    0 0
    1 48
    480 48
    560 73
    640 104
    720 143
    800 190
    880 247
    960 319
    1040 405
    1120 509
    1200 638
    1280 784
    1360 947
    1440 1129
    1520 1299
    1600 1555
    1680 1804
    1760 2085
    1840 2397
    1920 2739
    2000 3111
    2080 3514
    2160 3968
    2240 4478
    2320 5027
    2400 5624
    2480 6273
    2560 6969
    2640 7710
    2720 8505
    2800 9351
    2880 10242
    2960 11189
    3040 12190
    3120 13249
    3200 14372
    3280 15556
    3360 16822
    3440 18141
    3520 19510
    3600 20953
    3680 22462
    3760 24050
    3840 25716
    3920 27472
    4000 29324
    4080 31267
    4160 33305
    4240 35432
    4320 37648
    4400 39977
    4480 42404
    4560 44923
    4640 47544
    4720 50268
    4800 53100
    4880 56040
    4960 59091
    5000 60620

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