• AFM Info

    Well the two possible limiting factors of an AFM are its physical flow properties and its max flow reading.

    When upgrading to a free flowing intake the AFM is usually one of most obvious restrictions or narrow points, so it can be useful to upgrade to a larger diameter one. However you have to really weigh up whether this is enough of a restriction to be costing power... and in the case of DETs you have to look at the diameter of the inducer on the turbo, which is generally pretty small on factory turbos...

    AFMs have an output voltage of between 0-5 volts, each indicating a specific cfm (air flow as cubic feet/minute). So every AFM has a maximum cfm it can read, which is when it outputs 5V. Everything over this amount cannot be communicated to the ECU so will be a hard power limit. For this reason, when chasing big power many people upgrade to Z32 AFMs as they have a comparatively high max reading. However, since the voltage range is still only 0-5V and its measuring a bigger cfm range (0 - max), its obviously going to have less resolution, ie, bigger gaps between cfm readings for the same voltage intervals, which I believe can negatively effect tuning resolution.

    Below is a rough guide to power values & diameters for Nissan AFMs:

    ------ ---- OD ------WKW
    SR20 ----- 65 ------ 200
    RB20/25 - 80 ------ 226
    Z32 -------80 ------ 255
    Q45 ------ 90 ------ 302


    As mentioned, for upgrading the AFM, you'll need to either get an aftermarket ECU or remap.


    Attachment 785


    Wiring up the Z32 AFM to the SR20DET Loom

    As seen above the afms all have different plugs. When wiring up a Z32 afm to an SR20 it is best to buy a new plug and do some fresh wiring. I purchased a new bosch plug from Unigroup Engineering for $30. It features a nice reatining spring clip that is much easier to use than the factory clip setup.

    The SR20 loom has only three wires leading to the afm, one black, one white and one one black/white. The Z32 plug is marked ABCDEF, from left to right. The wiring goes as follows:

    A - nothing

    B - white wire from SR20 afm wiring

    C - ground (just a normal grounding connection to somewhere on the body) NOTE: Didn't end up needed it but do it just to be safe.

    D - black wire from SR20 afm wiring

    E - black/white wire from SR20 afm wiring

    F - nothing

    I wired in the two lgs in parallel so that I could make a convenient change back to factory if need be. Simply strip back the insulation on the wiring, atwist and solder on the new wiring and reinsulate.: