INPA Engine Roughness Test - anyone know exactly what it is?

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  1. INPA Engine Roughness Test - anyone know exactly what it is? 
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    apigram's Car Details
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    Does anyone know what the INPA engine roughness test actually measures?

    My results are as follows, but not sure how to interpret. I swapped coils around (from off zero cylinders to others), but limited change...

    Results: Car is E39 528is (M52 Single Vanos. NOT Nikasil Block)

    engine rougness when at 90.5oC.jpg

    Thank you anyone in the 'know' !
    Last edited by apigram; 04-10-2012 at 14:52. Reason: typo
     
     

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    ed323i's Car Details
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    It's a 4 year old topic, but I'd like to know too.. I'd reckon they use data from the knock sensors.. But there are only two of those..
    Perhaps also slight deviations in the timing (measuring the rotation of the flywheel).
    Perhaps also using oxygen sensor values, but again, only two sensor, so no cylinder-specific data..

    I also wasn't able to discern any valuable data looking at the figures (M52B25 323i E36, single vanos)..
    Anybody else who can shed some light on this?
     
     

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    OK.. I've already found it.
    Details can be found here: INPA roughness values .
    It measures the impact each explosion in each cylinder has on the rotation of the flywheel (the RPM). It only works when idling.
    If one cylinder is misfiring a lot or the compression is down a lot, you will see deviations, because that cylinder will not give the same "push" to the flywheel like the other cylinders do.

    If you look at the crank/flywheel with a very high speed camera, you would see that every explosion accelerates the crank/flywheel a little, and after the gases have expanded, it decelerates again (because of the engine friction and the compression strokes going on. Because of the 4/6/8/12 cylinders firing so quickly after each other, it seems to us as though the flywheel is rotating at a fixed pace, but in reality it's accelerating and decelerating all the time. By using the timing sensors on the flywheel (and cam?) the DME/ECU can measure the acceleration each power stroke of each cylinder has. If it's producing less acceleration than the other cylinders, you will see a negative value. If it is producing more acceleration, you'll see a positive value.

    Small deviations should be no concern. There are always small deviations between the cylinders w.r.t. compression.
    I would also think that the less balancing factors the engine has, the easier it would be to notice differences.. For example, I think the M52 has more balancing components than the M50. Also, a heavier flywheel will also balance out the rotation more than a light flywheel.
    Last edited by ed323i; 07-07-2016 at 11:33.
     
     

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