MAF constant 1010048999...

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MAF constant 1010048999...

Postby ol boy » Mon Sep 25, 2017 9:32 pm

What does this number 1010048999 represent? Ive played with the known unit conversions and cant seem to get anything close. 2.54^3 x 1728 x 3600 is a 10x short. Maybe adding lbs/hr to ml/min.. I dont know. That cancels out the 3600 in one form or another. In the MAF math this constant get divided by engine displacement then by airdensity.

Just trying to wrap my brain around the MAF math.

Thanks Ryan
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Re: MAF constant 1010048999...

Postby whittlebeast » Mon Sep 25, 2017 9:38 pm

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Re: MAF constant 1010048999...

Postby ol boy » Mon Sep 25, 2017 9:42 pm

Yep, thats where i got that big number from. Something to do with cc.. Uhm.
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Re: MAF constant 1010048999...

Postby robs » Wed Sep 27, 2017 3:45 pm

Not an area I've looked at, but the code has this to say:

Code: Select all
        /* was 61840750 for CID */
        /* this factor is calculated as follows - only used to generate mafload
        by definition mafload = 101.35 kPa at 100% VE = 1013.5 units.
        Density of air at 20C and 101.35kPa = 1.2041 x 10^-3 g/cc
        airden factor = 100.0% at 20C = 1000 units
        mafload = ((MAFCoef / aircor) * maf) / rpm)
        at 100% VE, flow = size x rpm/120 x 1.2041 x 10^-3 x 100
        maf = 100 x flow  units
        The 120 is converting from rpm to cycles/sec on a 4 stroke
        MAFCoef = k / size

        So, 1013.5 = ((k/size / 1000) x 100 x flow) / rpm
            or k = 1.0135 x 10^6 x size x rpm x 120
                   ---------------------------------
                    100 x size x rpm x 1.2041 x 10^-3
          rpm, size drop out
            k = 1.0135 x 10^6 x 120 / (100 x 1.2041 x 10^-3)
                = 1010048999
  (not quite the same as Al's figure 1013569893L which appears to use air density as 1.200x10^-3
        */

which seems to explain it pretty well.

Have fun,

Rob.
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Re: MAF constant 1010048999...

Postby ol boy » Wed Sep 27, 2017 6:57 pm

Which file is that in? I looked through the msextra main.h
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Re: MAF constant 1010048999...

Postby robs » Wed Sep 27, 2017 9:23 pm

It's in ms2_extra_init.c

Easily turned up with "grep 1010048999 *.[ch]" in Linux, or in Cygwin under Windows.

Have fun,

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