[Diy_efi] Found the Speed-Density Equation

Thu Jun 20 14:19:30 GMT 2002

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Speed-Density assumes that the pressure in the cyl equals manifold pressure 
and that the percentage of o2 in the air is constant. The Ideal Gas equation 
of PV=nRT solved is for n (the number of mols of air), n=PV/RT is then 
solved. With constant pressure differential across the injectors, n becomes 
directly proportional to pulse width.
P is cyl pressure, measured by the MAP sensor. V is the effective cyl volume 
which varies with speed (and maybe load too-Does anyone know?) (the high 
torque point is the point of peak volumetric efficiency). R is a constant to 
correct for the system units used. T is absolute temperature.
So, inj pulse width is proportional to MAP x Volumetric Eff / Abs temp. Not 
too difficult to solve in real-time!
I'm planning to correct volumetric eff in 10, 600RPM bands from 600 to 6000 
RPM. Is that OK?
It looks like the TPS is only for "housekeeping" (Accel enrichment, starting, 
WOT & Idle detection, etc.) Does anyone know if thats correct?
Jim Grant  

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<HTML>Speed-Density assumes that the pressure in the cyl equals manifold pressure and that the percentage of o2 in the air is constant. The Ideal Gas equation of PV=nRT solved is for n (the number of mols of air), n=PV/RT is then solved. With constant pressure differential across the injectors, n becomes directly proportional to pulse width. 
P is cyl pressure, measured by the MAP sensor. V is the effective cyl volume which varies with speed (and maybe load too-Does anyone know?) (the high torque point is the point of peak volumetric efficiency). R is a constant to correct for the system units used. T is absolute temperature. 
So, inj pulse width is proportional to MAP x Volumetric Eff / Abs temp. Not too difficult to solve in real-time! 
I'm planning to correct volumetric eff in 10, 600RPM bands from 600 to 6000 RPM. Is that OK? 
It looks like the TPS is only for "housekeeping" (Accel enrichment, starting, WOT &amp; Idle detection, etc.) Does anyone know if thats correct? 
Jim Grant&nbsp; </HTML>

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