MAF

[Tom Sharpe]

Greg Hermann wrote:

> >>
> >> Sorry--spaced out showing the VE calc--so here it is:
> >>
> >> (7)  3.8 liters x 61 cubic inches/liter = 232 cubic inches
> >>
> >> (8) 232 cubic inches/revolution / 2 revolutions/cycle x 5300
> >> revolutions/minute = 614800 cubic inches/minute.
> >>
> >> (9) 614800 cubic inches/minute / 1728 cubic inches/cubic foot = 356 cubic
> >> feet/minute (theoretical swept intake volume)
> >>
> >> (10) 299.6 cfm/356 cfm = 84.2% VE (actual intake air volume/theoretical
> >> swept intake volume) ((3)/(9))
> >
> >except max VE occurs at ( or very near) max torque
> >not at the max flow rate of the injectors if porperly sized
> >real VE for this setup would be in the 95-100% range if the torque peak is in
> >the 3500 range
> >
> >also you are relating the VE to the size of the injectors
> >this really has nothing to do with it
> >just supplies a number that is the max VE that the FI could support
> >with these injectors
> >increasing size 17% or fuel pressure 35% would allow the same injector to
> >support 100% VE at your indicated 5300 RPM
> >
> >Clive
>
> All I was doing was calculating the VE for the particular operating
> conditions which were stated---170 gr./sec. @ 5300 RPM on a 3.8 liter  4
> stroke engine , as an example of how to do the calculation.
>
> Of COURSE maximum injector duty cycle % will occur at maximum VE (which
> occurs at maximum bmep, and at a lower engine speed, one which is fairly
> near the brake torque peak, if we are going to be truly rigorous about our
> semantics.) But the same calculation would apply had the data at that
> engine speed been given. Anyone who wanted to develop a VE vs. Rpm curve
> could do so by data logging the output from the MAF vs. RPM. Pretty simple
> thing to plug into a spread sheet from there. Could tell a person a whole
> lot about cam profiles----
>
> And YES, peak bmep DOES happen at a DIFFERENT engine speed from brake
> torque peak, because friction losses vary with engine speed also!
>
> Regards, Greg

Found a bugggg.......  At Maximum VE, Pulse width is at maximum, but, injector
duty cycle % continues to rise with RPM as long as VE drops less than RPM
increases. Max duty cycle will occur at or after max HP.  ( amount of fuel used
per time ).

Regards  Tom