Injector Sizing: REALLY dumb question

[goflo at pacbell.net]

Well, [:) ... 3000 rpm works out to a 40 ms cycle - Lets say 280 deg 
of cam duration, so 40 * 280/720 ~ 15.5 ms.
Injection duration depends on mass of air ingested during the intake
event
and injector size  - Light load, streetable injectors, so maybe 3
millisecond 
injection event, just to pick a number. My thought would be to time the 
injection event to begin after the intake valve is well off its seat and
end
well before closing - Correlate piston velocity per degree of crank
rotation
to valve position to see what's going on... Varies according to cam, rod
length, and stroke. Obviously as rpm increases the time frame shrinks,
but I
think this scheme would aid in fighting the soggy bottom common to
aggressive
cams. The more turbulence the better, largely a function of port &
chamber
shape - The point of the above is to have the injection event when the
velocity 
into the cylinder is high, and to end it well before the intake valve
closes so 
that the inevitable reversion does'nt include part of the fuel charge.

Regards, Jack

BTW, I have some programs which crunch engine parameters and produce
tables
of the various relationships described above. Not QBASIC, unfortunately,
but
not that big a deal to port them if anyone's interested.

Zack wrote:
> 
>  Granted that when the
> injector on time gets short, total fuel delivered in the pulse will
> become more variable as the natural variability of open/close time
> has more and more effect.
>         My question is, independent of these considerations, what is the
> effect of duty cycle?  If during light cruising, the injector is only
> delivering fuel during, let's say, 20% of the intake valve's opening
> time, you have this packet of incredibly rich A/F mixture rushing
> into the cylinder followed by a big gulp of air that has basically no
> fuel in it at all.  Is mixing inside the cylinder turbulent enough to
> ensure an even distribution by the time of ignition or is the charge
> still stratified?
> 
> Z
> 
> > The root of the thing is that
> > minimum injector-on time for most injectors is somewhere between .001
> > and .002 second - Less gives erratic fuel delivery.