Accel enrichment

[Clive Apps Techno-Logicals 416 510 0020]

> >
> > What is going on in terms of MAP, air flow velocity, pressure,
> > fuel vaporisation and VE?
> 
> MAP; I explained my observations.Air Flow Velocity; My observations lead
> me to think the air flow increases beyond the steady state for that
> throttle setting.  Pressure; Above what is needed at that steady state
> throttle setting.


this is not difficult to understand
when you first increase the the throttle opening there is a larger
vacuum under the plate than there would be at steady state at the
same plate opening

this will increase the flow over that opening for a short period of time
because carbs are non linear and take time to respond as burst of 
fule has to be added to the air column to allow the carb to correct for
the flow increase

on FI you will have to very briefly add enrichment to make up for 
what fuel air mix is already in the plenums/ ports ect. that would
other wise be slightly leaned out by the sudden introduction of more air
than would normally be flowing past the same throttle opening

als you will usually want more power while accelerating than cruising
at a similar throttle opening, riching up the mixture in an engine tuned
for emissions as they are today will help it make a little more power
while the power is required

this + all the other stuff listed below
and probably a whole bunch of other reasons as well
h
Clive 

> Fuel vaporisation; because the pressure rises, fuel may flash out of
> suspension adding to the requirement of more fuel.  However, Smokey
> Whatsisname put a plexiglass window in a manifold and observed rivers of
> fuel running down the manifold runners in one of his NASCAR engines at
> full throttle.  So, we talk about vaporization, but is what really
> happens?  Look down a GM TBI while it's idling.  You can see the fuel
> running off the throttle blades.  I'm sure it flashes to vapor after it
> passes into the low pressure region on the other side of the TBI.
> VE; at wide open throttle, the VE of an engine depends on the matching of
> the camshaft, intake, and exhaust designs and is RPM dependent.  Nothing
> new there.  Peter added the observation that the flow rate is a sine
> function for a butterfly throttle system.
> 
> >
> >
> > What algorithm are in use, and what do they depend on?
> 
> I haven't figured that out, yet.
> 
> >
> >
> > Any help greatly appreciated.
> 
> Have we helped you, any?
> 
> My suggestion is to mount a vacuum gage on a car and watch it's behavior
> under various throttle postitions and accelerations.
> 
> Joe Boucher
> '70 RS/SS Camaro  '81 TBI Suburban
> 
>