TBI with TPI ecm???

[Bruce Plecan]

> Bruce Plecan wrote:
> > Dunno, how you can say "won't get any fuel".   The fuel is just being
spit
> > into a plenum anyway.  In theory firing them twice as often would be
better
> > for atomization, yes.  But, there is a whole lot of vaporization going
on
> > anyway.

> Lets assume the 2.5 L4 single injector TBI engine.  On this engine, the
> TBI feeds into a small common area which then immediately splits into
> four seperate runners to the ports.  Below is a diagram of when each
> cylinder is receiving air+fuel and when the TBI injector is firing.
> (View this in a fixed width font.)  Lets also assume a light throttle
> condition where the injector duty cycle is low.  Further, lets assume
> the ECM is firing the injector in middle of each intake stroke:

Well, for openers, if the injector pulse is referenced to spark, then the
injector will be firing at the beginning of the intake valve opening (but
immaterial, IMO).
Your also seem to be saying the fuel, and air will be changing directions
instantaneously, which just doesn't happen.  On a 4 cyl 4 stroke engine
there is one intake open all the time, and with that opening or closings of
others, so the plenum how ever small is like a tornado on the inside (for
lack of a better definition).  The fuel is being smeared around the walls
from the centri. force of this, and from gravity, some falls on to the
floor.  While yes some is in suspension, Lots of it is just waiting around
to be vaporized so it can be inhaled by the engine.   If fuel control and
the related porting was in response to instantaneous flow changes then
porting would be really easy to do.  Porting to get airflow right is
relatively easy, it's getting the fuel even that is the challenge (and why
port is better then TBI for some applications).
Bruce


>
> 1111111111111111111111__________________________________________________
> __________________3333333333333333333333________________________________
> ____________________________________4444444444444444444444______________
> 2222__________________________________________________222222222222222222
> _______Fuel______________Fuel______________Fuel______________Fuel_______
>
> >From the above diagram, each squirt of fuel should be immediately swept
> toward a different cylinder.  The runners to the non-intake cylinders
> should have little or no air flow, hence they won't get the majority of
> the fuel.  Now lets look at a diagram for a batch fired port injected
four:
>
> 1111111111111111111111__________________________________________________
> __________________3333333333333333333333________________________________
> ____________________________________4444444444444444444444______________
> 2222__________________________________________________222222222222222222
> FuelFuel____________________________FuelFuel____________________________
>
> Because of the port injection, each cylinder gets the same amount of
> fuel although the timing is different.  For cylinders 1 and 4, half of
> the fuel waits around on the intake valve and the rest is injected
> during the intake stroke.  Cylinders 2 and 3 have almost all the fuel
> waiting on the valve.
>
> Now consider what happens when a TBI injector is fired this way.  Most
> of the first injection goes to cylinder 1, with a small portion getting
> into cylinder 2.  Similarly, most of the second squirt goes to cylinder
> 4.  Thus, 1 and 4 run rich, while 2 and 3 are lean.  Now lets open the
> throttle causing a larger duty cycle:
>
> 1111111111111111111111__________________________________________________
> __________________3333333333333333333333________________________________
> ____________________________________4444444444444444444444______________
> 2222__________________________________________________222222222222222222
> FuelFuelFuelFuel____________________FuelFuelFuelFuel____________________
>
> In this case, all the extra fuel goes to 1 and 4 making them even
> richer.  Meanwhile, 2 and 3 are relatively even leaner.  Now lets back
> off the original duty cycle and assume the ECM is firing the injector
> only once per every other crank revolution:
>
> 1111111111111111111111__________________________________________________
> __________________3333333333333333333333________________________________
> ____________________________________4444444444444444444444______________
> 2222__________________________________________________222222222222222222
> FuelFuelFuelFuel________________________________________________________
>
> In this case, 1 gets most of the fuel, 2 gets a little, and 3 and 4 get
> essentially no fuel.  That's what I mean by "won't get any fuel".
>
> >   I've run some 5.7 TBIs with both a 730 (8D), and the 749 (using the
8D),
> > and while not perfect, for an as installed calibration, they weren't at
all
> > bad.  Yes, work was need but there was worked needed for the 747 too.
>
> Was the 5.7 running on all eight cylinders, or could it have been
> running on just four?  Perhaps the more complex runner configuration of
> the "dual plane 2bbl" intake manifold mixed the fuel around better.
>
> --
> Ludis Langens                               ludis (at) cruzers (dot) com
> Mac, Fiero, & engine controller goodies:  http://www.cruzers.com/~ludis/
>
>
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