Partial success - final take

[Walter Sherwin]

PFI injectors means, "Port Fuel Injectors"......

The big 'ol TBI injectors were originally designed to produce a very wide
hollow cone of fuel, that ideally was to have been sprayed overtop the sweep
of the blade beneath.  If you  remove your blade/shaft assembly, then this
is no longer a criteria that should constrain you.

Instead you will be left with a "hole" into which you want to mist evenly
distributed fuel droplets, to feed the connected cylinders.  This can be
accomplished with properly selected PFI style injectors, either mounted
vertically in place of the original TBI injectors or inclined from the
centerline to save on packaging height and plumbing complexity.  By
inclining the injectors, you will gain considerable airflow, as the
predominate direction of airflow into the "hole" will now be vertically
rather than horizontally.

There are two critical aspects when selecting PFI injectors to replace TBI
injectors in such a case.  1) find a plume/dispersion pattern(s)  that fills
your hole evenly, and  2) find an injector with an electrical coil
compatible with your ECM (ie: P&H or saturated).  I'd be tempted to first
look at some of the tight Bosch pintle designs.  A good starting point is to
get ahold of Kinsler Fuel Injection, and request their latest catalogues.
These are an interesting compendium of injectors and EFI stuff.  From that
point onward, it all comes down to trial and terror, and imagination.  If
you know of anyone with an injector flow/cleaning bench nearby, then go
spend a Saturday morning flowing different injectors that they may have on
hand just to get get a mental picture of what things "look" like.

Incidentally, if you angle the injectors externally into your "hole" (say 45
degrees), then   A) your injector bodies are out of the airstream path
resulting in fewer flow losses, and B) all of your plumbing can be external
to your pressurized air bonnet.  Adding two mirrored/opposed injectors per
bore helps to even both the mix and directional bias of the fuel
distribution within the plenums.

Actually, when perfected, what you have proposed can work very well.  Use
your compressor device to compress/deliver the air charge.  Then inject well
atomized fuel into the discharge tubes/plenums containing the warm/hot air.
Reap the benefit of both the subsequent wet manifold mixing/turbulence, and
the latent heat of evaporation of the fuel, while not having to worry about
a potentially explosive cocktail mixer perched atop your intake manifold.

Walt.






> <Yes, the small areas between the TBI throttle blade edges and the bore
> walls
> <play a HUGE role in fuel atomization in TBI setups.
>
> Bugger, thought that might be the case, but it'll be fairly easy to try
and
> at least experience what happens.  After all I'm really more interested in
> gaining experience doing this.
>
> <If wanting to attempt a bladeless quasi-TBI blow-thru fuel delivery
> <mechanism for a wet manifold & dry S/C application, then perhaps think
> about
> <installing PFI injectors in place of the TBI injectors downstream of the
> <S/C.
>
> PFI injectors ?
>
> <What you have proposed is not new, but needs a fair bit of research to
> work
> <right.  Ideally, true port fuel injection is the best way to go in
> <conjunction with the throttle upstream of the S/C.
>
> We'll its taken 2 years so far, so a another year more or less (sulk,
sulk,
> I miss the 850).  I have looked at trying to machine 4 injector holes for
> tpi, but if you go through the side there are 4 spark plugs in the way,
and
> if you angle down from the top, there's a big section of coolant area in
> each end that gets in the way (including thermostat outlet and temp
> sensor).  hence the reason for going tbi.
>
> Dan  dzorde at erggroup.com
>


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