direct injection propane

[Jim Steck]

>My questions are: Is my 
>understanding of the way a TBI regulates fuel accurate?  How well would 
>the nozzle withstand the higher pressures of propane(up to 120 PSI)?
>when the vehicle sits and under the hood heat causes vapor in the fuel
>line how well would vapor blow through the nozzle at startup?  How low
>can the fuel pressure go before the nozzle won't work(at -40 you can
>carry propane in a bucket)? finally, how many nozzles would I need to
>feed enough fuel?

1) 'EFI' controls fuel delivery by adjusting pulse width of the injectors, but
the pressure to the injectors has to be controlled.  There are several pressures
used, but for TBI it's about 1 bar above manifold pressure.  The pressure
regulator has a reference port to the manifold and maintains the pressure
differential between fuel and manifold . . . reason . . . the injectors have a
minimum 'open' time.  If you had a high pressure differential across the
injector at high manifold vacuum (like at idle), fuel delivery would be too much
even at minimum 'open' time.  If you pick a smaller injector to reduce flow at
idle, you won't have enough flow at WOT.

2) I would not expect the injectors to be reliable above 6 or 7 bar (they might
not open).

3) The vapor will cause hard starting, but it will surely pass through the
injectors.

4)  Most TBI systems I've seen (gasoline) use two injectors.  Your flow rate
seems to be similar.  The injectors are available in different sizes.  I don't
know what the lubricating properties of propane are . . . perhaps none . . . or
if the injectors will survive propane long term.

Try calling Ak Miller in California (310) 949-2548 . . . call early (5 - 7 am
Pacific time) and talk to AK.  They use propane in many of their turbocharged
systems (some very high horsepower).  I don't know how they control (inject) it.

-Jim Steck

Are you using any kind of instrument to monitor the fuel mixture?  For a modest
price ($130 - $180 US) there are several (some better than others) meters that
read the O2 sensor and give you an immediate display of mixture.