Alternate fuel EFI

Tue Mar 19 08:46:28 GMT 1996

Greetings from the Great White North (Canada)

My interest in EFI first came when I assisted my father in law in
transplanting a 5.0 multiport drivetrain into a '68 meteor then my
father in transplanting a 2.5l TBI into his '85 Dodge Rampage.  Both
cars were imense successes and I believe Dodge could have made money 
from this car if they were to have done this themselves!

My personal EFI story started 10 years ago when I converted my '68 GMC
to run on propane.  The original system consisted of an evaporator and
a mixer, the evaporator is basically a large welding regulator set to 
supply a presure just below atmospheric and the mixer is two plates
with a gap between them of about 1", the top plate has a smaller hole
than the bottom plate.  The mixer sits on top of the existing carb and 
gives the evaporator a vacuum signal.  This system sucked!  As soon as
the air filter got dirty the system went rich, if barometric pressure
was much different than the day the system was set, it went nuts, extreme
temperatures seemed to throw it off.  We have some extreme temperature
swings of as much as 30Deg. celcius in a 24 hour period.  Mileage 
ranged from 15 MPG to about 4 GPM (yes gallons per mile).

I eventually came across (I'll call it an Electronic fuel control
system) from a company called Technocarb.  This system uses an O2
sensor, TPS and input from the tach lead (its intended to be used on
and already EFI engine) it then uses a stepper motor to run a valve 
placed in between the evaporator and the mixer.  This controls the 
amount of vacuum the evaporator see's.  The ECM is a unit 
built by an Italian company, I think its called AFB, and appears to
run off a fuel map until the O2 sensor is up to temp.  The acuracy of 
this system is good, I am consistently running 18 MPG city or highway.
The problem with this system is that the air flow through the mixer is
poor, resulting in low power.  Also my evaporator is starting to stick,
this will be my 3rd one at $400 each.

The ECM has a diagnostics port which gives a reading from 0 to 256, 
indicating the position of the fuel control valve.  What I was thinking 
of was replacing the evaporator, mixer and fuel control valve with a TBI
nozzle controlled by a circuit which 'translates' the fuel control
valve position into an on/off pulse width.  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?

The engine is a 350 stroked to 383 using Kieth Black silv-o-lite
pistons (on the topic of alluminum metallurgy wizardry). The cam is
short duration with high lift combined with the longer stroke take 
better advantage of the slow burn characteristics of propane.  Because
propane is stable under pressure the heads are small chamber and have 
been shaved should give compression ratio of around 11:1

Sorry for the long-windedness but this is the result of 10 years of
struggling to achieve a usable aternative fuel engine.

                                Markus

P.S.    If you are wondering why anyone would do this it is
because our government taxes the hell out of gasoline but leaves
propane alone because it is envirnmentally sound.
Go green, Save that planet!