Alternate fuel EFI

[Darrell Norquay]

Markus wrote:

> Greetings from the Great White North (Canada)

How's it goin, eh?  Ya hoser...

> 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.  

What the heck kind of a mixer is this?  Thought I'd seen em all...

> 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, 

All propane mixers suck!  I haven't found one yet that does a decent job
of it.  Tried Impco, OHG, and now I'm running a Century mixer, on my 350 
Camaro engine.  BTW, you can fix the air filter thing with a balance line.
On your vaporizer (evaporator), on the top side where the large diaphragm 
is, there's a port which is normally just an atmospheric vent for the back 
of the regulator diaphragm.  (May have a little brass screen in it) Tap this 
out to 1/8" NPT (it's the right size already), put in a large STRAIGHT hose 
barb for at least 3/8" ID hose.  Run the hose to another fitting which 
goes through the air filter housing to the inside of the filter.  This 
effectively references the vaporizer regulator to the pressure on the 
back side of the filter instead of just atmospheric.  This will eliminate
the running rich with a dirty filter.  Or, you could just change the 
filter once in a while... :]

> 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 

I'd be interested in some more details on this system, costs, who sells
it, etc.

> this system is good, I am consistently running 18 MPG city or highway.

Damn, 18 MPG is just a dream with me,  my engine gives about 12 around
the city...

> 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.

Most propane mixers (carburetors) aren't designed for decent airflow.
Add to that the fact that you usually have 2 carbs stacked one on top of 
the other, and you're lucky to flow 450 CFM...  The Century mixer I'm using
has excellent air flow, and a nifty setup for distributing the fuel into
the airstream, but the fuel metering is sh*t.  I want to do a TBI injection
setup to start out, and possibly upgrade to port injection as time and money
allow...  BTW, you can buy rebuild kits for the vaporizer for around 30 
bucks, beats hell out of buying a new one.  Piece of cake to install, too.

> 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)?

This is probably not gonna work.  Problems you would encounter with liquid 
propane are:
     
1. sudden demand for fuel causes the fuel pressure to drop so fast that the 
propane "boils" in the fuel lines, causing gaseous fuel to go through the 
injector and lean out the mixture drastically, usually with nasty (read 
expensive) consequences.

2. Injecting liquid propane into a throttle body would freeze the thing 
solid in minutes.
     
3. I haven't found any fuel injector which would open above about 80-90 PSI.  
Some Aussies did some work with a port injection system running at full 
system pressure, but they had an in tank fuel pump which circulated fuel past 
the injector a la most OEM fuel injection systems.  They had to jack up the 
voltage to the injector to something like 32 volts to get it to open.
     
4. It may be difficult to get the injector to work accurately with the 
widely varying fuel pressures you get with temperature.  At low 
temperatures, it probably couldn't supply enough pressure for the injector
to run the engine, and at high temperatures, you'd have too much pressure
and couldn't get the injector to shorten up the pulse width enough.

The current idea I'm working on is to use the fuel in the gaseous state,
using half a standard vaporizer, (remove the fuel pressure regulator guts)
and regulating it with a standard gas regulator to somewhere around 50-60 
PSI (maybe higher).  Feed this into a standard dual TBI type injector, and 
see what happens.  The higher-than-normal fuel pressure should allow the
injector to supply enough fuel (even though it's designed for liquid fuel) 
but not so high as to affect the opening time.

> The engine is a 350 stroked to 383 using Kieth Black silv-o-lite

Yeah, when my 350 bites it I'd like to go with a 383 conversion...

Anyway, speaking of long winded...  Keep in touch, man, I am serious about
doing this.  Propane should be the fuel of choice, at least here in Canada,
an' it's CHEEP!  I been running it for years, and bitching about the lack 
of performance the whole time.  It's time we dun somethin 'bout it...

regards
dn




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 Darrell A. Norquay              Internet: dn at dlogtech.cuc.ab.ca     
 Datalog Technology Inc.         Bang: calgary!debug!dlogtech!darrell
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