To stimulate discussion, I'm posting this reply to everyone:
Rick,
> Tim,
>
> I thought that most of those guys that sell those ignition systems had one
> that would work in the Spit.... Maybe not anymore...
>
> Propane - what a great idea - where did you find someone that knows how to
> to do the carbs?
>
> rkg
>
> (Richard George)
>
> P.S. I 've thought about doing that conversion several times - maybe
> someday...
>
Sorry to reply so late. I really AM interested in discussing this
stuff, just busy.
Thoughts:
If I change my V-belts to timing belts, I can put a belt-driven
timing sensor wheel pretty much anywhere on the front face of
the engine. Biggest deal would be the new crank pulley.
One could bolt something on top of the cam chain drive wheel;
nice, clean environment, albeit with oil splashing around.
What is the RPM sensing limit of an ABS wheel sensor? Here is
a ready-made speed sensing package for hostile environments.
One can count flywheel teeth, however there's clutch dust in there.
I have requested info from the people that make MSD ignition
modules. However, none of their products have a vacuum input
for load-based timing adjustment.
On propane:
I have talked to Petrolane in Atlanta. They will do the whole
thing, for not THAT many hundreds of dollars, complete with
dyno tune! The carbs are even simpler affairs than SUs. The
canonical way to control rich-lean bias is to control the pressure
of the propane inlet. This isn't so difficult because there is
essentially a 2-stage regulator in the vaporizer unit that expands it
from liquid to gas. A reference pressure source to the regulator's
second stage controls output pressure. Thus controlling air
pressure at a certain point sets the mixture. I have talked to
the gurus at Impco (carb manufacturers) who are working on a
more sophisticated injection system for V8s and use mass-flow control
to set mixture. They set it to stoichiometric for all situations!
There is no problem with fuel mixing or atomization with gaseous
fuel, so the typical cold-start enrichment is superfluous. What
does seem to be critical is ignition timing, since the absence of
liquid cooling to the valves makes them more vulnerable to burning
given a late firing (combustion still going on as exhausts open),
hence the interest in crankfire ignitions.
Regards,
Tim
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