[Diy_efi] New project

[Chris Vondrachek]

Hi Dennis,

I can answer a couple of your questions based on experience I gained
designing/building SD systems over the years.

>I am wondering if there is an advantage in going with a synchronized setup,
or
>just go asynchronous based on a small timing loop.

I'd say you could get away with it.  My first EFI system ran async to the
engine, but I learned that there is a drawback of doing this.  If you run
async, you'll have to compensate for engine rpm changes manually... that is,
if the engine runs 2x the speed, you'll have to double the fuel injection
pulses (assuming constant VE).  By implementing an EFI system that's sync'd
to the engine in some form or another, you automatically take care of the
rpm variable (plus you won't have to deal with adding multiple injector
turn-on times).

>I have no problem with the theory of speed-density sounding fine and dandy,
>but of course I don't know how it really works in practice,
>Obviously the volumetric efficiency is a question mark,

Check out my efi site... http:\\efi.cjb.net (sorry about the pop-ups).
Between the descriptions of my "UPEFI" and "VEFI-II" systems, I think you
should be able to get a good idea of how I chose to implement an SD EFI
system w/ a microcontroller (very GM-ish... but I never looked at GM code...
I swear).  It's by no means the only way, but it does work really well in
practice.  There's also some of my old code stashed in the "UPEFI"
section... I've cut out most of the implementation specific code, so you
should be able to see how the basic VE lookup was coded.

>because of the constant load and lack of cat. convertor is it necessary to
persue a
>perfectly stoch. mixture?

Other than economy... I don't see why 12:1 would be a problem.  Cylinder
washing doesn't start until around 10:1... I think.

>Even the 4 MHz part should be fast enough to calculate injector pulse times

No problem... if you keep it simple, you can run EFI on a 2MHz HC11.  I had
a HC11 system that would run an engine at 14krpm (tested w/ signal
generator).  As long as you make a reasonable attempt to code a prioritized
OS, you shouldn't have any problems.  You'll need more cycles if you start
to add "extra" stuff like data logging, serial communication, etc.  Even the
8MHz HC12 that my current system is based on gets a little stressed when
being bombarded by serial comm requests. ;^)

later,
Chris Vondrachek
efi geek & datsun nut
Hillsboro, Oregon


_______________________________________________
Diy_efi mailing list
Diy_efi at diy-efi.org
http://www.diy-efi.org/mailman/listinfo/diy_efi