Programmable ECU's (Was GM TPI tips for a newbie)

[Frederic Breitwieser]

 > Which system(s) is/are considered the best?

Well Charles, they are all good, and they all suck.  <grin>

The Holley Projection system is more of an analog system,
like a carbeurator, with enough sophistication to make for a
reliable, stable air/fuel system.  Advantages are that its
replaces your carb, so your regular everyday existing intake
manifold would be just dandy, thus reducing the overall cost
of converting to EFI.  Another advantage, is you can change
the settings very easily, using either a "black box" or a
laptop, depending on which model you buy, and update your
settings if you decide to toss say, your stock cam, and
through in a "thumper" cam.  Its flexible, adaptable, and
works out of the box.  There are two major drawbacks that I
see - first, it uses your intake manifold, which means your
rough idle due to fuel "sheeting" on the walls of your
intake manifold still exist, and it doesn't utilize an O2
sensor (that I know of), therefore its not a feedback
system.  If you are concerned about emissions, this
obviously can become a problem.  Throttle Body EFI, where
you have few injectors (one to many) servicing many
cylinders, all experience this sheeting problem in a worse
case scenario.  Sheeting is when the fuel collects along the
intake runners, then as the miniscus of the fuel is
exceeded, it slothes off into your cylinders.  Another
example of a miniscus is when you overfill a glass of water,
and have the water higher than the glass, in a sort of
bubble - this is the miniscus - or the natural attraction of
molecules that is stronger than the force of gravity against
its own weight.  Sorry for the horrible explaination, its
been ages since I've opened a science book.  The other draw
back of a wet-style manifold is that certain cylinders
typically get more fuel than others, since the carb unit or
throttle body is located in the center - takes fuel longer
to travel longer distances.

Now, this means my opinion is that multi-port EFI offers a
lot of advantages.  First, is the sheeting problem
disappears entirely.  Because air is much more movable than
fuel, your manifold design is not as mission critical as in
a wet design, therefore you can get away with a lot more so
to speak in manifold use/design/construction.  Also, most,
if not all, multi-port injection systems (like Electromotive
& Haltech, two name two of many) can control each injector
independantly, based on feedback from an o2 sensor.  This
means that your computer, based on RPM, load, temperature,
manifold pressure of vaccuum, can determine the "right"
amount of fuel necessary to match the airflow, which you as
a driver determine with your gas pedal.  This higher level
of control obviously is more desirable, especially in a high
performance/low emissions application, but it really costs
more.  You have more sensors, fabrication if you are not
using and OEM EFI system on a similarly styled
same-manufacturer engine (as in, late model camaro EFI on a
1969 Caprice, for example).

I've never had the opportunity to play with the DFI system,
however I have played with both the mid 80's OEM GM systems,
as well as the Haltech ECMs and the Electromotive ECMs.  For
flexibility and control, I prefer the Haltech.  I managed
with a little electronic add-ons to drive three injectors
per cylinder mixing different fuels into a twin-turbo V6. 
With the Electromotive unit, I struggled and struggled to
get it right, which I never did.  Don't get me wrong, the
Electromotive is a good, reliable unit, and their tech
support is really good.  I asked them a lot of stupid
questions and they were patient and gave me a lot of good
answers.  When they didn't know, which was rare, they stated
such.  I also found that the electromotive units were easier
to start off - the "Maps" for generic engines were
reasonable and close to what I needed, therefore instead of
spending a day entering data, which are guesses at best, I
could use an existing map or profile, and "tweek" from
there.  In contrast, the Haltech unit was significantly more
flexible, but at the cost of being able to attach, turn on,
and at least start the motor and tweak from there.  The
included maps didn't fit my application at all.  THough, I'm
sure Haltech doesn't have lots of call for twin turbo 3 inj
per cyl V6 applications, to be entirely fair.

One of my many slow moving projects is to convert a Chrysler
383 stroker (431 cid) to run under the OEM GM system I have
leached from a junkyard, including all sensors, MAP, O2,
water temp, crank, etc.  The intake on the 383 has already
been milled to support an injector per cylinder, however I
have not welded in the bosses yet.  I still have the engine
apart trying to figure out the insides.  Anyway, long story
short, the only issue I see is fabricating the crank sensor
mounting bracket, and making it adjustable incase my bracket
is off.

There is a book by Jeff Hartmann, called "Fuel INjection
something", I don't recall the exact title, but it does
cover installation and tuning of the Holley system, the
Haltech system as well as the Electromotive system, and
basic theory, math formulas, in case you want to fabricate
your own system either from scratch, or from oem parts and
ECMs.

While this is not the answer you want to hear, I can't say
for sure that any one system is better than the other.  They
all have advantages and disadvantages over each other, and
different price ranges to boot.  I'd highly recommend Jeff
Hartman's book - for 20 bucks it gives you a good overview,
and some actual installations on specific units, and from
there, you can make a better choice.  Sorry I don't have the
exact title, but it has a black cover and you can't miss it
:)


-- 
Frederic Breitwieser
Bridgeport, CT 06606

http://www.xephic.dynip.com
1993 Superchaged Lincoln Continental
1989 500cid Turbocharged HWMMV
1975 Dodge D200 Club Cab
2000 Buick GTP (twin turbo V6)