DFI, Batch Fire, and other myths

[Greg Hermann]

Hi--

I just couldn't resist jumping beck into this one!!

Yes, Andy, you are right. Problems for most efi are:

1. Most injectors  do not have enough dynamic range to be able to inject
all the fuel for WOT power during just 80 to 100 degrees of crank rotation
AND be able to turn down far enough (Can't go to a short enough pulse
width) to inject a small enough quantity of fuel for proper fueling at
idle.

2. Most efi injectors do not atomize the fuel very well at all, period. So
tricks such as squirting fuel against the back side of a closed, hot intake
valve are used to get the fuel vaporized. (Vaporized is distinctly
different from atomized, this is not just a semantic point.)

There are OBVIOUS benefits to timing a squirt of WELL ATOMIZED fuel with
high inhale velocity in the intake ports. Anybody who doubts this
statement, get back to me after perusing some dyno data for an engine, any
properly tuned engine, equipped with an IR intake manifold with Weber,
Delorto, or Mikuni/Solex IR carbs. Pay particular attention to how LOW the
bsfc numbers are when it is tuned properly. Try the same engine with either
a standard carb and wet manifold or TPI. When running the TPI test,
restrict the Manifold runners with a choke the same size as whatever
venturis were used in the IR carbs, so that air flow is equal. We all know
that the IR carbs will seriously outperform the wet manifold. What is not
so obvious to all is that:

 1. The IR carbs will give lower bsfc at part throttle than the TPI,
because they atomize the fuel so much better.

2. The IR carbs will geve significantly more power, together with lower
bsfc,  (remember, air flow has been equalized) at WOT both because they
atomize the fuel very well, and because they time the shot of fuel with
high inhale velocity in the port.

There would be a lot less debate about this if anybody had ever bothered to
set up a true, change only one variable at a time, test of it. (I don't
know of any such tests.)

There are several very clear performance, economy, durability, and
thermodynamic benefits to getting well atomized, but not vaporized, fuel
inside the cylinder and getting the intake valve closed before much
vaporization takes place. The finer the atomization, the better, and the
less vaporization, the better. Good IR carbs do this pretty well. Efi,
(meaning TPI) despite all of its obvious airflow and metering accuracy
benefits does not do these two things very well at all with current
injector technology.

There are lots of folks in the industry working on developing ways to make
efi do these things better. I am working on the same thing as a hobby. When
I get an engine built, and get some test results, I will share them. But
some money is definitely going where my mouth is!!! That is so because I
believe that the above outline of the situation is sound
engineering/science and I want a better performing engine(s).

Regards, Greg



>Is it true that none of the firing methods actually time the injector
>to the intake stroke of that cylinder?  I would think that injecting
>fuel on the other strokes would be a waste.
>
>Andy
>
>
>---Sandy <sganz at wgn.net> wrote:
>>
>> I think that injection of all the fuel during a period has some
>SMOG/Econ
>> bennifits, but can't remember if any power was gained (anyone?).
>Others
>> have stated that the evaporation of the fuel sitting on the closed
>valve is
>> better then squirting raw liquid fuel (hard to burn) into a
>cylinder.  I
>> think that is why you don't see much power difference between SFI
>and BATCH
>> systems.
>>
>> Sandy
>>
>> At 10:17 PM 1/20/99 -0600, you wrote:
>> >
>> >
>> >Ward Spoonemore wrote:
>> >
>> >> Tom
>> >> Your Edelbrock ProFlo is typical on several other EFI system's
>> >> actualy the tests I have run show little on no differace between
>L/R and
>> >> other systems.
>> >> In fact all EFI are on almost 100% at or near WOT.
>> >> Ward
>> >
>> >There is an ongoing discussion about the need to inject all (or
>most) of the
>> >fuel while the intake valve is open, probably starting before the
>valve
>> >opens and ending before it is closed. It would require large P&H
>injectors
>> >and lotta of pressure.
>> >
>> >Any ideas or comments (or experiences).     Regards  Tom
>> >
>> >
>>
>>
>
>_________________________________________________________
>DO YOU YAHOO!?
>Get your free @yahoo.com address at http://mail.yahoo.com