DFI, Batch Fire, and other myths

[EFISYSTEMS at aol.com]

Hi Greg,
       I couldn't agree more...if you can program a computer to learn when the
intake valve closes and know the bsfc and know the mass fuel and mass air and
know the actual torque produced from an event(given igntion timing has been
introduced to optimize) there has to be a calcualtion that can result in a
generic rule.......fuel injection has so many variables that carb's have for
granted....the pulses that hit the boosters in a carb are relatively "easy" to
tune considering a "programmer" has no idea of the sonic wave of a engine
cycle vs rpm and exhaust and camshaft intake or exhaust events vs temp or
density...we have just begun to start learning what happens.....and we haven't
even started to talk about transport delays depending on temp or
distance......steady state is the easiest,,,,but then there are the
transients......how do you do it for every app?????  That's what I want to
know!!!!!.....Anyway I'll shutup now.........Thanks for listening
-Carl Summers

In a message dated 1/21/99 7:53:16 AM Pacific Standard Time, bearbvd at sni.net
writes:

<< Subj:	 Re: DFI, Batch Fire, and other myths
 Date:	1/21/99 7:53:16 AM Pacific Standard Time
 From:	bearbvd at sni.net (Greg Hermann)
 Sender:	owner-diy_efi at efi332.eng.ohio-state.edu
 Reply-to:	diy_efi at efi332.eng.ohio-state.edu
 To:	diy_efi at efi332.eng.ohio-state.edu
 
 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