DFI, Batch Fire, and other myths

Bruce Plecan nacelp at bright.net
Thu Jan 21 18:01:17 GMT 1999


-----Original Message-----
From: andy quaas <realsquash at yahoo.com>
To: diy_efi at efi332.eng.ohio-state.edu <diy_efi at efi332.eng.ohio-state.edu>
Date: Thursday, January 21, 1999 12:28 PM
Subject: Re: DFI, Batch Fire, and other myths

Check out Barry Gant's EFI system.  It uses venturi
Bruce


>Doesn't a venturi atomize fuel very well in any case?  As stupid as it
>sounds, why not make an intake that has a venturi for each port and
>feed the fuel to the venturi at each intake port.  You'd have a lota
>throttle shafts and such, but it would atomize the fuel better, no? 
>What mechanical devices atomize fuel well?  How well does a mechanical
>injection atomize fuel?  
>
>Andy
>
>p.s. what does IR stand for?  
>
>
>---Greg Hermann <bearbvd at sni.net> wrote:
>>
>> 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
>> >> >
>> >> >
>> >>
>> >>
>> >
>> >_________________________________________________________
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>> 
>> 
>> 
>
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