[Diy_efi] injector advance

[Gary]

----- Original Message ----- 
From: "Greg Hermann" <bearbvd at mindspring.com>
To: "A list for Do-It-Yourself EFI" <diy_efi at diy-efi.org>
Sent: Friday, August 06, 2004 2:11 PM
Subject: Re: [Diy_efi] injector advance


> At 1:39 PM 8/6/04, Gary wrote:
> >An informative, technical and lengthy discussion was conducted
> >in a thread 'sequential injection timing' the last week of July in
> >2002, if you have access to the archives.  Many of the more
> >knowledgeable members, posting in that time frame, posted in
> >that thread.  Recommended reading/studying if obtainable.  Hope
> >this turns out to be more than a teaser for you.
> >
> >GAS
> >
> The gist of that thread was that if you have some means of getting
> GOOD atomization of the fuel, it will give better bsfc and power if you
> can inject during the time of high air flow velocity in the intake port.
>
In addition to injector timing, yes there was noteworthy discussion on
good atomization.  In the real world however, that 'luxury' is usually
unattainable, considering the need to put injectors in a batch fire mode,
to satisfy the fuel requirement.
>
> Injecting against the back of the intake valve is a CRUTCH, used to
> compensate for the fact that most electromagnetic injectors do NOT
> give good atomization.
>
> Use an exhaust grade material (read more expensive) intake valve, and
don't
> worry about cooling it.
>
The intake doesn't get that hot in the first place, to require exotic
exhaust
valve material, so need for additional cooling is a mute point, even for
F.I.
(forced induction) applications.
>
> Evaporating the fuel in the intake port reduces power (fuel vapor
displaces
> air) and cooling the intake valve reduces efficiency.
>
:shrug:  Maybe so, in engineering discussions, but enuf to be concerned
with in the real world?  Is it measureable in the practical sense?  Again
mute, not able to get around that in an actual application, with the fuel
spraying at closed valve, a necessity under high load, high rpm conditions.
I prefer concentrating one issues I have more control over.
>
> Evaporating (well atomized) fuel inside the cylinder once the valves are
> closed provides internal cooling during the compression stroke, reduces
> negative power for the same, and thus reduces bearing loading !!
>
> You pretty much need to look at something like air assisted atomization
> for the injectors to make it work right.
>
Other than using exhaust flow to assist, I don't have any notes to support
that discussion, in original thread.  But is this practical, or even
relevant
to the original ? in this and referenced archived thread?  If not, I
personally
consider it engineering dribble.  While info of this nature makes for
interesting reading (ie educational in some way), if I am unable to apply it
with some practicality, it is not a matter of concern here, considering
original subject matter.
>
> The fact that properly TUNED IR carbys (Webers, et al) will yield lower
> full power bsfc than conventional port injectors at WOT pretty  much
> proves the point.
>
Proves little.  Yes, the webers atomize fuel very well.  However, I consider
that misleading in discussion that compares to fuel injectors.  The improved
BSFC also benefits from the 'TUNED' intake tract as well.  I consider it
misleading to reward the resulting gain completely to the atomization.  If
for point of discussion, isolation of the gain from atomization alone is not
possible, it becomes much less meaningful.  There are race engines with
BSFC in the mid 3s, and they don't use fuel injection, or webers, FTM.
While their carbs are state of the art, alot of attention went into design
and flogging of the intake manifold.
>
> Greg

>>From a practical POV, that is the way I see it.  I referenced the archived
thread, because the original post (in that thread) inquired about injector
timing, with pertinent on topic discussion resulting.  I considered that to
be helpful to thread originator here.  You know, something relevant.


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