Mike, If you really want something to think about concerning EFI systems,
check out www.fastmanefi.com. Rich Nedbal is a well respected EFI expert,
author, Mopar guy, and regular poster on Moparts.com. At this link,
www.fastmanefi.com/TechDownLoads.htm you can download several tech articles
he's written. Pay particular attention to "All you wanted to know about
EFI but were afraid to ask chapter 2". In case you can't open Word
documents, I've enclosed some excerpts concerning the various types of EFI.
-------------
"Speed Density Systems:
A Speed Density system merely looks at how far the throttle is open, the
intake manifold vacuum, and RPM. An SD system can obviously deduce the
engine load, just as you could, by looking at these parameters. For
example, if the throttle is open, say past 50%, and the intake manifold
vacuum is low, and the RPM is only 2500 RPM, wouldn’t you say this engine is
being loaded? And if the throttle was closed, and the resultant manifold
vacuum was high, yet the RPM is 3500 and slowly coming down, wouldn’t you
say that you just backed off on the throttle from a high speed cruise and
are coasting down?" (I'm leaving out the Volumetric Efficiency graphs he
shows)
"Alpha-N Systems:
In cases where an engine’s camshaft is so radical that very little vacuum is
produced, the change in vacuum may not change enough to reliably compute
fuel requirements. In these cases the VE table above is replaced with actual
injector pulse widths. This approach is much harder to work with, but for a
race engine where all you really need is to start, idle (sort of) and full
throttle, Alpha-N can work.
Mass Air Systems:
In theory, if the ECU knew the mass of the incoming air it could do a better
job of computing the engines fuel requirements. “Mass Air”, as it is
called, would automatically take into consideration humidity, altitude, etc.
In addition, less human tuning would be required because as long as the ECU
program knew the characteristics on the engine, together with the mass of
the air, the system could self adjust.
Most of today’s OEM EFI systems use mass air for this reason. Why aren’t
all the aftermarket systems Mass Air? Mass air sensors use hot wires in the
throttle body. These wires have to be short to not be fragile. This limits
the diameter of the throttle body. Dual throttle bodies add a level of
electronic complexity and equalization that no one wants. If you want a lot
of horsepower with a mass air system you have to work at it, and you still
have to start with a system that is optimized close to what your engine
needs.
Summary:
Most aftermarket EFI systems use Speed Density because it’s easy to program,
fairly cheap, and works very well with any size engine. Alpha-N is only for
racing. Mass Air is very good for smaller engines that don’t need larger
throttle bodies."
-----------
Hope you found this interesting, Mike. In a nut shell, there's nothing
wrong with the Speed Density systems Mopar uses. You would be surprised
how far you can go with engine mods on a emissions legal MP PCM if you
choose your parts carefully. Just look at the mods I've made to my Dak at
the link below....and mine is considered mild compared to several of the Dak
racers I know who are way quicker than I.
Ray
http://www.dragtruk.com/ENTRIES/20KM1FD2KWBP.html
> -----Original Message-----
> From: MICHAEL CABE
>
> just something to think about,speed density systems vs mass air flow.
>
> --- On Fri, 9/17/10, Ray Block <BPracing@wowway.com> wrote:
>
> > From: Ray Block <BPracing@wowway.com>
> > Subject: RE: DML: Re: K&N fipk
> > To: dakota-truck@dakota-truck.net
> > Date: Friday, September 17, 2010, 6:26 PM
> >
> > > -----Original Message-----
> > > From: MICHAEL CABE
> > : Re: DML: Re: K&N fipk
> > >
> > >
> > > jon,
> > > i found this very interesting.
> > >
> http://www.carcraft.com/techarticles/electronic_fuel_injection/index.html
> > >
> >
> > Mike, while I'm not Jon, I am curious as to what you found
> > so interesting in
> > that Car Craft article. ??
> >
> > Ray
> >
> >
> >
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