[Diy_efi] And for the bottom end of the market....

[Adam Wade]

--- peterw <peterw at waybeat.com.au> wrote:

> Why would this be so ? For a small single cylinder
> engine couldn't you just have a constant fuel
> pressure ?

Well, essentially, you can do whatever you like, just
some things are easier to do than others.

Traditionally, fuel pressure is held at a set amount
above manifold pressure, so that a certain injetor
open time will always deliver the same quantity of
fuel.

I would tend to think that having a constant fuel
pressure would be especially bad on a single, since
then you would need to have manifold pressure to
determine how much fuel was being delivered with a
given pulse width.  This would be especially necessary
with an alpha n system.  So then we're back to the
sampling problem I spoke of before.

> So, couldn't you just monitor venturi pressure and
> inject fuel accordingly(lookup table).

If you have a CV slide, and you know how much fuel is
being injected with a given pulse width, you could do
that, but again, that fluctuates greatly, so when do
you take your sample?

> I realise that air density, amongst other things
> has, an effect

Air density is partially compensated for by the vent
hole in the float bowl.

Having learned as much as I have about fueling, I'm
often amazed people were able to get carbs to work at
all, much less got them to work well.

> but if you wanted a simple "electronic carburator"

Fuel injection will never be an "electronic
carburetor", because it can't possibly operate in the
same way a carb does on a number of fronts.  One could
ask as well, "If you're just duplicating a carburetor,
why not simply install a carburetor and be done with
it?"

> My experience(i.e riding 'em) with EFI bikes is that
> most of 'em don't do EFI very well

How many have you ridden?  There are currently
something on the order of 35 or 40 models that are
fuel-injected, and that's just for the 2003 model
year.  Motorcycles have had fuel injection since 1980.

> hence the plethora of aftermarket ECU's to allow
> remapping.

There are only two aftermarket ECUs on the market that
I know of; one is from MoTeC and costs $2500 to get
into the game, and is made specifically for racing
(although there's no reason you can't use it for other
applications).  The other is specifically for
Delphi-equipped Harley-Davidsons that have had major
engine modifications.

Your analogy to cars is a poor one; the number of
sensors has very little to do with a vehicle's ability
to be "remapped", or the objectives of the original
"mappers" in how and why they created their maps as
they did.

I have a feeling you'll enjoy reading my book on the
subject of motorcycle EFI one it is published (should
be around Christmas).

=====
| Adam Wade                       1990 Kwak Zephyr 550 (Daphne) |
|   http://y42.photos.yahoo.com/bc/espresso_doppio/lst?.dir=/   |
| "It was like an emergency ward after a great catastrophe; it  |
|   didn't matter what race or class the victims belonged to.   |
|  They were all given the same miracle drug, which was coffee. |
|   The catastrophe in this case, of course, was that the sun   |
|     had come up again."                    -Kurt Vonnegut     |

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