Batch EFI on Siamesed Port Motors

[Bruce]

Shared port heads are just headaches, IMO.  Do what just seems best and get
on with it.  I know SEFI, sounds so cool, but the basic mechanical
configuration is so poor that you'll never really make up for it.
  Also depends if the manifold is a downer, or sider (<G>).
If your blowing the fuel onto the manifold floor, you deep in the woods
anyway.  Try for best atomization at low speed (TBI), and go from there.  If
a sider and high rpm then the port config would sound best.
Plenum volume, injector placement, on something like that is going to be
just compromises.  Figure out where you want it to run, and take you hits in
the off areas.  Trying to compromise too much leaves you with nothing that
is right.

As I recall, weren't some using just a single 26mm choked single barrel of a
45 DCOE?.
What size injectors can you even find for something that small (hmm,
975cc's?)?.
A single TBI might not be a bad option.
Bruce
  YMWV





----- Original Message -----
From: "Peter Gargano" <peter at techedge.com.au>
To: <diy_efi at diy-efi.org>
Sent: Thursday, August 16, 2001 7:18 PM
Subject: Batch EFI on Siamesed Port Motors


> I'm after thoughts on a practical problem of adding EFI to SOME
> vehicles with siamesed inlet ports of a certain configuration.
>
> A Mini has an IGN firing order of 3-4-2-1 (ie. 1-3-4-2) and inlet
> ports 1-2 and 3-4 are siamesed. If a single injector is used for
> ports 1-2 and another for 3-4, and a batch fire scheme is used,
> then, looking at the 1-2 siamesed port, that injector will fire
> during IGN events 3 and 4 and both the 1 and 2 sections of the
> siamesed ports will collect fuel equally (assuming a precisely placed
> injector) as neither cyl. 1 nor 2 inlet valves will be open. When inlet
> valve 2 opens, I'm thinking that some of the fuel that has accumulated
> for cyl 1 will be "stolen" by 2, and that cyl 1 will therefore not get
> as much accumulated fuel as 2. So, I'd expect cyl 1 and 4 will run lean
> compared with 2 and 3.
>
> I don't know how "bad" this effect is yet, but I know some have run a
> Mini with a GM two injector batch fire setup (1227165/808). Hopefully I
> can get some figures, with the DIY-WB hardware, that I can share.
>
> One partial way around this problem is to run a two bank (or a
> two cylinder SEFI) system, but I suspect that cylinders 1, 4 and 2, 4
> actually have different volumetric efficiencies (VE) so that fueling
> will still be different between cylinders. Of course, this same
> problem exists for a carby setup too.
>
> Any practical thoughts for a solution while keeping the existing
> siamesed head? I had thought of having two VE tables - anyone seen
> this in practice? I'm sure it won't account for all running conditions
> though.
>
> Peter.
> --------------------------------------------------------------------------
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