Batch EFI on Siamesed Port Motors

[Peter Gargano]

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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