DIY_EFI Digest V4 #572

[Rich M]

Date: Sun, 10 Oct 1999 14:23:19 +0100
From: Ade + Lamb Chop <alaw at mrc.soton.ac.uk>
Subject: Re: DIY_EFI Digest V4 #570

At 15:00 09/10/99 -0400, DIY_EFI Digest wrote:

>>Don't lose sight of the big problem with mini's - siamesed ports! For
those
>>not so familiar, the head has two inlet ports which each split in two to
>>feed two inlet valves; Cyls 1&2 are fed by one inlet tract and cyls 3&4
fed
>>from the second. Throw the firing order into the equation, and you will
>>appreciate the problem of mixture distribution, specially from a throttle
>>body injection arrangement. for this reason, Mini's run with uneven
mixture
>>across the cylinders even with carbs that feed fuel into the airstream
>>continuously. Consider what happens when you inject pulses of fuel into
the
>>airflow way back at the throttle body, synchronous with the engine cycle.
>>This is why I believe some (if not all) TBi sytems inject 'asynchronously'
>>(randomly?). Certainly Vauxhall/Opel Multec TBI systems inject 5 pulses
per
>>cycle to try and spread out the uneven distribution so that each cylinder
>>gets a fighting chance of seeing reasonable mixture on average.

>Carbs manage it acceptably I was thinking of just streaming fuel in the
>same way carbs do. After all Tbi is just a carb with an injector controled
>by a processor rather than 'machincal means'

Ade,
The point I was trying to make (and it's pretty significant), is that you
can't 'continuosly stream' from a TBI injector, it's either on or off, it
squirts defined amounts of fuel at predefined intervals. Theoretically, you
could turn on and off a lot more times in the engine cycle to approach the
carb 'model', but I think if you use a big enough injector to cope with high
load flow, you'd run into calibration problems at low speed because of the
short 'on' period.
I've been trying to confirm if Rover use the same principle as GM, ie.
asynchronous injection - no answer yet....

ps. take your point about Arden/KAD heads; just covering myself in case I
was up the wrong tree.
Rich.