Dual TBI units - How To Handle Twin IAC's?

[Walter Sherwin]

Thanks Dave, I appreciate the input!

My original thought was in fact to leave both TBI IAC's in place, close one,
and drive the other via the PCM.   Or, I could have also decided to drive a
single "remote" IAC, and plumb it to both compressors, and
defeat/ignore/block-off the twin stock TBI IAC passages.  Modifying or
replumbing the TBI IAC passages looks to be a big PITA, if it can even be
done without making things look "kludgy",  because the passages are integral
to the casting of the TBI and are hard to access.  I want the finished
system to look infinitely "stock".

The point that you raised is quite correct.  I do not require the flow of
two IAC's at idle, for the proper operation and/or control of the engine.
However, it would be kinda cool if I could employ  both IAC's (since they
will be there anyway) to achieve equal mixtures and pressure drops accross
both compressors.   I guess it's just another part of the desire to do
something different with this project.   In all of my previous "single" 1.5
and 2.1 compressor setups,  I've always had just one throttle and just one
IAC to play with and have never felt at any time limited due to having just
one IAC.  This will be the first time that I've had two of everything to
play with :)

I know of at least two 90454SS's that are currently running twin naturally
aspirated TBI setups, with mixed results (twin SBC TBI's & old BBC Offy
manifold).  One has had a very good experience, and one has had a very bad
experience.  I think the difference originates from the competency of the
tuner.  As far as I can tell from talking to people and researching things,
it is not that hard to make this setup work, and does not require much more
than an external P&H current box and a bit of patience.  For the guys
running the above setup, mixture distribution is a very real concern
(fortunately I will be discharging into a common plenum in my application).
I  have not yet bumped into anyone who has tried this with twin BBC TBI's,
either in  supercharged or naturally aspirated form.  Would love to talk to
anyone who has done this.   The wet flow bench seems to idicate that it
should be "doable"........


Walt.






>Regarding #4, Why not allow only ONE IAC to control the air?  I mean I hate
>to bring the obvious - but how much more air is needed at itle if saay you
>slapped 45 more TBI's on there? the idle air streams would come from
>distributed locations - at what cost?
>
>and if you did need a bit more range - the cone will stuff into a slightly
>enlarged hole, if need be, is what I'd think..
>
>I hate to sound like I know what I'm doing - I've never done anything like
>you are proposing , geeze, thats wild!
>
>
>> 1) Can I physically drive two IAC's from the single PCM IAC driver?
>> 2) If so, should I wire the two IAC's in parallel?
>> 3) For a first blush at the cal, can I simply cut the commanded IAC steps
>in
>> half?  Just looking for a starting point.
>> 4) Any other thoughts or recommendations?
>>
>>
>> Thanks a bunch;
>> Walt.
>>
>>