[Diy_efi] "Wet" Manifold Questions

[Stephen Andersen]

I sent this to someone off-list, and thought it might be 
worthwhile to get list opinions/input.  If anyone thinks it 
is not an appropriate list topic, please reply off list.

As you may remember, I am working on fitting a Lysholm twin-screw
compressor onto my BMW engine in hopes of developing a kit.  I have 
made quite a bit of progress, and am hopefully only a few weeks away
from getting some of the major components (intake manifold, inlet/outlet
housings, brackets, etc) fabricated.  Lucky for me, I have a company
next door to me that develops resins for stereolithography, and the
guy that runs the shop next door has been making me some of my components
in plastic for free for excitement.  Normally he gets to make paper clips
and stuff like that for trade shows!!!

Anyway, in talking with Whipple superchargers a few days ago, they indicated
that in nearly all of their aftermarket supercharger kits, they run the 
blower wet.  In their case, they try to input 100% of the additional 
fuel requirements due to boost, into the back of the blower.  They indicated
that in their experience, it results in higher efficiency and they generally
get a minimum of .5psi more boost throughout the range, in kits that 
usually peak at 6-7 psi.  

I plan to use air-air intercooling with my setup, which will obviously
require a bunch of piping, and a big FMIC in the path between the compressor
and the intake manifold.  I specifically asked them about the results of 
adding fuel at the back of the compressor, having it go thru the compressor 
and get heated, and then taking it through a bunch of piping and an IC
that will cool it.  My concern is obviously that of fuel either dropping
out of suspension, or even condensing in the piping or IC (assuming that any
of it may have vaporized in the blower due to the added heat).  I have not 
done any calculations or anything on this yet, and I'm not sure I 
even want to!!!

There are some significant benefits to me for running aux injectors instead
of adding pulse width to the stockers, or enlarging the stock injectors
and subtracting pulse width at low rpm.  The biggest benefit is that I am
 using a piggyback MAF signal modifier for fuel and timing control.  On
my car, with a relatively advanced ECU, modification of the MAF signal
will alter the load calculation in the ECU, and in the case of adding larger
injectors, actually DELAY the onset of open loop operation.  I don't know if

this will be significant, however I will be unable to run any AFR other than
14.7:1 until I hit open loop, as I will then end up altering the long term
fuel trim in the ECU which will really screw things up.  This will mean that
during closed loop, even if under boost, I will be constrained to 14.7:1 and

have to pull timing (possibly severely) to keep detonation at bay.

With aux injectors, I can set up my piggyback to base its load calcs
on MAP (instead of TPS), and then have the piggyback use the aux injectors
any time I have indicated the addition of fuel is required.  This will
actually
allow my car to enter open loop operation EARLIER due to the presence of the
increase airflow from the compressor.  Whether I add aux injectors before
the blower,
or stick them in the intake plenum is pretty much irrelevant to this
benefit,
but my concerns over uniform fuel distribution, and more importantly
fuel puddling/condesation, etc are still valid.

Do you have any insight, direction, or experience you can provide?  Any 
recommendations for sources to see if this is a problem?  Whipple indicated
that thay do this even in their air-air intercooled kits with great
success.  Should I throw my theoretical (and unfounded with fact, at least 
at the moment) concerns aside and try what they indicate works?

BTW, in more recent considerations, I may end up trying this out, but using
an air-liquid intercooler instead to ensure a short flow path into the 
engine, and less volume of combustible mix in a long intake path...

Thanks, and sorry for the length!!!

Best Regards,
Steve Andersen
 


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