answers to some fan questions Be nice

[mark kibort <mkibort@xxxxxxxxxxxxxx>]

Message text written by INTERNET:bmw@domain.elided
Murf, your answers below,    good questions though.

1) If readings were made on a dyno, the intake air to the fan-less car is=
,
I assume,
stationary.  When a car is driven, the air might get packed a little bit,=

lessening any
advantage which the fan might give on the dyno.

>>>>>>>>>measurments to the air box were taken at speeds up to 120 mph an=
d
no relief from the vacuum was measured.  .5 psi (neg)  at  5 to 6000 rpm =
=2E
red line in 3rd and 5k at 4th.   so, with the fans on , same speed the
vacuum was relieved and .25 to .35 pressure generated.      The fan has s=
o
much extra cfm , that it will just add to whatever would be naturally dra=
wn
by the engine,at meet its own pressure capabilities
Plus, ram air is very ineffective at speeds less than 80 mph.   so, that
being said, do a little test .  hold a book out of the boundary layer or
the car, out the window.   see how much force it takes to hold it flat
against the wind.   Since books are about a square foot,  =

1 psi would be 144 lbs, even a small book would be  50 lbs.   so the
reality is that you have to have pretty efficient ram set up to do any
good.    so , ram air dosnt happen unless you are an indy car or a dragst=
er
with the scoop above the boudary layer.

2) When the fan isn't being used, does it mess up the intake airflow, and=

thus
decrease efficiency?
>>>>>>>>>>>>We did a bench test of the flow, and because it is an axial
flow fan , and most inlets have a neck down area or  a couple or turns. =

the turns create the most losses . ( unless vained)    we ran the fan on
the car off the car and with the fan ON.  =

as expected the plots on the dyno curve were no different with the fan of=
f
and still on the car vs the car stock.   Plus, if you think about it ,
under part throttle, where is the bottle neck, yes, the throttle valve is=

closing off making a big restriction and plenty of vacuum in the manifold=
=2E =

 if you  were not getting the air you need , you could open the throttle
valve more.   If you could , lets say, take the fan out of the stream and=

then you got more air flow, you would have to close the throttle even mor=
e
to keep your current hp setting.    So,  anyway , the fan creates no
measureable restriction, and I have been driving it on my car for over 6
months now, and have been getting the same gas milage.   ( maybe more
because it acting like that tornado fan product  , sold at autoparts
stores, just kidding about the tornado toy )

3) If the fan takes energy from the battery during use at WOT, and then t=
he
battery
re-charges during cruising, is this not nice?

>>>>>>>>>>>>>>it takes energy from the alternator as one of the geniuses
had pointed out, even then, it is only  30 amps, and only on for 7- 10
seconds at a time at a race track, let alone on streets.       Its like
listening to your stereo loud for 10 seconds.  No big deal.  Ive been usi=
ng
a lightweight VW battery for the last 2 years.    the battery is still go=
od
and the brushes on the alternator are as well  =



4) If #3 is true, then does this over-burden  the charge system?
     This is what my little brain has picked out as being unanswered.

>>>>>>>>>>>>>>>this was a whole discussion last week, but glad to answer
you =

                              Murf '87 328is
<

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