Ram-air vs. cowl induction again. :-)

From: Jon Steiger (stei0302@cs.fredonia.edu)
Date: Fri Mar 20 1998 - 18:21:35 EST


  BTW: Brad mentioned that there is some ram-air and cowl induction info
in a book he saw: "How to build horsepower, part 2". I ordered a copy of
that (and part 1) from amazon.com, but I haven't received it yet.

  I tried an experiment I've been wanting to do for a little while today...

  When they want to study the airflow and stall characteristics of a
wing, aircraft engineers will sometimes take thousands of tiny pieces of
yarn and tape them to the top of a wing. That lets them visibly see the
path the air takes over the wing. I did basically the same thing with my
hood today. I used about 30 or so pieces of yarn placed at various
parts of the hood (mostly near the middle of the hood and near the cowl
area, where a ram-air and cowl induction scoops would be.

   Here are the results: In the ram-air area, the air flow was pretty
clean. The ends of the yarn whipped around a little bit, but there
wasn't any indication of any eddys or vortices. This leads me to
believe that a ram-air scoop would indeed be effective. Wether or not
it is more effective than cowl induction I still don't know.

  In the cowl area, I had a few strings just before the cowl grille
(that the window washer fluid shoots through), I had a couple on the
grille, and a couple on the windshield behind the grille. The results here
were kind of interesting. The strings in front of the cowl showed the
air flowing from front to back, but it seemed to split a little (left
and right) to go around the windshield. The strings behind the cowl
on the windshield showed the air flowing up the windshield. However,

the strings ON the cowl, got sucked down into it, so there is indeed an
area of low pressure there. I have no way of comparing the volume or
speed of the air there as opposed to in the middle of the hood though.
  Something interesting that happened was that a string which was behind
the right windshield wiper pole showed the air flowing from front to
back, except for when I turned on the wipers. Then, it actually got
sucked down into the hole where the wiper pole is. So, some interesting
things were happening in the cowl area. (And brings up the thought that
maybe the windshield wipers might interfere with the effectiveness of
cowl induction.)

   Here's my theory: We all know how a semi or a van will suck air
after it as it goes down the road. (Any car actually, but it is more
pronounced when the area is large.) NASCAR uses this principle for
drafting. Once I followed a tractor towing a large sprayer on my
bicycle, and the pedalling effort was considerably reduced. I think
that there is a little bit of a low pressure area in the cowl area all
of the time, but I think that a cowl induction hood, rather than taking
advantage of an already existing situation (like the ram-air simply
scoops the air up that is already flowing at that location), actually
*creates* a low pressure area. (or amplifies the low pressure already
in that area) It is sort of like having that semi sitting on your hood;
air flows along it and all of a sudden there is nothing; this creates a
low pressure area, and air can now be sucked into it. Also, the
engine compartment would be at a lower pressure than the outside air,
thus sucking air into it. (This would happen for both ram-air and
cowl induction.)

   However... Despite everything I have said, I think that the speeds
we travel at are too slow for there to be any major difference between
the two induction types. It will be interesting to see what that
book has to say.

   Because of this, I will probably go with a ram-air. If there's no
performance difference between the two, I might as well stick with the
Mopar look.

   Incidentally, I didn't really want to go with ram-air with a sealed
airbox because that is why I got my open element air cleaner in the
first place; so the engine could breathe! I don't want to close it up
again. Also, I spent about $70 on the thing, and I'd hate to waste it.
I was hoping to use the ram-air or cowl induction hood to simply
flow cold air in the general vicinity of the air intake and also
into the engine bay in general. While talking to Terry at Pro Glass
(who seems like a really nice guy, BTW), he said a guy he knows has a
Ram with the ram-air hood, but no airbox; he just lets the cold air
flow into the open element. It gave him a tenth in the 1/4 mile, so
that's encouraging.

                                              -Jon-

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   I do not speak for the SUNY College at Fredonia; any opinions are my own.



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