Effectiveness of RAM induction?

[Diehl, Jeffrey]

I'm very interested in this article.

We have thought about this potential problem for some time.  We might have
to use string streamers to see if there IS any airflow where our duct will
be.  Also, we have thought about putting a pressure guage INSIDE the duct to
see if it's getting any air.  When we build this thing, we will know that
it's working.

Now, what if it doesn't get any air for the reasons you cite?  Well, we have
considered the possibility of putting a small "wing" on the leading edge of
the passenger compartment to push the air stream down into line with the
duct.  Hope we don't have to do this, but it is an option for us.

Unfortunately, I don't see any other locations for such a scoop.  The
passenger-side fender is too far and across the engine.  The driver's side
is where the fuel fill is and would be too difficult to modify.  Under the
car was a (brief) thought.  Too much debris to suck up, and hopefully not
much air there, either! <grin>

Thanx for your thoughts on the subject.
Mike Diehl.
-----Original Message-----
From: Craig Dotson
To: diy_efi at diy-efi.org
Sent: 10/15/2001 8:51 AM
Subject: Re: Effectiveness of RAM induction?

> Now here is what I'm planning to do...
> From the TB, I'll go through a hot-wire MAP.  I'll have to build a
circuit
> to make the MAP look like the AFM for the ECU.  From the outside side
of
the
> MAP, it's going to trumpet out to about 8"x6" and bend up toward the
top
of
> the engine compartment.  This 8x6 intake box will come up through the
engine
> hood, where the air filter will mount.  Then I'm going to have a duct,
which
> is hinged over the rear window.  This duct will continue from the air
> filter, up and over the rear window.  I'm toying with the idea of
having
the
> duct trumpet out yet some more to about 6" height and 36" wide, right
above
> the passenger compartment.

You want a "scoop" of sorts just above the roofline, right above the
rear
window?  I don't think that will really gain you a whole lot.  Your best
bet
is to measure air pressure at speed at various point where you could
place
an intake scoop.

A friend of mine at school here has an MR2 with a sunroof.  If he
un-latches
the sunroof, at 55 mph it will intermittently pop-up in back, due to low
air
pressure above the roof of the car.  If that's the case, you might not
get
ANY "ram-air" effect with a roof-mount scoop due to decreased air
pressure
at speed.

I'll try to find the link, but I think it was the Australian AutoSpeed
website that recently did an article on placing a pressure switch at
various
points on a vehicle and measuring the speed at which pressure was
reached to
turn the switch on.  Choosing the point on the car that turned the
switch on
at the lowest vehicle speed is the point where most pressure would be
generated at higher speed (assuming a bunch of things, but for drivable
speeds it's likely true).

Craig Dotson
crdotson at vt.edu
2002 VT FormulaSAE

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