Most cowl induction hoods don't actualy work, the mid-70's Trans-Am shaker
scoop being a great example. It's just too damn far away from the
windshield to work. But logic hasn't stopped people from putting NACA ducts
all over cars, despite the fact that they don't work any better than any
other shape below ~130 mph at standard atmospheric conditions. Don't get me
wrong.. they look cool and I'd consider using them for aesthetic purposes.
Visualize it like this: You're driving in your LBC on a back country road
in the fall (it's almost that season!!). Imagine the path that a falling
leaf would follow as it passes over your car (OK, the car passes under the
leaf). It approximates the boundary of moving air over the car. Where the
air is moving (or being moved through as Einstein and Bernoulli would love
to discuss), it's pressure is lower
than where it is stationary. "Static" air only exists within a layer a few
inches thick in front of the windshield (on a car like the MGB w/ its
near-vertical glass) and in an even thinner layer on modern wind-tunnel cars
Think of the commercials where they show a stream of smoke being blown
over the car to emphasize its aerodynamic shape. The tiny margin between
the smoke and the car is the high-pressure zone from where a cowl would have
to ingest air.
The back of a hood on an MGB is right in that questionable area where I
wouldn't feel comfortable eyeballing whether it is a high or low pressure
zone. You could tape some pieces of string there and drive around and see
how they move. By default, raising the back of the hood will create a
turbulent area w/ different conditions from when the hood is flush.
James J.
-------Original Message-------
From: Larry list account
Date: Wednesday, August 20, 2003 4:27:40 PM
To: 'v8'
Subject: RE: was timing, now Engine Compartment Hot Air Exit
Near the bottom of the windshield equals high pressure. About
'windshield height' forward of the bottom of the windshield equals low
pressure. If you want to extract air from the engine compartment the
ducting needs to be near the forward portion of the hood.
The example of the hood being raised at the rear is effective for a race
car; but typically a roadster with minimal windshield. (cut down or a
small windscreen in front of the driver.)
Larry Hoy
[demime 0.99d.1 removed an attachment of type image/gif which had a name of
IMSTP.gif]
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