<VV> Air Flow Question

RoboMan91324 at aol.com RoboMan91324 at aol.com
Sat Sep 12 22:49:31 EDT 2009


Jim,

I assume that your "string test" is the attachment of strings at the air 
intake with an assistant watching them while the car is in motion to see which 
way the air is flowing.  Is this correct?  If this is the case, I imagine 
that your results were ambiguous.  Whether or not there is a "natural" 
positive pressure at that location, you will have a "created" positive pressure 
due to the fan and it would be difficult to attribute the pressure to either 
the fan or the air flow characteristics of the car in the slip stream.  It is 
further complicated by the fact that the air flow through the engine and 
engine compartment is controlled by the thermostats and cooling air exhaust.  

Here is a suggestion that might work.  Take your lower shrouds off so the 
thermostats are out of the picture, so to speak.  Attach your strings at the 
intakes as before.  Get the car running at speed, preferably on the downside 
of a hill, then turn off the engine and coast so that the fan has no 
influence on the air flow and have your assistant view the strings.

My gut feel is that the pressure will be fairly neutral.  There will be a 
Bernoulli's Effect up top as well as some level of suction that will tend to 
draw air from the intake but there could also be a suction created from 
airflow under the car.

The bottom line is that you will probably not be able to rely on "natural 
flow" to remove heat from the radiator.  You should probably get a couple of 
robust fans designed for creating radiator flow.  You should probably get 
beefy units because you will not have the benefit of direct forced air like a 
front engine water pumper normally relies on.  Make sure you have enough 
amps for the additional power draw.  You should check with other v8 Corvair 
owners to see what they have done.  I believe that they mostly count on airflow 
from under the car.

Good luck,

Doc
1960 Corvette; 1961 Rampside; 1962 Rampside; 1964 Spyder coupe; 1965 
Greenbrier; 1966 Corsa turbo coupe; 1967 Nova SS; 1968 Camaro ragtop
~~~~~~~~~~~~~~~~~~~~~~~~~~
In a message dated 9/12/2009 2:50:45 PM Pacific Daylight Time, 
virtualvairs-request at corvair.org writes:

> Message: 7
> Date: Sat, 12 Sep 2009 13:45:09 -0700
> From: Jim Briggs <jim_a_b3 at hotmail.com>
> Subject: <VV> Air flow question
> To: virtual vairs <virtualvairs at corvair.org>,
>     <fastvair at yahoogroups.com>
> Message-ID: <COL116-W65FF7B88ECE19DCDE4731091E60 at phx.gbl>
> Content-Type: text/plain; charset="iso-8859-1"
> 
> 
> I'm trying to figure out if the air pressure over our LM air intakes 
> behind the rear glass is +positive or -negative and how much.  I've looked at 
> the pictures on AeroNed's site but they are not diffinitive. I've even tried 
> my own rudimentary string test.  Has there been any measurement testing 
> done out there? I'm trying to determine which way to flow the air through the 
> horizontal radiator above the transaxle on my rear engine V8 project. It's 
> obvious that with a closed engine compartment our air cooled Vairs can 
> "pull" enough air for cooling but I'm trying to figure out if there is 
> significant positive pressure aiding the cooling fan?
> 
> Thanks for any help!
> Jim Briggs
> 65 coupe & sedan
> 66 Corsa V8


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