<VV> Custom Fans

[RoboMan91324 at aol.com]

Mark,
 
Exactly right.  Both theory of fluid dynamics and  experimental data show 
that at some point, an increased differential in  pressure through a nozzle 
(cooling fins) has no increase in flow and can  actually lead to a decrease 
in flow.
 
Some who just knee-jerk state that the fans are inadequate  have not 
thought the subject through or in some cases are parroting others in an  attempt 
to seem knowledgeable.  When they parrot others who have had  success with 
fan/pulley modifications they usually do not understand the  specific 
conditions of those successful modifications.  To accept the  parrots as credible 
can lead to the inexperienced owner making modifications  that can damage 
their vehicles.
 
There are benefits to running a fan at a lower speed  ratio but the 
benefits are usually realized in applications where ambient  temperatures are 
fairly low and/or where the cars are driven at higher  speeds/engine RPM and/or 
in limited use.  In fact, some individuals  knowingly run their cars without 
a fan belt for gains in short duration  acceleration, but I don't think even 
the silliest among us would recommend this  for general street use.  But, 
you never know.  As stated above and  demonstrated with the cooling of your 
aircraft, at a certain RPM with the  standard set-up, the fan ceases to 
produce more flow through the engine.   With a different pulley ratio, the fan's 
flow will top out at a higher  engine speed but the top flow will not 
increase.  However, as they say,  there is no such thing as a free lunch.  The 
problem is that you lose air  flow at low RPM.  If you are pulling power at low 
engine RPM and/or with  high ambient temperatures, you need the higher fan 
RPM of a standard pulley  arrangement at that lower RPM.
 
The designers of the standard fan system knew the particular  needs of the 
Corvair far better than most if not all of us here on VV.   Yes, today, 
Engineers at GM and elsewhere have the benefit of powerful computers  and 
sophisticated software to model and tweek cooling systems before they take  the 
first cut of metal or produce a prototype casting.  However, even  without the 
software, those 50s and 60s Engineers had the benefit of many  decades of 
manual designs and real world experience to apply to our fans.   In addition, 
they had the benefit of labs, test equipment and personal to run  tests on 
various designs that we can only ream about.  They were not the  dummies 
some people here on VV seem to think they were.  Do you think that  the GM 
Engineers did not experiment with different pulley ratios, etc.?   Sure, if they 
were designing our Corvairs only for high  speed competition, they would 
have modified the pulleys and maybe the design of  the fan itself so that it 
did not top out at moderate-to-high RPM.  The  same thing if they assumed the 
Corvair would only be run in Minnesota in  winter.  However, the vast 
number of our cars are alternately run in hot  and cold weather as well as high 
and low RPM pulling high and low power and the  Engineers knew that.  Some 
also seem to think that most design parameters  were dictated solely by cost 
considerations.  While that was always a  consideration, in this case I doubt 
that a slightly different pulley ratio would  impact costs.  Further, a 
slightly different fan design would not reduce  material use and might actually 
increase it.
 
To say that the existing fan system is inadequate or  inefficient for the 
majority of Corvair use is silly.  The design was an  excellent compromise 
for all anticipated use of the cars.  Could it be  better?  Perhaps a minimal 
benefit could be had using today's design tools  but I doubt there would be 
a huge benefit for the general Corvair driver that  the pontificators seem 
to predict.  Of course, I am ignoring the  situation where major 
modifications might be made to many components of the  cooling system at the same time.  
This would include modifications to the  fan, pulleys, turkey roaster, 
cooling fins, etc.  However, considering how  well the majority of our Corvairs 
run, how many people would buy such a system  at what would probably be 
thousands of dollars plus installation and  modification costs.
 
With that said, we can realistically make modifications  to reduce the 
differential (back) pressure and increase flow through the  engine.  Anyone who 
has been on VV for a while has seen posts regarding  de-flashing the heads.  
This is the single most important thing we can do  to keep our engines 
cooler and more reliable.  When designing the cooling  system for our Corvairs, 
the GM Engineers assumed that the head castings would  look like their 
drawings throughout production.  In production and  especially after many 
thousands of castings produced from the same molds, the  air passages through the 
heads no longer resembled the original designs.   It would be foolish if you 
did not check your heads for flash and clean them up  as necessary 
especially if the engine is out of the car and the heads are  accessible.
 
I am not sure what benefit might be realized from an  intercooler in the 
general engine cooling system.  I do not think the air  between the fan and 
the engine fins has significantly elevated  temperature.  Other than that, I 
agree with everything you said,  Mark.
 
Just my opinion,
 
Doc
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
In a message dated 5/23/2012 8:21:31 A.M. Pacific Daylight Time,  
virtualvairs-request at corvair.org writes:

Message:  2
Date: Wed, 23 May 2012 07:19:56 -0700
From: Mark Durham  <62vair at gmail.com>
Subject: Re: <VV> custom fans
To:  "jvhroberts at aol.com" <jvhroberts at aol.com>,
"corvairgrymm at gmail.com" <corvairgrymm at gmail.com>,
"virtualvairs at corvair.org" <virtualvairs at corvair.org>
Message-ID:  <-6447027416945222160 at unknownmsgid>
Content-Type: text/plain;  charset=ISO-8859-1

Boys, boys, you cannot overturn the laws of physics.  You just do not seem 
to get that increased pressure will not substantially  increase cooling. 
Only so much air can move through the fins at the right  speed and pressure to 
cool. I used to work for a aircraft research and  development firm where we 
designed inlets for engine cowls, intercoolers, oil  coolers, etc., and a 
comparison can be had where a large inlet would be the  same as a more 
efficient fan in a Corvair. We actually had to decrease the  size of the opening at 
the inlet and slow down the air (reduce the pressure in  the air box over 
the engine, to get efficient cooling thru the fins. More  pressure brought on 
turbulent flow which caused hot spots. The Corvair stock  fan is a mass 
production design and does the job for production engines. A  fancier design 
may save some hp for drivers, but adding more pressure might  have the 
opposite of the intended effect. If you really want more cooling then  install a 
intercooler, move the oil cooler and put a fan on it or redirect the  outlet 
air away from the lower shroud area, and then realize that the turbo'd  
engines run hotter ( but at equivalent temps turbo'd aircraft engines run, I  say 
this because I consider the temps to be normal) (and if yours is  
consistently overheating, there is something wrong somewhere) and will last a  
shorter life span. Also use the best synthetic oil. Mark Durham

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