<VV> cooling horsepower

[JVHRoberts at aol.com]

Hence the reason for an EFFICIENT fan. The Corvair fan at high airflows and  
static pressures is just beating the air up mostly. 
So, to run a calculation quickly, the specific heat of air is .241  
BTUs/pound/ºF. The density of air at STP is about 13 cubic feet per pound.  So...
At 1850 CFM, that's 142 pounds per minute, or the equivalent of 34 pounds  of 
water per minute. Assuming there's as much HP going out the crank as the  
cooling system, a reasonable assumption, 100 HP equals 4240 BTUs per minute.  
That's going to produce a temperature rise of 125 degrees F, assuming good  heat 
transfer. Usually on air cooled engines the heat transfer is pretty poor,  so, 
on a 100 degree day, the air leaving the engine, assuming the exhaust logs  
don't put any heat in there, is 225ºF. Given the poor heat transfer, expect the 
 heads to be at least 100ºF warmer than that! Already it's easy to see things 
are  marginal. 
OK back to the other air cooled flat 6. 911 engines make WAY more power,  use 
less fan HP, and stay cool. There's a message in there somewhere... Namely,  
get a MUCH better fan! You can't get much worse!
 
John
 
In a message dated 7/13/2005 8:47:07 A.M. Eastern Standard Time,  
crawfordrose at msn.com writes:

You may  all recall the discussion of the cooling sufficiency of the stock  
system.  I went back to read the SAE papers and the methodology that they  
used. The data was based on the research that Chevrolet performed that it  takes 
18 cubic feet of air  per minute per rated horsepower in 100 degree  ambient 
temps.  The airflow of the cooling system was 1850 cubic feet per  minute at 
4000 rpm.  Peak horsepower of 80 hp requires 1440 cubic  feet.  Curiously, that 
is similar to the rating of the later magnesium  fan's output but as far as the 
original design of the cooling system, it is  plain that 1850 cubic feet is 
adequate for the original engines by more than  twenty percent.  The math would 
indicate that 1850 cubic feet is  sufficient to cool to 102 horsepower. 
Therefore, the goal for 180 hp turbo  owners would have to be a implement a design 
that yielded at least 3240 cubic  feet per minute to enable sustained max 
output. That is a lot of air; more  than twice the output of the magnesium design 
that 180s rely upon.  I  think that the fan would drain significant additional 
horsepower to drive that  much air through the cylinders at 4000  rpm.
Crawford