<VV> cooling horsepower

[Crawford Rose]

I posted the link to the more efficient 911 fan to the group. Hopefully someone can experiment and let us know the results of actually using that design on the Vairs.  I don't know if more efficient design can overcome the horsepower pumping requirements.
Crawford
  ----- Original Message ----- 
  From: JVHRoberts at aol.com<mailto:JVHRoberts at aol.com> 
  To: crawfordrose at msn.com<mailto:crawfordrose at msn.com> ; virtualvairs at corvair.org<mailto:virtualvairs at corvair.org> 
  Sent: Wednesday, July 13, 2005 8:34 PM
  Subject: Re: <VV> cooling horsepower


  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