[s-cars] Fans on the dyno

[Mark Strangways]

I will not argue with your math, not one bit.
But I would not be trying to stop my , or anyone else's seized VC fan. Not with a glozed hand, not with a block of wood.
I don't remember what other changes where made between run's but it wasn't significant.
I think I just removed the fan and adjusted the water injection.

Maybe my only comments to your deductions is that a mechanical fan's power requirements are a function of it's RPM. Higher RPM = higher load ? No ?

Just how many HP does it take to turn the alternator shaft when the load on it is 95% ?

Mark
  ----- Original Message ----- 
  From: QSHIPQ at aol.com 
  To: StrangConst at rogers.com ; petergolledge at gmail.com ; Djdawson2 at aol.com ; fastscirocco_2000 at yahoo.com ; s-car-list at audifans.com 
  Sent: Saturday, May 12, 2007 9:28 AM
  Subject: Fans on the dyno


  I don't think it was a measureable part of it at all Mark!  You can stop that fan with your hand in a glove when the VC is locked up, and it will slip on the belt.  I doubt it's even 2 hp (see math below). 

  The reason for VC fans is to keep the load off the electrical system.  As a rule, engine power to drive a fan is more efficient than electrical power.  The narrower the pitch of the fan (and S shaped fans are less efficient at moving air) the less load it will have on the motor/engine.   The smaller fan blade depth, the less efficient it will be as well.  But, mechanical fans also tend to move more air for a given rpm, because they don't overload the motor.  For more on this look at flow vs load draw on Spa electric fan specification sheets.

  Prior to the v8 then Scar, cooling was using a 70amp driven electric 7 blade fan in the 5000/200.  12 x 70 = 840watt fan.  That sucks up a lot of alternator capacity.  Add in the S car aux fan 300watter, you have potentially 1140watts of draw using that same app. 1140/12 = 95 amp draw on a 110amp alt, no other load counted!

  Now, if we know that 1 hp = 750watts, then that old 840 watt fan is 1.12hp,  Mark, call the one in the S car double the old 200 fan, at 2 horsepower, it's the equivelent of a 1600watt fan.  At that, it shouldn't need the 300w aux fan.  No, I rather suspect that the stock fan is less than 1hp, as Golledge notes, it's not even a driven part (it's off the back of the belt)

  Those of us familiar with the older monster 7 blade fans, would call the S car VC driven fan a joke in comparison to the old 200 7 blade style.

  Continuing the argument, for 40hp = 30,000 watt fan.  Saying that the S car mechanical fan is 30 times the air of the old 840 watt audi fan, seems a bit unreal to me.

  I have a lot of my Landcruiser library full of information on switching from the monster helicopter blade to electrics, including research into the electro coupling mechanical fan.   I have yet to find a electric setup I'm comfortable with to equal the cooling potential, and would rather see the electro-mechanical coupling conversion come into play, it is the future of all automotive and truck fans IMO.

  Scott Justusson
  In a message dated 5/11/2007 7:28:18 P.M. Central Standard Time, StrangConst at rogers.com writes:
    Like I said later, mine was seized so that would actually suck the power if it need the cooling or not.
    I did  measure a 40 HP gain, I cannot say 100% it was due to just the fan, but I really have to believe that was a large portion of it

    Mark 






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