[DeTomaso] Has anyone researched hood vent designs?

[MikeLDrew at aol.com]

In a message dated 8/2/16 7 55 50, julian_kift at hotmail.com writes:


> Hood vents are a great way to provide additional cooling in traffic, but 
> perhaps  limited value at high speed when the front of the hood becomes a 
> high pressure area. Now you have opposing forces at play and at speed 'x'  
> the pressure is likely enough to overcome that produced by the radiator fans 
> (I imagine that 'x' would not be excessively high, perhaps even highway 
> cruising speed). So outside air now reverse enters the hood vents or at a 
> minimum restricts fan flow resulting in air that is forced under the car i.e. 
> back to the original Ford design concept. A Gurney lip on the frontal edge 
> of hood vents would help create a low pressure area, but I still believe 
> the air from the radiators will ultimately be forced under the car at some 
> speed now x+y.
> 

>>>I don't know about high triple-digit speeds, but the hood is a 
low-pressure area at speeds typically seen on the road (even low triple-digit 
speeds).   You can test this for yourself by simply unlatching the hood and going 
for a drive.   At freeway speeds, it will 'float' an inch or two above the 
latch, as vacuum from above (probably aided by pressure from below) lifts it 
slightly.

I don't know what, if any effect might be realized by introducing hood 
vents with all other things being equal.   Providing a path for air to exit 
through the hood rather than pushing up on the underside of it might be a thing?

(Geoff Peters had a very thin carbon fiber hood, with vents, on his GT5, 
and he found that at high speeds, it would deform so much by lifting in the 
center, that the pin would move forward and pop out the front side of the 
latch and then the hood would fly open and hover a few inches above the latch!)

An air dam, particular a proper Gr4/GT5 air dam, provides meaningful 
downforce and probably helps prevent air from underneath from pressing up on the 
underside of the hood, as others have mentioned....

If you look at the GT40, the early cars came with two deep triangular hood 
vents, while the later ones came with a single very large vent, which was 
undoubtedly far more effective.

Having said all of that, I've run my car at 130+ mph on the track with a 
simple, small GTS mini air dam and no hood vents, and the car ran at 180 
degrees with not a bit of front-end lift.   I wouldn't assert that the front end 
would be similarly planted at 200 mph, but then again, I have no intention 
of going anywhere near 200 mph so it's completely academic....

Mike
-------------- next part --------------
   In a message dated 8/2/16 7 55 50, julian_kift at hotmail.com writes:

     Hood vents are a great way to provide additional cooling in traffic,
     but perhaps  limited value at high speed when the front of the hood
     becomes a high pressure area. Now you have opposing forces at play
     and at speed 'x'  the pressure is likely enough to overcome that
     produced by the radiator fans (I imagine that 'x' would not be
     excessively high, perhaps even highway cruising speed). So outside
     air now reverse enters the hood vents or at a minimum restricts fan
     flow resulting in air that is forced under the car i.e. back to the
     original Ford design concept. A Gurney lip on the frontal edge of
     hood vents would help create a low pressure area, but I still
     believe the air from the radiators will ultimately be forced under
     the car at some speed now x+y.

   >>>I don't know about high triple-digit speeds, but the hood is a
   low-pressure area at speeds typically seen on the road (even low
   triple-digit speeds).  You can test this for yourself by simply
   unlatching the hood and going for a drive.  At freeway speeds, it will
   'float' an inch or two above the latch, as vacuum from above (probably
   aided by pressure from below) lifts it slightly.
   I don't know what, if any effect might be realized by introducing hood
   vents with all other things being equal.  Providing a path for air to
   exit through the hood rather than pushing up on the underside of it
   might be a thing?
   (Geoff Peters had a very thin carbon fiber hood, with vents, on his
   GT5, and he found that at high speeds, it would deform so much by
   lifting in the center, that the pin would move forward and pop out the
   front side of the latch and then the hood would fly open and hover a
   few inches above the latch!)
   An air dam, particular a proper Gr4/GT5 air dam, provides meaningful
   downforce and probably helps prevent air from underneath from pressing
   up on the underside of the hood, as others have mentioned....
   If you look at the GT40, the early cars came with two deep triangular
   hood vents, while the later ones came with a single very large vent,
   which was undoubtedly far more effective.
   Having said all of that, I've run my car at 130+ mph on the track with
   a simple, small GTS mini air dam and no hood vents, and the car ran at
   180 degrees with not a bit of front-end lift.  I wouldn't assert that
   the front end would be similarly planted at 200 mph, but then again, I
   have no intention of going anywhere near 200 mph so it's completely
   academic....
   Mike