[DeTomaso] Has anyone researched hood vent designs?

Fri Aug 5 07:05:40 EDT 2016

The best situation is to remove stagnant boundary and laminar flow issues, not how much air can been crammed in to the cars open ports but how the air is managed and removed. Make your air work for your benefit! 
 Frontal floating at speed is the net result of too much pressure under the car not velocity air lift on top.
The air dynamics are at its highest between dynamic -car- and static -ground- items. Remember your radiator is trying to exhaust air into the high pressure that is being jammed into the upward pointed noses underside. Does not work well, Mike and Ken are correct, hood vents work great and at all speeds as long as it is prior designed managed. But all cars benefit the most from an air dam/spoiler device so to redirect the frontal air weight to around the car or through grill to the now new low pressure zone under trunk. Remember a high speed laminar flow over your hood vents will not work if you can not get in enough volume to shove the column of air out. Hood air pressures and flows do not matter below 115+- mph or so. So does any of this matter if you stay below a high speed?
So place on a spoiler or dam, seal up the radiator/condenser so no air will flow around them and put on a hood vent if you desire. Your front end lift will slow down as you will redirect prior dead under car air to properly flow through heat exchangers and out of car. Aero dynamics only come into real force play above 70 or so.
Jeff

Jeff Cobb- I pad
W-225-343-7525
C-225-907-4514

www.LiveOakConcours.org

On Aug 4, 2016, at 11:05 PM, Ken Green via DeTomaso <detomaso at server.detomasolist.com> wrote:

>   People who have gone seriously fast all seem to agree that proper hood
>   vents make a big difference, especially over about 140.  As far as
>   pressure on the hood building, the air flow through the grill may grow
>   even more with speed, and the pressure difference is the real issue.  I
>   looked at a lot of closed wheel, mid engine, race cars, and virtually
>   all of them vent the radiators through the hood area.
>   Ken
>     __________________________________________________________________
> 
>   From: Mike Drew via DeTomaso <detomaso at server.detomasolist.com>
>   To: julian_kift at hotmail.com; tecnosound at hotmail.com;
>   rkunishige at hotmail.com; scottcouchman at yahoo.com;
>   detomaso at server.detomasolist.com; kenn_green at yahoo.com
>   Sent: Thursday, August 4, 2016 8:55 PM
>   Subject: Re: [DeTomaso] Has anyone researched hood vent designs?
>     In a message dated 8/2/16 7 55 50, [1]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
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