[DeTomaso] Has anyone researched hood vent designs?
Dave Londry
davel at emspace.com
Fri Aug 5 13:57:23 EDT 2016
That is very interesting Mike.
I have forgotten to latch the hood (6143) a couple of times and it does
not lift off at speeds up to 75mph.
The only changes on the topside are the removal of the L bumper and the
addition of the hibachi grill.
The lower side has a dam but I'm not sure it has much aero effect.
It is almost 6" clear of the road.
dave
On 2016-08-04 9:05 PM, Ken Green via DeTomaso 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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-------------- next part --------------
That is very interesting Mike.
I have forgotten to latch the hood (6143) a couple of times and it does
not lift off at speeds up to 75mph.
The only changes on the topside are the removal of the L bumper and the
addition of the hibachi grill.
The lower side has a dam but I'm not sure it has much aero effect.
It is almost 6" clear of the road.
dave
On 2016-08-04 9:05 PM, Ken Green via DeTomaso 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 [1]<detomaso at server.detomasolist.com>
To: [2]julian_kift at hotmail.com; [3]tecnosound at hotmail.com;
[4]rkunishige at hotmail.com; [5]scottcouchman at yahoo.com;
[6]detomaso at server.detomasolist.com; [7]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, [[8]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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