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@server.detomasolist.com> To: julian_kift@hotmail.com; tecnosound@hotmail.com; rkunishige@hotmail.com; scottcouchman@yahoo.com; detomaso@server.detomasolist.com; kenn_green@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, julian_kift@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 _______________________________________________ Detomaso Email List is not managed by POCA Posted emails must not exceed 1.5 Megabytes DeTomaso mailing list DeTomaso@server.detomasolist.com http://server.detomasolist.com/mailman/listinfo/detomaso To manage your subscription (change email address, unsubscribe, etc.) use the links above. Members who post to this list grant license to the list to forward any message posted here to all past, current, or future members of the list. They also grant the list owner permission to maintain an archive or approve the archiving of list messages. 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@server.detomasolist.com> To: julian_kift@hotmail.com; tecnosound@hotmail.com; rkunishige@hotmail.com; scottcouchman@yahoo.com; detomaso@server.detomasolist.com; kenn_green@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@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 _______________________________________________ Detomaso Email List is not managed by POCA Posted emails must not exceed 1.5 Megabytes DeTomaso mailing list [2]DeTomaso@server.detomasolist.com [webicon_gray.png] [3]http://server.detomasolist.com/mailman/listinfo/detomaso To manage your subscription (change email address, unsubscribe, etc.) use the links above. Members who post to this list grant license to the list to forward any message posted here to all past, current, or future members of the list. They also grant the list owner permission to maintain an archive or approve the archiving of list messages. References 1. mailto:julian_kift@hotmail.com 2. mailto:DeTomaso@server.detomasolist.com 3. http://server.detomasolist.com/mailman/listinfo/detomaso