carl0s Posted October 27, 2007 Share Posted October 27, 2007 We went to Rusholme for a curry last night. One of the chaps who worked there had a black Impreza WRX. Nice car, better in black than other colours anyway. He'd fitted a roof scoop though, and I told him it looked like a black-cab thing. Just like this: http://www.toucantraveller.com/taxi.jpg He said that this scoop was very beneficial because at speed it caused the rammed air to pressurise, and directed this pressurised air at the rear spoiler, resulting in much improved downforce. I didn't want to appear to facetious, I'm already bad enough after a few drinks, so I just said I thought he should think about testing that theory in a wind tunnel. Anyhoo, was he right after all? I'm not good with physics, but my instinctive thoughts are that it doesn't work like that at all, and simply causes a major drag and slows the car down. I'd have thought angling the entire roof of the car in the reverse angle of his scoop would work better. His scoop might provide some downforce if he was driving in reverse though. Here's an illustration I made http://www2.css-networks.com/downforce.jpg What do you more intelligent folks reckon? Link to comment Share on other sites More sharing options...
Havard Posted October 27, 2007 Share Posted October 27, 2007 Makes sense to me! Where can I get one?? H. Link to comment Share on other sites More sharing options...
Daston Posted October 27, 2007 Share Posted October 27, 2007 roof scoops do work some rally cars and gt cars use them on the track. However I think its also to create central downforce as well as direct air to the rear spoiler Link to comment Share on other sites More sharing options...
carl0s Posted October 27, 2007 Author Share Posted October 27, 2007 roof scoops do work some rally cars and gt cars use them on the track. However I think its also to create central downforce as well as direct air to the rear spoiler I thought that was to cool the engine? Link to comment Share on other sites More sharing options...
Daston Posted October 27, 2007 Share Posted October 27, 2007 Yeah the mid engine cars it does, however I think the evo rally car has a roof scoop. I will get some pics Link to comment Share on other sites More sharing options...
Daston Posted October 27, 2007 Share Posted October 27, 2007 http://www.motionmotorsport.co.za/images/rueda_mitsu_20_mp_big.jpg Link to comment Share on other sites More sharing options...
carl0s Posted October 27, 2007 Author Share Posted October 27, 2007 http://www.motionmotorsport.co.za/images/rueda_mitsu_20_mp_big.jpg http://www.motionmotorsport.co.za/images/rueda_mitsu_20_mp_big.jpg Trust me, that thing isn't directing anything at the rear spoiler. Google says it's there to cool the interior. Link to comment Share on other sites More sharing options...
Daston Posted October 27, 2007 Share Posted October 27, 2007 nope but I would say its increasing the central downforce. Its got to be doing something??? Wheres Chris when you need him? Link to comment Share on other sites More sharing options...
carl0s Posted October 27, 2007 Author Share Posted October 27, 2007 nope but I would say its increasing the central downforce. Its got to be doing something??? It's cooling the interior apparently. No A/C in a rally car. Now back to the Impreza with its black cab roof scoop Digsy.. IanC.. where are you? Link to comment Share on other sites More sharing options...
Daston Posted October 27, 2007 Share Posted October 27, 2007 http://www.socalrally.com/car/audi_launch.jpg Ahh this one has a hole at the back Link to comment Share on other sites More sharing options...
TLicense Posted October 27, 2007 Share Posted October 27, 2007 nope but I would say its increasing the central downforce. Its got to be doing something??? Wheres Chris when you need him? I wouldn't have thought it's doing much to aid central downforce. If anything the most you'll get from it is a disruption of flow over the roof which will effectively remove the amount of body lift. If it created any significant reduction in body lift by doing this though, it would span the entire way across. The idea about it speeding flow through it and aiding the rear wing is also a bit flawed. It would have to be pretty close to the wing to have any effect. Any reduction in dynamic air pressure will be long gone due to the infinite expansion behind the scoop, and the 1.5-2metres between the scoop and wing. My understanding is that they just aid interior cooling. Link to comment Share on other sites More sharing options...
Daston Posted October 27, 2007 Share Posted October 27, 2007 good point but what about the ones that dont actually sit on the roof? There is one car (cant think of it at the moment) that has a long roof scoop on stalks Link to comment Share on other sites More sharing options...
michael Posted October 27, 2007 Share Posted October 27, 2007 Basically your man wants to be a WRC driver but doesn't have the brain capacity to read up what he's sticking to the car - it's just a cover for the naff looking cabin cooling vent they fit to some of the models normally, on the rally cars it probably aids cooling and is more aerodynamic than the standard one but on on his it probably vents out the back because he doesn't have the hole in the roof. If it didn't the air being forced into it would probably pull it off, I guess some functional ones might do the same for when the roof hatch is shut. Link to comment Share on other sites More sharing options...
carl0s Posted October 27, 2007 Author Share Posted October 27, 2007 I'll show all this to Amanda when she wakes up. I kept saying "stop entertaining the idiots" Link to comment Share on other sites More sharing options...
grahamc Posted October 27, 2007 Share Posted October 27, 2007 I always thought it was to aid with pressurising the cabin. Link to comment Share on other sites More sharing options...
carl0s Posted October 27, 2007 Author Share Posted October 27, 2007 vents out the back because he doesn't have the hole in the roof. If it didn't the air being forced into it would probably pull it off, I guess some functional ones might do the same for when the roof hatch is shut. That explains the Audi Quattro one that vents out the back then Link to comment Share on other sites More sharing options...
Ewen Posted October 27, 2007 Share Posted October 27, 2007 I would have thought rear wings would work best with a clean uninterupted flow of air, the roof scoop must be disturbing the air to the rear wing surely. As above, I thought the roof scoop on rally cars was air to the cabin, roof scoops on a GT car was air to a mid mounted engine (NSX). There is more convincing science applied to the row of small shark fins on the aft edge of the roof on some Evos etc, which is supposed to aid air flow to the rear wing. Link to comment Share on other sites More sharing options...
bluecoup Posted October 27, 2007 Share Posted October 27, 2007 if the scoop was ducted to the spoiler maybe but as soon as the so called pressurise air leaves scoop to the atmosphere its no longer pressurised. pfft scooby drivers, got a compresser ? try it on max with just a blowing attachment put it on the front of the roof facing backwards, how much of this air makes it to the spoiler Link to comment Share on other sites More sharing options...
juanchan Posted October 27, 2007 Share Posted October 27, 2007 I would have thought rear wings would work best with a clean uninterupted flow of air, the roof scoop must be disturbing the air to the rear wing surely. As above, I thought the roof scoop on rally cars was air to the cabin, roof scoops on a GT car was air to a mid mounted engine (NSX). There is more convincing science applied to the row of small shark fins on the aft edge of the roof on some Evos etc, which is supposed to aid air flow to the rear wing. I was thinking about those shark fin things. My understanding of them is that they act like vortex generaters on plane wings - they induce turbulence into the flow, which allows the flow to remain attached to the surface of the car for longer, which should in theory cause more flow down the rear windscreen, and onto the rear wing. Which should create more downforce. Link to comment Share on other sites More sharing options...
Lewis Posted October 27, 2007 Share Posted October 27, 2007 I was thinking about those shark fin things. My understanding of them is that they act like vortex generaters on plane wings - they induce turbulence into the flow, which allows the flow to remain attached to the surface of the car for longer, which should in theory cause more flow down the rear windscreen, and onto the rear wing. Which should create more downforce. Maybe....you'd look like a tit though Link to comment Share on other sites More sharing options...
juanchan Posted October 27, 2007 Share Posted October 27, 2007 Maybe....you'd look like a tit though Eh? I don't geddit? Link to comment Share on other sites More sharing options...
Cass Posted October 27, 2007 Share Posted October 27, 2007 So whats this Chav's excuse then?.Surley he doesn't need downforce or is it there for somewhere to hang the pretty coloured lights he just got from Pound Strechers At least he got one thing right total Mutant Link to comment Share on other sites More sharing options...
Lewis Posted October 27, 2007 Share Posted October 27, 2007 Eh? I don't geddit? Link to comment Share on other sites More sharing options...
grahamc Posted October 27, 2007 Share Posted October 27, 2007 http://i140.photobucket.com/albums/r25/monstermodz/Evo9in1SharkFin.jpg Ok, I am not sure if its the sunroof or the number of them, but that just looks wrong Link to comment Share on other sites More sharing options...
juanchan Posted October 27, 2007 Share Posted October 27, 2007 http://prettyphotobucketpictureofanevo I get it now - I was thinking about what the fins did, not thinking of sticking them on my Supra! That would be silly Link to comment Share on other sites More sharing options...
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