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ʎpunq qoq
Joined: Jan 2014
Posts: 604
Total Cats: 202
From: Western Australia
Ignore them all...
The pressure zone at the base of the windscreen does exist when you are running on a race track at decent speeds. However, at lower speeds there isn't enough airflow to make much difference in pressure, especially given the airflow isn't directly passing over the car from front to back like on a track. My guess is that the radiator fan will be making a larger pressure differential than the airflow over the windscreen. Just make sure you run the stock under-tray at least.
No one has actually done any testing at slower speeds so here is your chance to prove them wrong. Do a couple of runs back to back with the hood down and up and datalog coolant temps and post the results. If you're really keen add a couple of tethers along the trailing edge of the bonnet and see which way they go. If they get sucked into the bonnet you know you're wrong.
I personally don't like the lifted hood, but hey if you like the look, run it.
The pressure zone at the base of the windscreen does exist when you are running on a race track at decent speeds. However, at lower speeds there isn't enough airflow to make much difference in pressure, especially given the airflow isn't directly passing over the car from front to back like on a track. My guess is that the radiator fan will be making a larger pressure differential than the airflow over the windscreen. Just make sure you run the stock under-tray at least.
No one has actually done any testing at slower speeds so here is your chance to prove them wrong. Do a couple of runs back to back with the hood down and up and datalog coolant temps and post the results. If you're really keen add a couple of tethers along the trailing edge of the bonnet and see which way they go. If they get sucked into the bonnet you know you're wrong.
I personally don't like the lifted hood, but hey if you like the look, run it.
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Ignore them all...
The pressure zone at the base of the windscreen does exist when you are running on a race track at decent speeds. However, at lower speeds there isn't enough airflow to make much difference in pressure, especially given the airflow isn't directly passing over the car from front to back like on a track. My guess is that the radiator fan will be making a larger pressure differential than the airflow over the windscreen. Just make sure you run the stock under-tray at least.
No one has actually done any testing at slower speeds so here is your chance to prove them wrong. Do a couple of runs back to back with the hood down and up and datalog coolant temps and post the results. If you're really keen add a couple of tethers along the trailing edge of the bonnet and see which way they go. If they get sucked into the bonnet you know you're wrong.
I personally don't like the lifted hood, but hey if you like the look, run it.
The pressure zone at the base of the windscreen does exist when you are running on a race track at decent speeds. However, at lower speeds there isn't enough airflow to make much difference in pressure, especially given the airflow isn't directly passing over the car from front to back like on a track. My guess is that the radiator fan will be making a larger pressure differential than the airflow over the windscreen. Just make sure you run the stock under-tray at least.
No one has actually done any testing at slower speeds so here is your chance to prove them wrong. Do a couple of runs back to back with the hood down and up and datalog coolant temps and post the results. If you're really keen add a couple of tethers along the trailing edge of the bonnet and see which way they go. If they get sucked into the bonnet you know you're wrong.
I personally don't like the lifted hood, but hey if you like the look, run it.
The fact that you didn't see it?
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ʎpunq qoq
Joined: Jan 2014
Posts: 604
Total Cats: 202
From: Western Australia
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I did. I used a manometer at a bunch of different speeds. Not drifting though. Although miniscule in psi. There was always positive pressure at the base of the winshield. Miniscule psi could still be a tremendous amount of CFM.
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ʎpunq qoq
Joined: Jan 2014
Posts: 604
Total Cats: 202
From: Western Australia
The windscreen base will always cause a low pressure zone with forward movement. That doesn't mean that air in the engine bay isnt at a higher pressure though. You need to measure both sides of the bonnet to see which way air will flow.
My guess is that at lower speeds the engine bay is at a higher pressure due to the mouth and radiator fan than the base of the windscreen. At what speed it switches over is anyones guess but I figure its somewhere between 10 and 40 mph.
My guess is that at lower speeds the engine bay is at a higher pressure due to the mouth and radiator fan than the base of the windscreen. At what speed it switches over is anyones guess but I figure its somewhere between 10 and 40 mph.
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This thread reminds me of my local autocross. Three years ago, one guy was frantically spraying his tires and wheels after a run. He explained to me that he was "stopping his tires from heat cycling ", and that he didn't want the tires to overheat. I started to wonder if he understood what a cycle was. Then I asked if I could measure the temp of his tires after a run. He agreed to let me and I measured across the tire width.
Run 2: tires were 25 degrees under operating temp. Scratched his head and ran another lap without watering his tires.
Run 3: tires were still 5-10 degrees under temp. He had run his two fastest times of the day, with still slightly under temp tires.
Run 4: He couldn't take it and had to spray his tires, just had to. Ran slower, blamed on driving.
Two years later that same dude is still watering his wheels and tires.
Moral of the story: You can lead a horse to water, but you can't make them drink.
Run 2: tires were 25 degrees under operating temp. Scratched his head and ran another lap without watering his tires.
Run 3: tires were still 5-10 degrees under temp. He had run his two fastest times of the day, with still slightly under temp tires.
Run 4: He couldn't take it and had to spray his tires, just had to. Ran slower, blamed on driving.
Two years later that same dude is still watering his wheels and tires.
Moral of the story: You can lead a horse to water, but you can't make them drink.
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This thread reminds me of my local autocross. Three years ago, one guy was frantically spraying his tires and wheels after a run. He explained to me that he was "stopping his tires from heat cycling ", and that he didn't want the tires to overheat. I started to wonder if he understood what a cycle was. Then I asked if I could measure the temp of his tires after a run. He agreed to let me and I measured across the tire width.
Run 2: tires were 25 degrees under operating temp. Scratched his head and ran another lap without watering his tires.
Run 3: tires were still 5-10 degrees under temp. He had run his two fastest times of the day, with still slightly under temp tires.
Run 4: He couldn't take it and had to spray his tires, just had to. Ran slower, blamed on driving.
Two years later that same dude is still watering his wheels and tires.
Moral of the story: You can lead a horse to water, but you can't make them drink.
Run 2: tires were 25 degrees under operating temp. Scratched his head and ran another lap without watering his tires.
Run 3: tires were still 5-10 degrees under temp. He had run his two fastest times of the day, with still slightly under temp tires.
Run 4: He couldn't take it and had to spray his tires, just had to. Ran slower, blamed on driving.
Two years later that same dude is still watering his wheels and tires.
Moral of the story: You can lead a horse to water, but you can't make them drink.
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Jun 8, 2016, 03:40 AM
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Reason: douche the spammer
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