Bonnet raisers
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Bonnet raisers
Why do people think fitting bonnet raisers helps with under bonnet temps?
Okay sitting in traffic yes but not driving along at 60-70mph
What are peoples thoughts on it?
Okay sitting in traffic yes but not driving along at 60-70mph
What are peoples thoughts on it?
#4
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Originally Posted by BigMouthBillyBass
several cries of "oi mate your bonnets open!"
is probably the only difference your going to see
is probably the only difference your going to see
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Re: Bonnet raisers!
Originally Posted by bigad4x4
Why do people think fitting bonnet raisers helps with under bonnet temps?
Okay sitting in traffic yes but not driving along at 60-70mph
What are peoples thoughts on it?
Okay sitting in traffic yes but not driving along at 60-70mph
What are peoples thoughts on it?
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i rasied my saff rear of the bonnet as i worried about the temp sometimes and now the air though the heater is a lot cooler so i would have to say yes
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Re: Bonnet raisers!
Originally Posted by THEYGOTMETOO
Originally Posted by bigad4x4
Why do people think fitting bonnet raisers helps with under bonnet temps?
Okay sitting in traffic yes but not driving along at 60-70mph
What are peoples thoughts on it?
Okay sitting in traffic yes but not driving along at 60-70mph
What are peoples thoughts on it?
he too said basically they were crap, how is the hot air going to escape
from under the bonnet when the wind force or whatever you call it is
holding it in the engine bay
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they draw the hot air from under the bonnet and let the air flow more freely towards the back off the engine bay, in a similar fashon to bonnet vents, hence dropping under bonnet temps! dont know how efficient they are though...
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erm have you ever seen a car in a wind tunnle the force of air comming at the front of the car hits the car and whirls round in a circle therefore pulling air from the back of the bonnet hot air is pulled out i think it will work at speeds
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Originally Posted by bai1ey
erm have you ever seen a car in a wind tunnle the force of air comming at the front of the car hits the car and whirls round in a circle therefore pulling air from the back of the bonnet hot air is pulled out i think it will work at speeds
#13
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Diagram is WRONG as it assumes(incorrectly) that the air pressure is EQUAL on both sides of the bonnet, IT IS NOT EQUAL.
The underbonnet air is at a lower pressure due to not being pressurised, to such a large extent as it is not MOVING AIR, such as that flowing over the car is, the air then hits the screen area(just before it) and creates a HIGH pressure wave that pushes air into heater inlet etc, it also pushes the air through he gap made by the bonnet raisers and is suctioned out from underneath the car where lower pressure also exists.
They DO make a difference, they can do noting other than make a difference as this is basic laws of physics/airflow/pressure.
Note this is why bonnet louvres/vents are at the front edge of the bonnet where the high pressure wave does not exist due to upright screen, but air intakes/scoops(scooby) are towards the rear of the bonnet.
Air acts in a very similar way to water, ie BOW WAVE of ship, ahead of the ship further the faster it goes.
tabetha
The underbonnet air is at a lower pressure due to not being pressurised, to such a large extent as it is not MOVING AIR, such as that flowing over the car is, the air then hits the screen area(just before it) and creates a HIGH pressure wave that pushes air into heater inlet etc, it also pushes the air through he gap made by the bonnet raisers and is suctioned out from underneath the car where lower pressure also exists.
They DO make a difference, they can do noting other than make a difference as this is basic laws of physics/airflow/pressure.
Note this is why bonnet louvres/vents are at the front edge of the bonnet where the high pressure wave does not exist due to upright screen, but air intakes/scoops(scooby) are towards the rear of the bonnet.
Air acts in a very similar way to water, ie BOW WAVE of ship, ahead of the ship further the faster it goes.
tabetha
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so the air would essentially push down teh back of the engine? rather than getting "sucked" out? you got any good info on this? i am very interested in the way things work and why they work! thanks!
#15
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a mate of mine fitted his first every time he drove it the coolant temp would reach 93 degrees
with the bonnet raisers on it now only reaches 85 degrees, so that is as much proof as i need to show they work a drop of 8 degrees
with the bonnet raisers on it now only reaches 85 degrees, so that is as much proof as i need to show they work a drop of 8 degrees
#18
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For any air to be sucked it would have to be in a vacuum, the air here has a high side in front of screen area as it acts as a brake(to forward motion), hence spoilers to "spoil"/smooth the airflow around such things.
The high pressure side will ALWAYS over come the low pressure side, as it exhibits more energy, so yes air would indeed flow downwards.
The whole principal of why F1 are shaped the way they are, and not like a bus!!
A pressure wave is created when any object moves through a gas or liquid, the wave MUST go somewhere, and the wave goes to the point of least resistance, it does not produce a vacuum but a low pressure side, so high pressure side will force the low pressure side, air asside.
This is the same principal of why certain cars have flat undersides, the air moving underneath will move a lot faster(lower pressure), so force downwards from higher pressure air acting on top will push it down for added grip, same as a rear spoiler.
tabetha
The high pressure side will ALWAYS over come the low pressure side, as it exhibits more energy, so yes air would indeed flow downwards.
The whole principal of why F1 are shaped the way they are, and not like a bus!!
A pressure wave is created when any object moves through a gas or liquid, the wave MUST go somewhere, and the wave goes to the point of least resistance, it does not produce a vacuum but a low pressure side, so high pressure side will force the low pressure side, air asside.
This is the same principal of why certain cars have flat undersides, the air moving underneath will move a lot faster(lower pressure), so force downwards from higher pressure air acting on top will push it down for added grip, same as a rear spoiler.
tabetha
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tabetha so what you are saying is that when you have bonnet raisers its not the hot air flowing out from under the bonnet but the cool air flowing into the engine bay.
is this what happens to RS Turbo bonnet vents then also. they let air in rather than letting air out....?
All sounds confusing to me!
is this what happens to RS Turbo bonnet vents then also. they let air in rather than letting air out....?
All sounds confusing to me!
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Originally Posted by TiB
Anyone want to explain how a non gravity spray gun works as surely this is the same effect?
Also as said earlier... i've seen it work for myself regardless of whether the heat goes up or down.
Lee
Also as said earlier... i've seen it work for myself regardless of whether the heat goes up or down.
Lee
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Originally Posted by nilrem
Originally Posted by bai1ey
erm have you ever seen a car in a wind tunnle the force of air comming at the front of the car hits the car and whirls round in a circle therefore pulling air from the back of the bonnet hot air is pulled out i think it will work at speeds
#29
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You don't need to let of any smoke bombs!!
Flow tests have already done this for you, vents work in different ways according to where they are, front mounted vents, are at a much lower pressure area, on an almost flat surface(bonnet) so hot air has no problem rising out of vents, as we get towards the screen area, there is a large upright, called the windscreen, which tries to resist being pushed through the air, this then MUST and does create a pressure(bow) wave in front of the car, the faster you go the further out in front of the car/screen it projects, as the pressure has nowhere to go becuase it is constantly being pushed (by car) it goes to point of least resistance which is downwards, this is one reason why your heater air flow gets better the faster you go WITHOUT the fan on.
The screen is pushing aside 00000's of litres of air every minute.
It is only theory that the air will in fact above a certain speed be pushed downwards, due to high pressure(air) spoiler(screen), but it must happen at a certain speed.
tabetha
Flow tests have already done this for you, vents work in different ways according to where they are, front mounted vents, are at a much lower pressure area, on an almost flat surface(bonnet) so hot air has no problem rising out of vents, as we get towards the screen area, there is a large upright, called the windscreen, which tries to resist being pushed through the air, this then MUST and does create a pressure(bow) wave in front of the car, the faster you go the further out in front of the car/screen it projects, as the pressure has nowhere to go becuase it is constantly being pushed (by car) it goes to point of least resistance which is downwards, this is one reason why your heater air flow gets better the faster you go WITHOUT the fan on.
The screen is pushing aside 00000's of litres of air every minute.
It is only theory that the air will in fact above a certain speed be pushed downwards, due to high pressure(air) spoiler(screen), but it must happen at a certain speed.
tabetha
#31
I can see how they work for sitting still, as it's a larger "outlet" and hot air rises, so it allows it to escape - but I do personally think they won't help when moving?
Why?
VORTEX
Similar in explanation to Tabetha basically, the effect is called a vortex - and I have seen many a big power V8 yank dragsters running air "ducts" that "faced the wrong way" - ie the opeing for the air to go into facing the screen, not the front of the car like you'd expect. Again the reason for this is the vortex created from the air hitting the screen.....
Why?
VORTEX
Similar in explanation to Tabetha basically, the effect is called a vortex - and I have seen many a big power V8 yank dragsters running air "ducts" that "faced the wrong way" - ie the opeing for the air to go into facing the screen, not the front of the car like you'd expect. Again the reason for this is the vortex created from the air hitting the screen.....
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Originally Posted by tabetha
You don't need to let of any smoke bombs!!
Flow tests have already done this for you, vents work in different ways according to where they are, front mounted vents, are at a much lower pressure area, on an almost flat surface(bonnet) so hot air has no problem rising out of vents, as we get towards the screen area, there is a large upright, called the windscreen, which tries to resist being pushed through the air, this then MUST and does create a pressure(bow) wave in front of the car, the faster you go the further out in front of the car/screen it projects, as the pressure has nowhere to go becuase it is constantly being pushed (by car) it goes to point of least resistance which is downwards, this is one reason why your heater air flow gets better the faster you go WITHOUT the fan on.
The screen is pushing aside 00000's of litres of air every minute.
It is only theory that the air will in fact above a certain speed be pushed downwards, due to high pressure(air) spoiler(screen), but it must happen at a certain speed.
tabetha
Flow tests have already done this for you, vents work in different ways according to where they are, front mounted vents, are at a much lower pressure area, on an almost flat surface(bonnet) so hot air has no problem rising out of vents, as we get towards the screen area, there is a large upright, called the windscreen, which tries to resist being pushed through the air, this then MUST and does create a pressure(bow) wave in front of the car, the faster you go the further out in front of the car/screen it projects, as the pressure has nowhere to go becuase it is constantly being pushed (by car) it goes to point of least resistance which is downwards, this is one reason why your heater air flow gets better the faster you go WITHOUT the fan on.
The screen is pushing aside 00000's of litres of air every minute.
It is only theory that the air will in fact above a certain speed be pushed downwards, due to high pressure(air) spoiler(screen), but it must happen at a certain speed.
tabetha
Where are these flow tests?? what car were they performed on?
Different cars have different aerodynamics yes/no?
Were these tests done on a car with raisers on as they will change the airflow angle to the screen yes/no?
I have tried them on a fiesta and they worked!! i will try them on the sierra to see if they work on that too.
Lee
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i would suggest that they do not work at speed as having the bonnet raised up in a differant plane to the shape of the front of the car will cause a vortex (rotating air), vortex's are likely to be higher in pressure than the flow of air also exiting the under bonnet, thus not allowing it exit, also the vortex combined with the wave due to the incline of the wind screen will completly change the air flow enough that you will get insufficient draw from any bonnet vent you mat have
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Originally Posted by nilrem
i see what you mean... so in reality cossy & turbo vents should idealy be the other way round, or just holes???
although they are closer to the front of the bonnet than the back where the least resistance is, but surely they were designed with the holes angled that way for a reason???
I always wondered why they faced that way
#37
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I put them on my car as had issues with act's and Grove / Ahmed told me to chop some out the bumber and stick them on don't care what it looks like apparently it helped alot
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i fitted bonnet raisers to my sapp and noticed a big difference in temps. i like the look but i fitted them for the reason of cooling cause its easier and cheaper than buying a vented bonnet or cutting up my old bonnet to fit vents