Smartripper
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| posted on 21/1/06 at 08:50 PM |
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Bonnet Vents
Hello,
Because a ZX12-R engine is very hot by nature.
Will it help i've i cut some bonnet vents at this space ???
They will be 7 x 4 cm big.
Smartripper
 
Rescued attachment klaar.jpg
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rusty nuts
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| posted on 21/1/06 at 09:09 PM |
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Yeah , cut the bushes down as well
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stevebubs
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| posted on 21/1/06 at 09:26 PM |
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Yes - will help with underbonnet temperatures
Will also help with the tendency a bonnet has to start to try and lift at high speeds - pressure will be released out the side rather than be kept in
the engine bay
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piddy
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| posted on 22/1/06 at 10:41 AM |
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Yes it will make a big differents. Another way is to wrap the exhaust that is under the bonnet in exhaust wrap stuff.
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Hellfire
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| posted on 22/1/06 at 11:10 AM |
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Heres a couple of things we did to get the temperature down on our ZX12
1 - Put Water Wetter in coolant
2 - Used expanding foam in nosecone, to direct all the air that enters the nosecone through the radiator
3 - Bonnet vents to allow hot air to escape. Like this
[img][/img]
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C10CoryM
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| posted on 22/1/06 at 05:23 PM |
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If you are trying to lower the coolant temp the best way is to properly exhaust the radiator.
You have to remember that all the air going into the rad has to get out somewhere.
Ideally you will have a sealed intake into the rad then route some ducting to the outside of the car ( the sides usually).
This will also lower your ambient underhood temp as well because all that hot rad exhaust is no longer underhood.
To further lower the ambient temps you use vents and heat wrapping.
Cheers.
[edit] added some pagebreak things to make it easier to read.
[Edited on 22/1/06 by C10CoryM]
"Our watchword evermore shall be: The Maple Leaf Forever!"
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stevebubs
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| posted on 22/1/06 at 05:53 PM |
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My only concern with putting the vents there is if something goes under the bonnet, you're going to get hot oil / steam vapours straight in the
face....especially with just a flyscreen for protection
Looks nice, though....
quote:
Originally posted by Hellfire
Heres a couple of things we did to get the temperature down on our ZX12
1 - Put Water Wetter in coolant
2 - Used expanding foam in nosecone, to direct all the air that enters the nosecone through the radiator
3 - Bonnet vents to allow hot air to escape. Like this
[img][/img]
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Hellfire
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| posted on 22/1/06 at 06:18 PM |
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It's surprising just how effective the aeroscreen is, at deflecting bugs and stuff over your head. Anything that does get through, meets the
second line of defence - The helmet visor. 
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Smartripper
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| posted on 22/1/06 at 06:27 PM |
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Thanks for all the advice, soo i'am going too make some holes in the bonnet then...
i don't like the idea off cutting holes in the fibreglass but with a good template and a router in think it will work out oke..
After that just black mesh behind it....
Smartripper
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02GF74
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| posted on 22/1/06 at 09:23 PM |
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what abouot fitting ali sheet to the underside of the engine bay to seal it? air comes in via nosecone, and then exits via the vents and tranmsision
tunnel or wouldthat be too restrictive?
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locost_bryan
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| posted on 23/1/06 at 01:35 AM |
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I'd be tempted to put vents at the front of the bonnet (side and top), with ducting behind the radiator to direct the air through them.
Have the vents at the rear as well to aid cooling the engine and exhaust. Allow some cool air to bypass the radiator and duct it into the engine
bay.
This would separate the radiator from the engine bay, and help to keep the engine cooler too.
Another bonus for vents on the top of the bonnet, is it improves the aero. All that trapped air trying to lift the bonnet is effectively pushing the
front of the car away from the ground! Venting it our the top (like Donkervoort do) should at least neutralise the lift, if not give some downforce
(it should also give less drag from all that turbulent under-bonnet air hitting the vertical footwells and being squeezed out under the floor!)
That's my theory anyway...
Bryan Miller
Auckland NZ
Bruce McLaren - "Where's my F1 car?"
John Cooper - "In that rack of tubes, son"
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C10CoryM
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| posted on 23/1/06 at 05:52 AM |
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The problem with no rad exhaust ducting is that all that air ends up stuck under the hood at speed and creates a high pressure area. This high
pressure area trys to lift the hood and the car creating lift. You need to either vent all that air, or keep if from getting there in the first
place.
Generally the air is ducted to the sides of the car because it doesn't affect the downforce of the car to blast all that air out the sides.
Ducting air under the car creates lift because you are again increasing air pressure under the car. Ducting it out the top is better, but it can
disturb the airflow over the car creating drag, probably not a big deal on a locost.
For the cooling aspect, any air going in, has to get out just as easy for optimal cooling to happen. Take a look at Lemans cars. Most of them have a
very small inlet in front, with massive exhaust ducts just behind the front wheels. They also duct the front diffuser and wheel wells there.
Ideally you should have the smallest inlet required, with oversized exhaust. Seal the bottom of the engine bay so no air gets in from underneath and
run small vents underhood just in case.
BTW, the vents on Hellfires car are not the best idea if you are running a full size windscreen. There is a high pressure area at the cowl (scuttle)
and it will either slow down air coming out, or stuff air in. Cowl induction works on that principle.
Very nice looking vents though Hellfire, they suit the car well.
Cheers.
[edit] When I say hood, I mean bonnet. Always forget that one . Also I should mention that having your rad fan shrouded so that it is
pulling/pushing air through ALL of the rad and not just a small area is required for optimal cooling in traffic. You would be suprised at how much
that helps.
[Edited on 23/1/06 by C10CoryM]
"Our watchword evermore shall be: The Maple Leaf Forever!"
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Spyderman
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| posted on 24/1/06 at 02:09 PM |
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What a load of ballony gets talked about air pressures and aerodynamics!
First off, no amounts of increasing the underbonnet air pressure will cause lifting of car/bonnet of any sort. It is only the high speed low pressure
air that flows across the top of the bonnet that will cause it to lift. So fit as many vents as you like, it won't change! If you don't
believe me try cellotaping, across front edge, a piece of paper to the table and then blowing across it. The paper will lift even though air can not
get under the front.
Venting the engine bay would best be achieved with vents as near to the radiator as possible and preferably alongside the front wheels. This is due to
this area being a low pressure area where the air travels fastest between wheel and body. Vents across the front of the bonnet area would also be good
for expelling hot air as well, but would most probably interfere with any intake for engine if this is in bonnet.
Vents nearer to the scuttle although effective at low to medium speeds become less effective as the speeds increase due to turbulence, particularly
when a full screen is used. However the opposite may be true for side vents at the rear of the engine bay as airflow increases with increase in speed
so their effectiveness increases.
Sorry about the rant, but it is one of my pet subjects!
Terry
Spyderman
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C10CoryM
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| posted on 24/1/06 at 05:29 PM |
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Well, You will have to explain how it is "ballony" to me. Unless things work different on your side of the pond, lift/downforce comes
from high pressure areas trying to get to the low pressure areas. Far as I know there is nothing you can do about the high speed low pressure area
above the bonnet other than drive slow. Screw that! You can however do something about the the low speed high pressure area under the bonnet which
is why it actually matters and why I talk about it. Correct me if I am wrong, but if you have low pressure on top of the bonnet, and higher
pressure underneath it, the bonnet is going to try to lift. Since the car is attached to the bonnet, it will see some lift as well. Same reason why
you want to reduce the pressure undercar as much as possible so that the high pressure areas on top of the car (front spoiler,cowl, rear spoiler) push
down on the car trying to get into the low pressure area.
"Our watchword evermore shall be: The Maple Leaf Forever!"
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Rob Palin
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| posted on 24/1/06 at 08:38 PM |
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You missed a trick there Spyderman - you could have said that a lot of hot air was talked about aerodynamics. 
What Locost_Bryan and C10CoryM are saying is perfectly true and unfortunately it is you who are mistaken on this occasion.
The lift force which acts on the bonnet is due primarily to the pressure underneath being raised above the ambient static pressure by the air coming
in through the front of the car. The static pressure above the bonnet is not actually much different from that a long way away from any influence of
the car or its movement (though admittedly that above the front half of the nose will be lower).
The explanation offered about how the lift originates strikes me as coming from the common misconception that Bernoulli's relationship between
air speed and pressure means that pressure drops when air is moving fast. The crucial detail that is absent from this statement is how the air got to
be going fast in the first place.
If the air is accelerated by a fan or suchlike then the Static Pressure need not increase but the Dynamic Pressure (related to the momentum of the
air) will increase. The sum of the two - unsurprisingly called the Total Pressure will increase. The misconception i mentioned is that people refer
to the expression with Total Pressure as a constant but they miss out the rest of the accompanying information which explains that this is an extra
criterion which actually describes a special case intended to make the maths simpler in some situations and not a true generalisation.
Bernoulli's full equation is not a simplification of the physics but cut-down versions of it are often presented as being the full thing. The
man himself wouldn't have been impressed with how his work gets misrepresented.
If the air is otherwise still but is forced to accelerate to effectively move out of the way of an approaching obstacle then it can
'borrow' from the static pressure to give itself dynamic pressure i.e movement. This is when the static pressure drops. I realise this
sounds like the air is alive and thinking about what it's doing but the detail of why all this happens isn't really appropriate here (also
i don't understand it fully either!).
The pressure around the top of the nosecone is low because the air is accelerating around the convex surface curvature. When it gets onto the flat
part of the bonnet it slows back down and the dynamic pressure it borrowed gets paid back into static pressure. If the bonnet is long enough and flat
enough then the air returns almost to its undisturbed condition and the static pressure will be near as dammit the same as atmospheric pressure.
Exit louvres are best placed somewhere around the middle of the nosecone or the front of the bonnet. After that you do not get any 'pull'
from the air flowing over those surfaces and you have to rely soley on the 'push' from the high pressure air coming in through the nose
inlet.
Vents near the scuttle will only be effective outlets when the car is stationary or moving very slowly and the air flow is driven by convection or a
cooling fan (when they act as chimneys). Otherwise pressure builds up in front of a concave corner like the bonnet/windscreen join and this will be
the case at both medium and high speeds. It has nothing to do with turbulence, sorry.
Cheers
Rob
(This is a pet subject for me too. And a profession, as it happens.)
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Hellfire
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| posted on 24/1/06 at 11:00 PM |
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The bonnet vents on our Indy do the same job as the bonnet vents on this.
 
Description
OK, slightly different cars aerodynamically I know.......
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chriscook
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| posted on 24/1/06 at 11:10 PM |
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That SLR has vents on the side too, just behind the wheel arches
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Hellfire
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| posted on 24/1/06 at 11:13 PM |
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So does ours, only its not a vent as such. More of a gap.......
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Spyderman
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| posted on 25/1/06 at 12:46 PM |
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I did do a longer reply, but it got lost and I can't be arsed to do it again!
The gist of it was. I am not trying to impress everyone or turn them into experts, just trying to get them to understand some simple concepts in a way
that they might understand without too much research!
Terry
Spyderman
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Rob Palin
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| posted on 25/1/06 at 01:46 PM |
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Hi Terry,
Clearly you had the best intentions but your explanation was incorrect and therefore potentially misleading. All i wanted to do is clarify things a
bit.
What is going on when you blow over a piece of paper held at one end is very different from what's happening over a car bonnet. The paper thing
is explained quite neatly here:
http://www.av8n.com/how/htm/spins.html#sec-coanda
Cheers
Rob
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locost_bryan
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| posted on 25/1/06 at 10:47 PM |
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quote:
Originally posted by Spyderman
What a load of ballony gets talked about air pressures and aerodynamics!
First off, no amounts of increasing the underbonnet air pressure will cause lifting of car/bonnet of any sort. It is only the high speed low pressure
air that flows across the top of the bonnet that will cause it to lift. So fit as many vents as you like, it won't change! If you don't
believe me try cellotaping, across front edge, a piece of paper to the table and then blowing across it. The paper will lift even though air can not
get under the front.
Experiment 2. Get a show box with a lid. Put a hole in the end of the box. Poke the hose from your vacuum cleaner in the hole. Turn the vacuum
cleaner on to blow. Now, where's the lid gone? Blown right off, it has!  (unless you used Dzeuss fasteners )
Bryan Miller
Auckland NZ
Bruce McLaren - "Where's my F1 car?"
John Cooper - "In that rack of tubes, son"
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locost_bryan
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| posted on 25/1/06 at 10:58 PM |
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quote:
Originally posted by chriscook
That SLR has vents on the side too, just behind the wheel arches
it also has a much more laid back windscreen.
just take a look at the reversed bonnet scoops on many 70's and 80's thundersaloons, that took a cold air feed from the base of the
windscreen
Bryan Miller
Auckland NZ
Bruce McLaren - "Where's my F1 car?"
John Cooper - "In that rack of tubes, son"
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Rob Palin
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| posted on 26/1/06 at 07:38 AM |
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Also worth considering that even McLaren's mighty aerodynamics experts may have lost out in a road car development process to the all-powerful
force of the stylist. They rule in F1 but for road cars the stylist is king.
About 50% of my job is fixing problems with cars which have arisen through someone somewhere deciding that it's either prettier or perhaps
cheaper to compromise on the aerodynamics. Even the big names occasionally make such mistakes. Can't complain though - keeps me off the
streets!
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Hellfire
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| posted on 26/1/06 at 12:53 PM |
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quote:
Originally posted by locost_bryan
quote:
Originally posted by Spyderman
What a load of ballony gets talked about air pressures and aerodynamics!
First off, no amounts of increasing the underbonnet air pressure will cause lifting of car/bonnet of any sort. It is only the high speed low pressure
air that flows across the top of the bonnet that will cause it to lift. So fit as many vents as you like, it won't change! If you don't
believe me try cellotaping, across front edge, a piece of paper to the table and then blowing across it. The paper will lift even though air can not
get under the front.
Experiment 2. Get a show box with a lid. Put a hole in the end of the box. Poke the hose from your vacuum cleaner in the hole. Turn the vacuum
cleaner on to blow. Now, where's the lid gone? Blown right off, it has! (unless you used Dzeuss fasteners )
Sorry but I can't see how that has anything to do with aerodynamics and bonnet lift on a seven style car. Maybe if you were to repeat that
experiment but instead, take the bottom out of the box, cut a few small holes in the sides and then a few small holes in the lid and then hold the
vacuum cleaner nozzle a foot or so away from the box, I doubt very much that the lid would blow off.
Phil
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locost_bryan
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| posted on 26/1/06 at 11:58 PM |
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quote:
Originally posted by Hellfire
Sorry but I can't see how that has anything to do with aerodynamics and bonnet lift on a seven style car. Maybe if you were to repeat that
experiment but instead, take the bottom out of the box, cut a few small holes in the sides and then a few small holes in the lid and then hold the
vacuum cleaner nozzle a foot or so away from the box, I doubt very much that the lid would blow off.
Phil
aerodynamics and seven in the same sentence?
If you cut the bottom off the shoe box, then the whole box would lift off the ground (like a hovercraft).
The original post related to vents for removing under-bonnet air.
The problem with the Seven/Locost is that air is forced in through a small opening at the front and is vented out through the bottom of the engine
bay. This creates some lift and a hell of a lot of drag!
That was what Experiment 2 was intended to illustrate (finding a pointy shoebox and a really powerful vacuum cleaner might be a bit of a
challenge!)
Experiment 1 (blowing over a piece of paper) is also somewhat flawed unless you've made an origami Locost
I'm sure someone has the formula for figuring out how big the outlet vents need to be - the size of the nose inlet multiplied by a factor for
the heat absorbed.
No doubt the Locost nose is far from optimum! 
[Edited on 27-1-06 by locost_bryan]
Bryan Miller
Auckland NZ
Bruce McLaren - "Where's my F1 car?"
John Cooper - "In that rack of tubes, son"
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