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Location:
Lismore, NSW
Registered:
February 2003
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Cooling on well any car!!!
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Sat, 11 December 2004 05:39
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Does raising the bonnet at the back by using washers on the bonnet hinges help to decrease underbonnet heat? Basically I want to cool down my airtemp a little more going into the motor
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Location:
Brisbane
Registered:
May 2004
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Re: Cooling on well any car!!!
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Sat, 11 December 2004 07:01
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It reduces the ambient heat around inlet components by venting hot air from around the exhaust side of the engine.
Mind you, I am pretty sure it is illegal as the raised bonnet would act as a giant blade aimed at your neck in a crash.
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Location:
Noosa
Registered:
November 2004
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Re: Cooling on well any car!!!
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Sat, 11 December 2004 07:06
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Call me an idiot but what i've done is ripped the rubber thing off at the back of the bonnet and taken the plastic panning off the car (you know the stuff. Also the 'rolla has a fan sensor on the water/radiator hose which was unplugged so the fans on all the time.
Hope this helps. 
Cheers
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Location:
Lismore, NSW
Registered:
February 2003
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Re: Cooling on well any car!!!
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Sun, 12 December 2004 01:12
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Didn't think about the rubber sealing the bonnet to the plenum, I might just remove that and see if I notice any difference in airtemps etc. I will just have to make sure no water gets into my spark plug wells. Cheers
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Registered:
May 2004
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Re: Cooling on well any car!!!
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Sun, 12 December 2004 01:29
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| Quote: |
Call me an idiot but what i've done is ripped the rubber thing off at the back of the bonnet and taken the plastic panning off the car (you know the stuff. Also the 'rolla has a fan sensor on the water/radiator hose which was unplugged so the fans on all the time.
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Idiot.
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Location:
On your mum!
Registered:
May 2002
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Re: Cooling on well any car!!!
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Sun, 12 December 2004 06:39
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| colouring_in_book wrote on Sun, 12 December 2004 12:29 |
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Call me an idiot but what i've done is ripped the rubber thing off at the back of the bonnet and taken the plastic panning off the car (you know the stuff. Also the 'rolla has a fan sensor on the water/radiator hose which was unplugged so the fans on all the time.
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Idiot.
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Hahaha
The plastic piece at the bottom actually helps the engie stay cool while idling in traffic etc by kerbing the recirculation of hot air from the engine bay back though the radiator.
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I supported Toymods
Location:
Epping, Sydney
Registered:
May 2002
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Re: Cooling on well any car!!!
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Sun, 12 December 2004 07:57
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you can also remove the rubber strip at the back of most bonnets, nearest the windscreen. not sure on the legality of this
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Location:
Castle Hill, Sydney
Registered:
February 2004
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Re: Cooling on well any car!!!
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Sun, 12 December 2004 08:17
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yeah its great fun when u start leaking oil/water and it sprays all over your windscreen and you crash into a pole and die
i've heard about the hole cutting off your head thing, i dont see why it would be any more likely doing that than to a normal bonnet, its still mounted the same way, just make sure longer bolts are used.
and i thought one of the main reasons for this was also better aerodynamics get some nice airflow coming thorugh the engine and over the roof
illegal!
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I supported Toymods
Location:
Epping, Sydney
Registered:
May 2002
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Re: Cooling on well any car!!!
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Sun, 12 December 2004 08:42
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well
I'm gonna go out on a limb here and suggest that if you start leaking oil and water enough that it starts to coat your windscreen, a sensible person would pull over before their vision becomes blocked and their engine becomes FUBAR. that said, a sensible person would probably go to a bodywork place and pay $500 to get a couple of cheap vents put in their bonnet
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Location:
Brisbane
Registered:
February 2003
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Location:
Montrose, VIC
Registered:
May 2002
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Re: Cooling on well any car!!!
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Mon, 13 December 2004 01:11
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As for letting your fan run all the time, think of it this way - does YOUR fan make an 80+km/h breeze through the radiator?
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Location:
Sydney
Registered:
May 2004
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Re: Cooling on well any car!!!
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Mon, 13 December 2004 03:03
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Toyota would have done a lot of testing on your car to make sure it wouldn't over heat. They'd probably leave it out in the dessert or something but just remember that you car runs rich when cold. It's true that colder air intake = power but if it's at the cost of your engine never warming up to it's normal temp think again!
If the purpose of you raising the bonnet is to make the air intake temp cooler why don't you just make a cold air intake? Or if it's just a rice thing save the time/money for a bigger rear spoiler
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Location:
Melbourne
Registered:
May 2002
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Re: Cooling on well any car!!!
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Mon, 13 December 2004 04:27
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The rear edge of a bonnet is a high pressure area whilst moving, so rather than venting air out there, it will actually be pushed into the engine bay. Now what you've done is disrupted the air flow that toyota took time to design. Your engine will run hotter because less air is being forced through the radiator, it will go i through under the windscreen and straight through the bottom.
And if you raise your bonnet high enough off the safey hooks it'll go straight through the windscreen in the event of a crash.
A true cold air intake isn't that hard to make, do it proper and reap the benefits during stop light drags!!!
dodgydan
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Location:
Madrid - Spain
Registered:
August 2002
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Re: Cooling on well any car!!!
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Mon, 13 December 2004 23:26
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| c2888 wrote on Mon, 13 December 2004 15:27 |
The rear edge of a bonnet is a high pressure area whilst moving, so rather than venting air out there, it will actually be pushed into the engine bay.
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Are you sure about this??
The windscreen will see a high pressure due to the dynamic pressure acting normal to the screen, but I am not so sure that the bonnet will be.
The bonnet acts like a wing, creating lift, ie low pressure on top. Now this will reduce at the back of the bonnet but I think you will find that it will still be seeing a low pressure there. Unless of course there is an even lower pressure under the bonnet, which is unlikely.
It should be easy enough to check on a celica/supra. Take it for a drive with teh latch undone. If the back of the bonnet rises, then it is a low pressure. If it pushes down then it is a high pressure.
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Re: Cooling on well any car!!!
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Mon, 13 December 2004 23:55
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| gold28 wrote on Tue, 14 December 2004 10:26 |
| c2888 wrote on Mon, 13 December 2004 15:27 |
The rear edge of a bonnet is a high pressure area whilst moving, so rather than venting air out there, it will actually be pushed into the engine bay.
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Are you sure about this??
The windscreen will see a high pressure due to the dynamic pressure acting normal to the screen, but I am not so sure that the bonnet will be.
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i'm fairly sure this is true. remember that a lot of the air originally in front of the car has gone up and over the bonnet already. if you had a splitter, this would be even more pronounced...
while the air at the bonnet/windscreen might be lower pressure than the radiator air intake point, it will certainly be higher than underneath the car, so you will introduce air into the engine bay...
remember the walkinshaw commonwhores? rear facing air intake? they didn't do this to decrease the intake air pressure 
i also vaguely remember tests that someone did, (maybe J.Edgar) but i can't remember...
all you need to test is to put one end of a crude manometer vertical tube with liquid in it) to the gap at the bonnet, and compare to under car and in front of car.. be careful with the direction of the tube opening as that will affect the pressure readings..
Cya, Stewart
EDIT: and you would be better off having a lower front apron/spliter that directed air around and over the car, to reduce the below engine presure and suck more air thru the radiator and from the rest of the engine bay.
[Updated on: Mon, 13 December 2004 23:56]
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Location:
Madrid - Spain
Registered:
August 2002
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Re: Cooling on well any car!!!
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Tue, 14 December 2004 02:05
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but if this air had come from below the bonnet line, then it would have been accelerated over the bonnet. Thus according to Bernoulli's theorem, the pressure will decrease.
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Re: Cooling on well any car!!!
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Tue, 14 December 2004 03:25
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i guess technically that is correct, over the front section of the bonnet there may be lower pressure, but the rear of the bonnet will be higher than this..
it's hard to find many good pics to illustrate this but
and the animation at..
http://www2.icfd.co.jp/examples/car_p/car2.html
the green area at the back of the bonnet, base of windscreen is green = higher pressure..
http://www.autospeed.com/cms/search/index.html?sco pe=&keywords=aero+testing
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Pressure on top of the bonnet? Why would there be any? The pressure on the surface of the bodywork depends on the aerodynamic flows over it. This DaimlerChrysler graphic shows the typical frontal pressure distribution of a car. Looking just at the bonnet you can see that there is low pressure (blue) where the air wraps around the leading edge of the bonnet, grading to high pressure (green) as the air reaches the obstruction which is the windscreen.
So you wouldn’t site a bonnet outlet vent close to the windscreen – in fact that’s usually where the cabin ventilation inlet ducts are... they’re taking advantage of that high pressure! Looking at just the exterior pressures, what we want at the vent location is the very lowest external pressure.
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http://www.autospeed.com/cms/A_2162/article.html
this help?
Cya, Stewart
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Location:
Brisbane
Registered:
May 2002
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Re: Cooling on well any car!!!
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Tue, 14 December 2004 11:55
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FWIW I did this on my MA61 after I installed the 2JZ and had some cooling issues. I found it did make a noticeable difference, nothing huge but it's something for nothing. The effectiveness of this mod would probably vary from car to car though.
Oh and what thechuckster said is quite correct, you get hot engine bay air and fumes coming into the cabin (eg oil smell every time the BOV vented  ) which is kind of a pain. I haven't raised the bonnet on my new MA61 for this reason, instead I'm looking for a more sophisticated solution to my problem.
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I supported Toymods
Location:
Frankston, Victoria
Registered:
April 2004
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Re: Cooling on well any car!!!
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Tue, 14 December 2004 12:41
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hahahah $500 for bonnet vents  . OK, go down to your local autobarn, buy some vents for like $30 each, get out your trusty angle grinder, chop some holes, epoxy the vents in place, and there you have it, problem solved without breaking any laws (i dont think  ).
Kev.
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Location:
Madrid - Spain
Registered:
August 2002
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Re: Cooling on well any car!!!
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Tue, 14 December 2004 21:11
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Well I guess a picture tells a thousand words.
I was expecting the low pressure area over the bonnet to streatch further back, more like that of the roof shown on the Merc pic. But obviously the high pressure in front of the windscreen is releaving the low pressure from the bonnet. Makes sense really, thats what happens with Aircraft control surfaces.
It is interesting that the nascar pic shows a low pressure at the back of the bonnet. This is probably due to the windscreen not being modeled.
Thanks for the pics Stewart.
Comparing the Merc pic with an early celica. The plenum having a reasonable size would place the end of the bonnet almost in the blue, nominal pressure area of the merc pic. This would mean that there would be little if any pressure differential at the end of the bonnet.
I think I might try some wind tunnel testing on gold28 and see what happens.
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Location:
Campbelltown
Registered:
November 2003
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Re: Cooling on well any car!!!
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Tue, 14 December 2004 22:40
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many ppl that put frount mounts in wrx's then turn the bonnet vent around to vent hot air out of the bay something like this could be done
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Location:
Lismore, NSW
Registered:
February 2003
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Re: Cooling on well any car!!!
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Sun, 19 December 2004 10:41
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My main concern that im trying to resolve is that under boost my inlet temp drops to about 35C even on the hottest days which I think is quite good, but cruising when there's not much velocity in the piping the air heats up to about 45 and idling at maccas dive thru etc it can reach about 55C. How can I reduce these cruising and idling temps? I already have the cold air box + intercooler. Is there a economical way to do this?
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Location:
Sydney
Registered:
July 2002
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Re: Cooling on well any car!!!
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Sun, 19 December 2004 23:31
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This is a cool thread.
Whats the air pressure at the back of the engine bay?? Is it high or low?
If its very high (purple on that first pic) then it will force the hot air through the light blue section wouldn't it?
I wanna put some TA23 vents or something similar on the Supra.
Oh, and I've taken the rubber off the back of my bonnet. I *think* it helped my overheating problems I used to have.
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Location:
Sydney
Registered:
July 2002
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Re: Cooling on well any car!!!
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Sun, 19 December 2004 23:34
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| Celica_John wrote on Mon, 13 December 2004 14:03 |
Toyota would have done a lot of testing on your car to make sure it wouldn't over heat.
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Had to comment on this.
Toyota never designed the engine bays (and cooling systems) to house most of the engines WE have in them.
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Location:
sunny coast, qld
Registered:
October 2002
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Re: Cooling on well any car!!!
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Mon, 20 December 2004 00:05
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hmm, I was planning on having a bonnet scoop to suck the air straight into the air filter on the turbo and then after the turbo put a vent in so that some of the hot air from the exhaust side can get out. So if I put the vent too close to the windscreen it won't actually do anything except suck air back into engine bay.
Does anyone know how the rear of bonnet pressure would be affected with a squarer front end like that of a Corona Does the high pressure area increase at the back depending on the angle of the windscreen?
thanks
Chris
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Location:
Sydney
Registered:
May 2004
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Re: Cooling on well any car!!!
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Tue, 21 December 2004 02:56
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have you thought of an intercooler spray.
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Location:
Sydney
Registered:
May 2004
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Re: Cooling on well any car!!!
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Tue, 21 December 2004 02:57
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| SupraPete wrote on Mon, 20 December 2004 10:34 |
| Celica_John wrote on Mon, 13 December 2004 14:03 |
Toyota would have done a lot of testing on your car to make sure it wouldn't over heat.
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Had to comment on this.
Toyota never designed the engine bays (and cooling systems) to house most of the engines WE have in them.
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Sorry I didn't think we were talking about a car with a different engine.
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