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bonnet vents ( air intake) 

 

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 Post subject: bonnet vents ( air intake)
Posted: Tue Aug 05, 2008 8:03 pm 
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how can i stop water ( on rainy days)...or water in general from getting on my engine and watever else under the hood with bonnet vents.

im looking at putting these on my bonnet and putting mesh over them to stop big s**t going in (DUH!).

is their anyway 2 stop water...any1 else put vents in their bonnet and notice a difference in performance but more importantly engine temperature?

thanks
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Posted: Wed Aug 06, 2008 12:06 am 
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unless you put the vents right up the front of the bonnet, they will be in high pressure areas, meaning nothing comes out, but everything gets sucked in.

Put them about 4 inches from the front edge of the bonnet (give or take) and it will be in a low pressure area and the pressure of air under the bonnet will be higher than the pressure above and air will go out the bonnet vents.. obviously cars differ, but that is the general rule.
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Posted: Wed Aug 06, 2008 8:59 am 
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you're not referring to the stock vents that came with the EF/L xr6/8's are you?

If you are (by chance) they are closed off and don't let anything thru so there is no hassle.

 

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Posted: Wed Aug 06, 2008 11:45 am 
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^^Yes they do they fill up with water then drain it into the bonnet lining which in time completely screws the thing up.

 

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Posted: Wed Aug 06, 2008 6:50 pm 
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no i just bought a bonnet with a BA bulge on it and it has 2 bonnet vents on the top part of the bonnet. air intake is the purpose of them.

what i was thinking was below...did it in 1min !!!

the bulge is sitting on the bonnet with a whole in the bonnet ( bulge sitting over the top of it). i was thinking of filling up that hole in the bonnet with a bit of fibreglass or watever and leave maybe 1/4 of the panel out so it looks like the picture below.

this would eliminate water getting into the engine because it would evaporate before it got into the bay...hopefully.

but questions are would this reduce the point of the vents?

another idea was getting 2 lengths of flexible hose and taking them from the vents and then to somewhere in the engine bay or both to the airbox??

thoughts?

 

 

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Posted: Wed Aug 06, 2008 6:58 pm 
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Autospeed does a good write up on this..

They tested cars.. and found that the back 2/3's of the bonnet has pressure higher than under the hood.. the front has low pressure.

You can draw air in though your radiator/intercooler etc to improve cooling by creating a lower pressure in the engine bay.. easiest way to do that, is by putting bonnet vents in where there is a lower pressure outside than the pressure inside.. and that means in the first 1.5 foot of the front edge of the bonnet.

The back of the bonnet is high pressure, that is why it's the intake for the fan etc.. because air gets forced in.
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Posted: Wed Aug 06, 2008 7:20 pm 
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Alot of performance cars etc and fibresports have their vents at the back of the bonnet. IMO air would come in the front and vent out the back??
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Posted: Wed Aug 06, 2008 7:33 pm 
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No...

Air hits the widescreen and creates a high pressure area as it builds up and flows over the car..

That high pressure area extends for a fair way in front of the back edge of the bonnet.

Have a read of the autospeed article.. they actually put pressure sensors all over the front of a car and took it for hoons to find the best place for vents.. they are not guessing.

Last edited by frankieh on Wed Aug 06, 2008 8:32 pm, edited 1 time in total.

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Posted: Wed Aug 06, 2008 7:54 pm 
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ok all that HP LP stuff just went over my head...

so is my setup good or not good?
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Posted: Wed Aug 06, 2008 8:19 pm 
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not really no...

it looks like you want air to flow out of that vent. but its in a high pressure area, so the only way to get it to flow air out efficiently is to increase the air pressure under the bonnet to higher than above it.. the problem with that is that your radiator will then massively under perform.
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Posted: Wed Aug 06, 2008 9:09 pm 
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well air in or air out.

the air outside is always going to be cooler than the air inside. so if it sucks the air in from the outside it isnt a bad thing etha
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Posted: Wed Aug 06, 2008 9:25 pm 
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yes, but you want flow though...

in at the bottom though radiator etc.. and out at the top..

That way will flow allot more and everything gets cooler.

they do a heap of study of this on autospeed.com

go have a read.. its quite interesting.
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Posted: Wed Aug 06, 2008 9:51 pm 
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hence why the cosworth vents are at the front.

engineers spent money on r&d to put them there.

 

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Posted: Wed Aug 06, 2008 11:31 pm 
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Yup... here is one from the inside.


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Posted: Thu Aug 07, 2008 12:44 am 
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so then do you guys think a vent in your bonnet between your radiator and engine would be beneficial?
heat soaked air from radiator straight outta the bonnet,
without afecting the other heat dynamics of the car to much
ive heard your engine performs better when your headers are hot.
{i once had the stoopid idea of a small thermo fan mounted above the headers}
i spose you could heat wrap them,looks shight but
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