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  1. #1
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    Default Bonnet venting.

    Just wondering if anyone has ever vented a bonnet to expel/extract heat.

    If so, how effective was it?

    Were the vents used more of an 'add on' nature or were they the primary air extraction (instead of under the car)

    I have seen people lift the back of the bonnet, but I think that would probably release air on the sides rather than the back, as the rear of the bonnet is usually in a high pressure area at the base of the screen and the aero would probably be screwed over in the process.

    I don't really like vents and crap in the bonnet, but I'm happy for form to follow function if required.

    I'd prefer something a little more subtle and less ricey than the vent below if possible, but aerodynamically it is actually quite soundly designed.

    The goal is to give the primary airflow through the radiator an easy evacuation route and to reduce high pressure under the car.

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    Fellow Frogger! DjB8V's Avatar
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    I've had this thought on my mind too. Instead of vent air out would it be better too get cooler air into the engine bay and move some of the air round. But I guess the hot air still needs to go somewhere....

    Tricky. Maybe more effort should be put into keeping the engine cooler in the first place thus reducing almost all under bonnet temps.

    Maybe run without a bonnet .....

    Chris

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    Quote Originally Posted by DjB8V View Post
    I've had this thought on my mind too. Instead of vent air out would it be better too get cooler air into the engine bay and move some of the air round. But I guess the hot air still needs to go somewhere....

    Tricky. Maybe more effort should be put into keeping the engine cooler in the first place thus reducing almost all under bonnet temps.

    Maybe run without a bonnet .....

    Chris
    Not sure removing the bonnet would be a good move

    Something like this might work and not require grafting to the bonnet, but I'm not sure if the volume of the vents will be enough...


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    As a pedant for clean glass, I always wonder how much of that dusty oily crap that would normally end up stuck to the underside of the bonnet would end up on the windscreen, (especily in a mitsubishi).

    Jo

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    Default The "new" Fuego ???

    The dual vents do look reasonable set up like that and may look o.k. with the standard Fuego bonnet (I take it that is the car under discussion. I wonder if they would spew anything from the engine and battery compartment onto the windscreen.

    I have a (needs a repaint) replacement Fuego bonnet with the centre bulge if you want to practice modifying that,

    Or why not go the whole ricey hog and put in an "exit pipe on the passenger side, that will draw up under the bonnet and over the engine and expel just above the roof line, using an exhaust fan fitting to boost the flow of air, another more discreet exit would be to each side. I have a few scrappers if you want to test exit points etc.

    Ken

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    An air dam under the radiator will create a low pressure area behind it and suck air out of the engine bay (have a look under current cars like a Commode to see what i mean).

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    IMO...you dont necessarily need a "physical" vent on the bonnet...My suggestion is to build a narrow but wide scoop "inside" engine bay...towards fire wall...and then pipe this to the underside...think of it as the complete opposite of "air induction" systems like the SS...Only thing you have to worry about is that the "inner" scoop sits as close to back of bonnet...let natuaral laws of physics handle the rest ie hot air raises and low pressure spot under car will vent...Consider also fixing the scoop upside down to the bonnet underside and if the 'seal' is completed at point of bonnet pivot, seal to pipe (fixed to firewall) should be good and effective... good luck




    dino

    ps...should you consider usingt he bonnet underside as a support for tge "upside down scoop" make sure you heat shield bonnet so you dont end up with silly things like paint blistering...

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    After putting the V6 turbo engine into my 504, I ended up getting 4 lines of vents put into my 504 bonnet. I think these work really well, and you can see the heat eminating out from them when you stop.

    In my opinion they work very well and are well worth doing - it cost me $130 for the louvres to be pressed into the car.

    I don't have a picture handy unfortunately.

    Regards,
    Andrew

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    Quote Originally Posted by 2CV David View Post
    An air dam under the radiator will create a low pressure area behind it and suck air out of the engine bay (have a look under current cars like a Commode to see what i mean).
    That is how the design works (well supposed to work) from the factory and is what I am trying to avoid/minimise.

    I want to keep (and enhance) that low pressure area under the car so I don't want to fill it with hot expanding air or atleast reduce the amount of infill.

    Dino, your idea is not without technical merit, but requires the car have sufficient airspeed to create a useful venturi. I don't think underbonnet teperatures are a big problem at speed anyway, it's when you are at low speed or stopped that heat soak really takes hold.

    It would also fill the low pressure area under the car which is a negative.

    Roo504, louvres were my original choice, but I have had trouble finding someone who can actually do the bloody things on a bonnet.

    Can you remember who you got to do yours?

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    Real cars have hydraulics DoubleChevron's Avatar
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    Before you go wasting time and even possibly making your car run hotter, have a read of this brilliant article !!!

    http://autospeed.com.au/A_2159/cms/article.html

    seeya,
    Shane L.
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    Quote Originally Posted by mistareno View Post
    That is how the design works (well supposed to work) from the factory and is what I am trying to avoid/minimise.

    I want to keep (and enhance) that low pressure area under the car so I don't want to fill it with hot expanding air or atleast reduce the amount of infill.

    Dino, your idea is not without technical merit, but requires the car have sufficient airspeed to create a useful venturi. I don't think underbonnet teperatures are a big problem at speed anyway, it's when you are at low speed or stopped that heat soak really takes hold.

    It would also fill the low pressure area under the car which is a negative.

    Roo504, louvres were my original choice, but I have had trouble finding someone who can actually do the bloody things on a bonnet.

    Can you remember who you got to do yours?
    Batman automotive college had such a machine to do high quality vents, and as a former tradie you might be able to access a re-training course there in the dark arts of panel beating, spraying etc and get access to the machinery in the process.

    I went to enrol in a hobby course there years ago and instead they enrolled me in a post apprentice course so i could make my life useful after retirement or whatever!!

    Those of italian/european heritage used to just about wet themselves when using the louvering machine, to the extent they put vents everywhere in their projects it was so easy!!

    Ken

    Ken

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    After doing the 205 turbo 400hp conversion way back back in 2007 we realised it got mighty hot under there and then did alot of homework on how to eradicate most of the heat.
    After much homework we came up with these 2 . They worked a treat.

    1. raising the rear of the bonnet by just a few cm's dropped the temps by a tested 10 degrees C.

    2. Placing Lotus 7 style vents in to the bonnet [$300 ] made things even cooler. Streamers were placed on the vents and it was shown that they worked really well however make sure the vents are facing the correct way. It was found that placing them 70% up the bonnet from the front had the most effect.
    jr20516v

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    Previous: Honda EP3 Supercharged , 205 x34 [ including MI16 TURBO, 8v TURBO, CTI, 16V+TB's, 8V+TB's,] Fiat X1-9 X3, Beta coupes x5, Lancia Gamma coupe, GTI-R, Corvette C4, Fiero x5, Alpine GTA turbo, r5 GTT Dimma, 2cv ripple nose, Lotus Elise, 205 Dimma TT, Cliosport 172.x2, Clio rs 200

  13. #13
    bob
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    G'day,

    standard fug bonnet bounces a bit in traffic with cross winds and tends to put the wind up you if you have ever had a catch fail.... :-)

    Will vents reduce that by allowing the air out or is there that much volume of air involved that they will not exhaust it effectively ? In which case bonnet may be weakened enough by the holes to allow even more flexing....

    cheers,
    Bob

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    Have you thought about vents in the inner guards? This takes the heat away from the lower part of the engine where it causes most problems and the extraction should not impinge upon the underbody aeros.
    FLASH

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    Quote Originally Posted by DoubleChevron View Post
    Before you go wasting time and even possibly making your car run hotter, have a read of this brilliant article !!!

    http://autospeed.com.au/A_2159/cms/article.html

    seeya,
    Shane L.
    Not sure what you're getting at.

    Yes, I've read it before and I am actually doing exactly what the article says -

    With extra exit vents in the bonnet preventing any build-up in engine bay pressure, best flow through the radiator is gained. (Of course, you can substitute ‘intercooler’ or ‘oil cooler’ for radiator, if in fact their exit flows are also into the engine bay.)

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    Quote Originally Posted by bob View Post
    In which case bonnet may be weakened enough by the holes to allow even more flexing....
    I think as long as none of the reinforcements are cut, it should be the same. The '3D' nature of a large vent grafted into the bonnet (as opposed to sheet metal) may actually strengthen it slightly.

    I imagine louvres would weaken it a little, but again, aslong as none of the structure is cut, it should be negligible.

  17. #17
    Real cars have hydraulics DoubleChevron's Avatar
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    Quote Originally Posted by mistareno View Post
    Not sure what you're getting at.

    Yes, I've read it before and I am actually doing exactly what the article says -
    Did I link the wrong article ?? The was an article on high and low pressure zones. If you put a bonnet vent int he wrong spot, you can make the car run far hotter. You see there is only so much air that can "exit" the under bonnet area. If you vent ends up in a high pressure spot, it'll push air under the bonnet (rather than vent air), this extra air now needs to escape the underbonnet area so can reduce the amount of air flow through the radiator. If it's an intake for an intercooler for example and it ends up in a low pressure area, the area will slowly flow out of the vent rather than be forced through the intercooler under pressure. So the intercooler will get barely any airflow at all.

    seeya,
    Shane L.
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  18. #18
    I might be slow... DRTDVL's Avatar
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    This company make some amazing products: http://exa.com/

    If you want to get uber-geeky about it - get their software called powerflow.

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    I lifted the rear of the bonnet by about 30mm and removed the rubber strip that seals the underside of the bonnet with the firewall (it's only plastic clips holding it on).

    The thermo fans only work half as much now and as JR said, easily dropped temps by 10 deg

    ..and the bonus was I didn't have to buy any corny wrx or evo style vent to stuff up my humpy bonnet!
    ....now watch a Peugeot turn into a corner!

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    Quote Originally Posted by PugMonkey View Post
    I lifted the rear of the bonnet by about 30mm and removed the rubber strip that seals the underside of the bonnet with the firewall (it's only plastic clips holding it on).

    The thermo fans only work half as much now and as JR said, easily dropped temps by 10 deg

    ..and the bonus was I didn't have to buy any corny wrx or evo style vent to stuff up my humpy bonnet!
    Unfortunately I can't lift the back of the bonnet on a Fuego as the bonnet doubles as the lid for the ventilation plenum chamber.

    If I lift the bonnet up, air from the engine bay can get straight into the ventilation system.

  21. #21
    1000+ Posts jo proffi's Avatar
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    Quote Originally Posted by mistareno View Post
    Unfortunately I can't lift the back of the bonnet on a Fuego as the bonnet doubles as the lid for the ventilation plenum chamber.

    If I lift the bonnet up, air from the engine bay can get straight into the ventilation system.
    Not to mention how crap it looks when the bonnet line doesn't run parallel with the plastic trim.

    Jo

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    Quote Originally Posted by DoubleChevron View Post
    Did I link the wrong article ?? The was an article on high and low pressure zones. If you put a bonnet vent int he wrong spot, you can make the car run far hotter. You see there is only so much air that can "exit" the under bonnet area. If you vent ends up in a high pressure spot, it'll push air under the bonnet (rather than vent air), this extra air now needs to escape the underbonnet area so can reduce the amount of air flow through the radiator. If it's an intake for an intercooler for example and it ends up in a low pressure area, the area will slowly flow out of the vent rather than be forced through the intercooler under pressure. So the intercooler will get barely any airflow at all.

    seeya,
    Shane L.
    I think it was the right article, just the wrong topic.

    The common terminology is that a scoop/duct gets air in and a vent gets it out.

    The article starts with bonnet vents (which is all applicable to what I am doing) and at the end had a bit on scoops also (the opposite to a vent - I think they refer to it as an intake vent which confuses things somewhat).

    They tested a bonnet mounted scoop that fed air to an intercooler but at speed there was no pressure differential across the scoop (and no airflowdue to the build up of air under the bonnet.

    The common consensus seems to be that a vent anywhere in the middle two quarters of the bonnet will work well.

    The only way a bonnet vent won't work is if you put it at the front leading edge (high pressure area) or at the rear where it meets the windscreen (high pressure area)

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    Isn't that what we all strive for? ...the smell of unburnt fuel, the stench of moist oil cooking on the headers and the flakes of hot rubber through our hair!
    ....now watch a Peugeot turn into a corner!

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    Quote Originally Posted by PugMonkey View Post
    Isn't that what we all strive for? ...the smell of unburnt fuel, the stench of moist oil cooking on the headers and the flakes of hot rubber through our hair!
    Not married then I take it?

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    I think I might just keep it simple and fit a pair of these:




    or these:



    They are both the same size although the vent area of the open one might be a little higher but the flow would be impeded by the mesh and it's too big to leave open.

    Probably fit them halfway up the bonnet like this 968 or whatever it is:


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