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Discussion Starter · #1 ·
hey guys...

i've always liked the look of vented bonnets and i've seen a number of dyno results showing more power due to the vented bonnet allowing the hot air to escape. not THAT much more power, but more power none the less,

but my concern is what do people do when it rains!?? lol..

ive always thought it was not good for water to be inside the engine bay due to electrical components, and even the intakes sucking up water...

can anyone elaborate and explain the situation here?
 

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I too have often worried about the wet stuff getting in, if you have a vented bonnet, so i will be watching this thread with iinterest. I no some suppliers do these with rain channels which im sure is fine if the car is stationary, but what about when your doing motorway speeds?
 

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hey guys...

i've always liked the look of vented bonnets and i've seen a number of dyno results showing more power due to the vented bonnet allowing the hot air to escape. not THAT much more power, but more power none the less,

but my concern is what do people do when it rains!?? lol..

ive always thought it was not good for water to be inside the engine bay due to electrical components, and even the intakes sucking up water...

can anyone elaborate and explain the situation here?
Don't do it mate, sure the vents help the engine stay cooler, but you will have a lot of problems occuring due to water seeping in one way or another. Coil pack problems, fan belt, alternator belt, power steering etc problems.
not worth it at all unless you can somehow manage to channel water away from the engine itself. With vents your car will become very impractical when you take it for a wash, or when suddenly it starts raining as it always bloody does in uk. I have had a lot of stress due to the bonnet vents. Cannot leave the car uncovered ever, need to tell the guys at hand car wash place not to spray the bonnet and when Im away from home and it starts raining I simply do not drive. Every time I want to take the car out Im on the BBC website looking for the weather forecast. My missus is annoyed with it and thinks Im going absolutely mad.:runaway:
picture below, the side vents are ok, but the middle vent pain in the back side.

 

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bear in mind that all bonnet vents should be baffled (or have some sort of "tray" arrangement" - here in NZ it's a legal requirement. The reason being: if you are driving along at 60mph etc and your radiator hose blows out, where does all that hot water end up? on your screen! Worse if it's a high-pressure oil line that blows - oil tends to be less transparent.

Anyway, bear that in mind when you stick whopping great holes in your bonnet - it may not just be air coming out :)
 

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i had one on my old mkiv supra and didnt really have a problem tbh, it was just as normal but looked a hel of alot better, i didnt have any trays or such
i dont know how the skyline would react though but i cant imagine it would be much worse

Alex
 

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I bought a cotton wool sheet from B&Q which I put on the engine before I cover up the car, making sure not a drop of water seeps in from rain or from winter condensation of air. If it does the cotton insulation sheet can soak it up. Hardly drive the car, but if I do it takes me at least half an hour in preparation before it is ready to drive. :runaway:
 

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hi guys, i used stickaflex and bonded to L-shaped pieces to the underside of the bonnet, the tray is alloy and has a 10mm lip all the way round, two drain holes on the front left and front right allow water to drip where it affects nothing under the bonnet. once the L-pieces are bonded i slide the tray in and used to small self tappers to hold in place. i can remove it for trackdays and hot weather.bernie
 

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Discussion Starter · #13 ·
I bought a cotton wool sheet from B&Q which I put on the engine before I cover up the car, making sure not a drop of water seeps in from rain or from winter condensation of air. If it does the cotton insulation sheet can soak it up. Hardly drive the car, but if I do it takes me at least half an hour in preparation before it is ready to drive. :runaway:
thats terrible.. i would be really upset if i had to do that everytime i wanted to drive my car, how does that NOT drive you mad?



hi guys, i used stickaflex and bonded to L-shaped pieces to the underside of the bonnet, the tray is alloy and has a 10mm lip all the way round, two drain holes on the front left and front right allow water to drip where it affects nothing under the bonnet. once the L-pieces are bonded i slide the tray in and used to small self tappers to hold in place. i can remove it for trackdays and hot weather.bernie
that seems to me like it could very well counter act the whole point of a vented bonnet in the first place.. a metal sheet would reflect the heat back towards the motor more than anything else.... unless your just at it for looks? then that would be ok.
 

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thats terrible.. i would be really upset if i had to do that everytime i wanted to drive my car, how does that NOT drive you mad?





that seems to me like it could very well counter act the whole point of a vented bonnet in the first place.. a metal sheet would reflect the heat back towards the motor more than anything else.... unless your just at it for looks? then that would be ok.

you would be surprised how much heat the engine and the fan blow out of there..i have it in the boot alot of the time in summer and then put it on at night time just incase it pores down during the night, it takes less than a minute to remove and it can rain all it wants when its on..
 

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Better quality vented bonnets have rain channels built in, they also tend to avoid having vents directly over the engine, as you don't want to get too much water on the top where it'll collect and sit. Look at standard vented bonnets for an idea, (TVR's spring to mind), they usually have vents right at the front, (over the radiator), and along the sides.

Most vented bonnets will be ok though, engine bays are not water tight, so a little extra that gets through a vent will make no difference.

Alex B
 

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Take the rubber strip off the top of the rear bulkhead as that seals against the bonnet. Then either stick three or four washers, or make four small hollow posts, and stick those between the bonnet and the hinge and bolt through. That lifts the bonnet up near the windscreen to create a gap, allowing air to vent from the engine bay out the back/top.

But only when driving along, not when on dyno. When on the dyno just leave the bonnet open........

Biggest trouble with aftermarket bonnets, unless they are really good (i.e. expensive) is that they are mechanically quite weak and will 'bow' with all the air pressure when driving at speed. This can become a major issue if it pulls hard enough on the front catch that it breaks loose and the bonnet flies up.

Most inconvenient, especially if it then breaks the windscreen.
 

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PO of my car had a Nismo copy on, water had definitely sat on the engine as a result - the paint was knackered on the centre and cam covers. Not a good idea for a bling engine bay it seems.
 

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PO of my car had a Nismo copy on, water had definitely sat on the engine as a result - the paint was knackered on the centre and cam covers. Not a good idea for a bling engine bay it seems.
I had a genuine Nismo on my R34 GT-R daily driver, wind,rain & snow, no issues whatsoever, except the price:runaway:

Dave.
 

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Take the rubber strip off the top of the rear bulkhead as that seals against the bonnet. Then either stick three or four washers, or make four small hollow posts, and stick those between the bonnet and the hinge and bolt through. That lifts the bonnet up near the windscreen to create a gap, allowing air to vent from the engine bay out the back/top.
Sorry, but anyone who knows much about car aerodynamics will disagree with this. Lifting the back of the bonnet up makes air enter the underbonnet from the back (at road speeds).

There is a much higher pressure at the base of the windscreen than there is inside the engine bay, so this mod is not a good idea for additional venting, and the additional under bonnet pressure that you would get doing this mod will make a popped bonnet more likely while driving.

I doubt many aftermarket bonnets have been designed in a wind tunnel, and suspect many of them do not give additional venting to the engine bay, at anything other than zero or very low road speeds. So a rain undertray is hardly likely to upset the critical aero package incorporated in your average AM vented bonnet.
 
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