Vented hoods....Do they work?

Do these actually work? Logical thinking would indicate warm air rises and passes through the vents but what difference do they make to engine bay temps, has there ever been tests done e.t.c?

Reason I ask, I'm really liking the oem hood and would like to source a fibreglass one or a CF one(I know seibon do them), it would be painted anyway, but as I'm almost single would this be a bad move, I dont want to increase the chances of det just for a look, but if it dont make that much of a difference then I'll be changing

I have a shiftsports FRP bonnet just now, and I do love it, the build quality is fantastic for an FRP bonnet and has never let me down, but I reeeeally fancy an FRP oem style bonnet

I have a vented bonnet on my TT and the amount of heat thats released is unreal. When you pull up at lights you cans see the heat rising from the vent. This cant be a bad thing as a Supra engine does get really hot.

I agree but surely the other areas of the hood aren't as hard pressed in terms of pressure so there would be somewhere else for the warm air to vent to, albeit it may take the air that bit longer

Some interesting posts on vent design here:

http://www.eng-tips.com/viewthread.cfm?qid=61524&page=10

I've got a chargespeed bonnet and you defo see alot of heat coming out when sitting at lights etc.

I've got a chargespeed bonnet and you defo see alot of heat coming out when sitting at lights etc.

i dont think anyone would dispute this at standstill, the problem comes at speed when no one can see the heat haze, i did plan on sticking a thermocouple under my stock bonnet before i went vented but forgot !, at speed it would not surprise me to find a vented bonnet is less effecient than a stock bonnet, anyone taken any temperature readings to disproove this ?

I remember reading something a few years back about the stock bonnet was the best option,because the temprature under the bonnet helped with atomising the fuel spray pattern in the fuel injectors.This was designed from Toyota,so it must be right

anyone with experience with rx7 s will know they do make a big difference.

With supras, hmmm not so sure as I am not aware that engine temperatures at a standstill get so hot that it significantly inhibit performance.

That said, lower temperatures are always good for an engine, particularly for a turbo charged car. By that logic they can only be good.

Didn't know about the spray pattern. Good info cheers.

Do Luck have a bonnet which drags hot air from many places under the bonnet. I think it works on a venturi effect. They are £500 though.

...This was designed from Toyota,so it must be right

So was the original TRD bonnet

I'm toying with one of those for trackday usage, but I'll probably stick with stock for daily use.

Do Luck have a bonnet which drags hot air from many places under the bonnet. I think it works on a venturi effect. They are £500 though.

Isn't 500quid for a bonnet the norm?

And if you have a read at that article included(thanks for that;)) you will know that the intake on the Do Luck Bonnet is an intake only, it doesn't vent any warm air anywhere, i.e. there is nowhere to drag it to, so again pretty pointless even as an intake as it is nowhere near our intake pipes

Isn't 500quid for a bonnet the norm?

 

And if you have a read at that article included(thanks for that;)) you will know that the intake on the Do Luck Bonnet is an intake only, it doesn't vent any warm air anywhere, i.e. there is nowhere to drag it to, so again pretty pointless even as an intake as it is nowhere near our intake pipes

Actually, the do-luck bonnet does vent it out the back near the windscreen. See attached pic from Japanese website. It's not on the UK website for some weird reason.

Translated means:

Lift Up Bonnet

ラジエターの熱を後方に抜くための形状。 Radiator to heat back out of shape

i had a vented hood once, it was miles better than getting all that wind resistance when going fast:blink: on my bmx when i was 12:p

The border racing bonnet has 2 stips that channel hot air out (apparently) however it is not cheap think its around the £700 mark

i dont think anyone would dispute this at standstill, the problem comes at speed when no one can see the heat haze, i did plan on sticking a thermocouple under my stock bonnet before i went vented but forgot !, at speed it would not surprise me to find a vented bonnet is less effecient than a stock bonnet, anyone taken any temperature readings to disproove this ?

Surely air moving along the top of the vent only aids the efficiency. As more cool air passes it allows more of the heat to be transfered to the cool air as its moving and thefefore constantly cool as opposed to the air above the bonnet warming up and staying warm at a stand still.

Like a fan in a sunbead moving air is far better than it standing there not moving collecting the heat and not moving it on

Does that make the under bonnet temps anycooler tho?

What problems would warm air thats risen to the top of the engine bay be causing to an engine in the first place(apart from peeling the paint from the bonnet),

I'm going to be quite sceptic here because I've been fooled with after market bollox before,

I can see where an air intake from the front bumper would drag(or rather push) warm air up and out, which may make a difference(at least to ambient air temps in the bay) but to flow over it wouldnt make much difference I'd imagine

Surely air moving along the top of the vent only aids the efficiency. As more cool air passes it allows more of the heat to be transfered to the cool air as its moving and thefefore constantly cool as opposed to the air above the bonnet warming up and staying warm at a stand still.

 

Like a fan in a sunbead moving air is far better than it standing there not moving collecting the heat and not moving it on

It depends on where the areas of high and low pressure are and how the air behaves as it moves over and through the bonnet. Some designs will aid cooling, others are purely cosmetic and worse case can have a detrimental effect. It's hard to say exactly because each car is different, and the only way to tell for sure is to get the car in a wind tunnel.

anyone with experience with rx7 s will know they do make a big difference.

 

With supras, hmmm not so sure as I am not aware that engine temperatures at a standstill get so hot that it significantly inhibit performance.

 

That said, lower temperatures are always good for an engine, particularly for a turbo charged car. By that logic they can only be good.

Well thats a complete opposite of the tests that a guy on the SXOC who owns an RX7 with a vented bonnet found,

he checked temps at various points throughout the engine bay, and did comparisons with a std bonnet, and found that temps where a fair bit lower with the std bonnet, i will see if i can find it.

What about the chargespeed bonnet?

It has a vent at the front to take air in, then a few in the middle which surely forces it out?

It depends on where the areas of high and low pressure are and how the air behaves as it moves over and through the bonnet. Some designs will aid cooling, others are purely cosmetic and worse case can have a detrimental effect. It's hard to say exactly because each car is different, and the only way to tell for sure is to get the car in a wind tunnel.

Pressure is to do with the heat rising, i'm refering to the heat being transfered from molecule to molecule due to difference in temperature.. surely thats aided much more effectively with moving air

I found this thread on the supra forum:

http://www.supraforums.com/forum/showthread.php?t=373270&highlight=vented+hoods

Some more reading in this thread reg under bonnet temp etc:

http://supraforums.com/forum/showthread.php?t=307421&highlight=lower+engine+bay+temps

Well thats a complete opposite of thew tests that a guy on the SXOC who owns an RX7 with a vented bonnet found,

he placed thermocouples at various point throughout the engine bay, and did comparisons with a std bonnet, and found that temps where a lot lower with the std bonnet, i will see if i can find it.

really? I thought vented bonnets were always recommended for rx7s. Please post the article if you can find it. Would be an interesting read.

really? I thought vented bonnets were always recommended for rx7s. Please post the article if you can find it. Would be an interesting read.

I was just saw a thread on the supraforum about vented bonnet on a RX-7.Search under vented hoods.

really? I thought vented bonnets were always recommended for rx7s. Please post the article if you can find it. Would be an interesting read.

Here you go, i have amended my original post as i remembered it wrong about thermocouples, but the results are reasonably clear.

Link as there is a table that won't copy.

http://www.sxoc.com/vbb/showthread.php?t=359562

Do any benefits of a vented bonnet outweigh the extra drag caused by them in the frst place?

Intead of the air going under the car and now going over, does this cause any difference in aero balance at speed?

Maybe look at the older JGTC cars (not the silhouettes) to see what they used an learn from that.

On a purely aesthetic point of vie, most of them look like a dogs dinner.