Bonnet Scoop/Vents

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Mrbaboon1985
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Bonnet Scoop/Vents

Post by Mrbaboon1985 » Fri Oct 09, 2020 9:54 am

After a bit of help/advice.

Looking for a bonnet scoop or some vents and wondering if anyone has fitted similar and where you got them from.

Sone videos seem to be show drilling holes in the bonnet and fitting the vent or scoop over that area?

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Re: Bonnet Scoop/Vents

Post by Noel » Fri Oct 09, 2020 10:13 am

If the scoop or vent needs to actually function and deliver air into the engine bay, then yes significant holes will need to be made in the bonnet - so any video suggesting that would be correct to my mind.

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Re: Bonnet Scoop/Vents

Post by Major_Tom » Fri Oct 09, 2020 11:07 am

A better solution I've seen on many Capris is to plumb in a bit of ducting from one of the lower holes in le valence to the carb.
I'm the one that leaves all those shoes in the carriageway.

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Re: Bonnet Scoop/Vents

Post by Mrbaboon1985 » Fri Oct 09, 2020 11:22 am

Thanks both for the replies I do like the the look it gives the car having a scoop or vents but want the functionality too.

Ill watch some more videos on best placement and see if u can get some ideas on what other owners have done

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Re: Bonnet Scoop/Vents

Post by D366Y » Fri Oct 09, 2020 11:32 am

I think it depends how big you're thinking of going and how big it really needs to be?

Seen a few people modify the bonnet bulge already on the car and put a vent in that which I thought was rather clever
13040584c3fb7aaba0.jpg
A wise man once said... "you can never have too many capris - buy another" :beer:

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Re: Bonnet Scoop/Vents

Post by Bug » Fri Oct 09, 2020 1:21 pm

If you have a basic understanding of aerodynamics and fluid flow, then maybe you'd consider the other option.
Instead of trying to force more air into the engine bay, which will need to displace what is already there, you could consider raising the rear edge of the bonnet instead. The airflow over the top of the bonnet tends to move faster and therefore reduces pressure (one of the reasons that the steering goes light at higher speeds, though the uninitiated will try to convince you its all due to air being forced under the front).
As the air pressure above the bonnet is lower, it will have the effect of sucking the hot air out from the engine bay, allowing more cold air to enter through the normal intakes at the front. This is actually more effective than the ram air approach of an intake.
Then we get into all sorts of discussions on boundary layer control, where the hot air exiting the engine bay serves to smooth the flow over the car, thus making it move faster with less turbulence, lowering the pressure even more and improving the extraction rate from the engine bay.
Of course, raise the rear of the bonnet too high and you cause the flow over the bonnet to stall, increasing turbulence and lessening the extraction effect.

If that has lost you then just cut an effin' great hole in the bonnet :xd:

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Re: Bonnet Scoop/Vents

Post by Lord Flasheart » Fri Oct 09, 2020 1:39 pm

Bug wrote:
Fri Oct 09, 2020 1:21 pm
If you have a basic understanding of aerodynamics and fluid flow, then maybe you'd consider the other option.
Instead of trying to force more air into the engine bay, which will need to displace what is already there, you could consider raising the rear edge of the bonnet instead. The airflow over the top of the bonnet tends to move faster and therefore reduces pressure (one of the reasons that the steering goes light at higher speeds, though the uninitiated will try to convince you its all due to air being forced under the front).
As the air pressure above the bonnet is lower, it will have the effect of sucking the hot air out from the engine bay, allowing more cold air to enter through the normal intakes at the front. This is actually more effective than the ram air approach of an intake.
Then we get into all sorts of discussions on boundary layer control, where the hot air exiting the engine bay serves to smooth the flow over the car, thus making it move faster with less turbulence, lowering the pressure even more and improving the extraction rate from the engine bay.
Of course, raise the rear of the bonnet too high and you cause the flow over the bonnet to stall, increasing turbulence and lessening the extraction effect.

If that has lost you then just cut an effin' great hole in the bonnet :xd:
Excellent summary Mr Bug :D

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Re: Bonnet Scoop/Vents

Post by D366Y » Fri Oct 09, 2020 4:21 pm

Bug wrote:
Fri Oct 09, 2020 1:21 pm

Then we get into all sorts of discussions on boundary layer control, where the hot air exiting the engine bay serves to smooth the flow over the car, thus making it move faster with less turbulence, lowering the pressure even more and improving the extraction rate from the engine bay.
Of course, raise the rear of the bonnet too high and you cause the flow over the bonnet to stall, increasing turbulence and lessening the extraction effect.
What is the exact measurement of how much the rear bonnet needs to be raised then? I'm sure wit your expertise in the field and very detailed explanation you can do the maths for us!! :D :poke:
A wise man once said... "you can never have too many capris - buy another" :beer:

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Re: Bonnet Scoop/Vents

Post by Mrbaboon1985 » Sat Oct 10, 2020 4:13 pm

D366Y wrote:
Fri Oct 09, 2020 11:32 am
I think it depends how big you're thinking of going and how big it really needs to be?

Seen a few people modify the bonnet bulge already on the car and put a vent in that which I thought was rather clever 13040584c3fb7aaba0.jpg
I do like that, I wonder where they got the vents for the bulge or whether that's just cut straight into the bulge with no cover inside?

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Re: Bonnet Scoop/Vents

Post by Mc Tool » Sat Oct 10, 2020 10:23 pm

Bug wrote:
Fri Oct 09, 2020 1:21 pm
If you have a basic understanding of aerodynamics and fluid flow, then maybe you'd consider the other option.
Instead of trying to force more air into the engine bay, which will need to displace what is already there, you could consider raising the rear edge of the bonnet instead. The airflow over the top of the bonnet tends to move faster and therefore reduces pressure (one of the reasons that the steering goes light at higher speeds, though the uninitiated will try to convince you its all due to air being forced under the front).
As the air pressure above the bonnet is lower, it will have the effect of sucking the hot air out from the engine bay, allowing more cold air to enter through the normal intakes at the front. This is actually more effective than the ram air approach of an intake.
Then we get into all sorts of discussions on boundary layer control, where the hot air exiting the engine bay serves to smooth the flow over the car, thus making it move faster with less turbulence, lowering the pressure even more and improving the extraction rate from the engine bay.
Of course, raise the rear of the bonnet too high and you cause the flow over the bonnet to stall, increasing turbulence and lessening the extraction effect.

If that has lost you then just cut an effin' great hole in the bonnet :xd:
I dont get this , I mean the whole raising of the rear of the bonnet has a lot of potential bonuses , like all the stuff you said, and more engine noise ...but :xd: Im thinkin that my heater/vents flows a lot of air, without the fan once I have a bit of road speed .......so I always figured that area at the base of the screen was relatively high pressure . I guess that if the under bonnet pressure was even higher it would work. Makes you think :headscratch: there are some significant differences in pressure around a vehicle at speed.
Next time your driving in the rain have a look at how the water on the bonnet behaves at different speeds :)
you gotta make the most :cheers: :cigar: :burnout: out of your 20's, 30's, and 40's coz when you hit 50 the "engine check" light comes on. :?

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Re: Bonnet Scoop/Vents

Post by Bug » Sun Oct 11, 2020 12:01 pm

D366Y wrote:
Fri Oct 09, 2020 4:21 pm
Bug wrote:
Fri Oct 09, 2020 1:21 pm

Then we get into all sorts of discussions on boundary layer control, where the hot air exiting the engine bay serves to smooth the flow over the car, thus making it move faster with less turbulence, lowering the pressure even more and improving the extraction rate from the engine bay.
Of course, raise the rear of the bonnet too high and you cause the flow over the bonnet to stall, increasing turbulence and lessening the extraction effect.
What is the exact measurement of how much the rear bonnet needs to be raised then? I'm sure wit your expertise in the field and very detailed explanation you can do the maths for us!! :D :poke:
Well I reckon ,it's a bit, plus a smidge, then maybe tweak it by a gnat's cock.

Tip: If you can't see the road then it's maybe too much. ;)

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Re: Bonnet Scoop/Vents

Post by STEVEW » Sun Oct 11, 2020 3:45 pm

Hi Mrbaboon1985
Looking for a bonnet scoop or some vents and wondering if anyone has fitted similar and where you got them from.
Why do you want to do this?
Is it for aesthetics or of a practical purpose?
One problem I have is with the words, “scoop” and “vent”.
To me the former suggests you want air into the engine bay and the latter that you wish to extract it.

Regards,
Steve

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Re: Bonnet Scoop/Vents

Post by STEVEW » Sun Oct 11, 2020 4:09 pm

Hi Major
A better solution I've seen on many Capris is to plumb in a bit of ducting from one of the lower holes in le valence to the carb.
This is what I’ve done to a Mk 3 with a 2.3 V6.

The idea behind this was to try and get a small increase in power: the cooler the air the more fuel you can add.
On this Mk 3 the inlet for the standard air filter housing sits just above the exhaust manifold on the right hand side.
Last week the car was put through the equivalent of the MOT and the engine bay temperature was measured at 95°C.
This problem of hot air being sucked directly into the air cleaner was solved by ducting the air from behind the grill under the horn and up to a modified standard air cleaner snout.

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Re: Bonnet Scoop/Vents

Post by STEVEW » Sun Oct 11, 2020 4:48 pm

Hi Major Tom again!
I've finally been able to post a photo of the intake system thanks to Beakster.
[20201011-181727.jpg](https://postimg.cc/B8hqwLS8)

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Re: Bonnet Scoop/Vents

Post by Major_Tom » Sun Oct 11, 2020 8:11 pm

Bug wrote:
Fri Oct 09, 2020 1:21 pm
If you have a basic understanding of aerodynamics and fluid flow, then maybe you'd consider the other option.
Instead of trying to force more air into the engine bay, which will need to displace what is already there, you could consider raising the rear edge of the bonnet instead. The airflow over the top of the bonnet tends to move faster and therefore reduces pressure (one of the reasons that the steering goes light at higher speeds, though the uninitiated will try to convince you its all due to air being forced under the front).
As the air pressure above the bonnet is lower, it will have the effect of sucking the hot air out from the engine bay, allowing more cold air to enter through the normal intakes at the front. This is actually more effective than the ram air approach of an intake.
Then we get into all sorts of discussions on boundary layer control, where the hot air exiting the engine bay serves to smooth the flow over the car, thus making it move faster with less turbulence, lowering the pressure even more and improving the extraction rate from the engine bay.
Of course, raise the rear of the bonnet too high and you cause the flow over the bonnet to stall, increasing turbulence and lessening the extraction effect.
Wow!!

So do those RS type fibreglass front valances for Capris do anything?
I'm the one that leaves all those shoes in the carriageway.

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Re: Bonnet Scoop/Vents

Post by STEVEW » Mon Oct 12, 2020 7:49 am

The Major wrote:So do those RS type fibreglass front valances for Capris do anything?
Nah!
Zakspeed increased the frontal are of their go-faster Capri by about 50% with a massive air dam to prevent shoes, which are left on the carriageway by people like you, wiping out the steering rack gaiters. :D

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Re: Bonnet Scoop/Vents

Post by Bug » Mon Oct 12, 2020 11:42 am

Major_Tom wrote:
Sun Oct 11, 2020 8:11 pm
Bug wrote:
Fri Oct 09, 2020 1:21 pm
If you have a basic understanding of aerodynamics and fluid flow, then maybe you'd consider the other option.
Instead of trying to force more air into the engine bay, which will need to displace what is already there, you could consider raising the rear edge of the bonnet instead. The airflow over the top of the bonnet tends to move faster and therefore reduces pressure (one of the reasons that the steering goes light at higher speeds, though the uninitiated will try to convince you its all due to air being forced under the front).
As the air pressure above the bonnet is lower, it will have the effect of sucking the hot air out from the engine bay, allowing more cold air to enter through the normal intakes at the front. This is actually more effective than the ram air approach of an intake.
Then we get into all sorts of discussions on boundary layer control, where the hot air exiting the engine bay serves to smooth the flow over the car, thus making it move faster with less turbulence, lowering the pressure even more and improving the extraction rate from the engine bay.
Of course, raise the rear of the bonnet too high and you cause the flow over the bonnet to stall, increasing turbulence and lessening the extraction effect.
Wow!!

So do those RS type fibreglass front valances for Capris do anything?
Yes they do Tom, hence the bit where I said 'one of the reasons'.
Aerodynamics is complicated in the extreme and to be honest, without seeing evidence in a wind tunnel, the theory does not always work exactly that way in the real world.
Very basically, the air that meets the front of the car splits and tries to get to the back at the same time, regardless of how far it has to travel.
As Mr Bernoulli pointed out, if it travels faster, it cools and pressure reduces. (Similar to the venturi principle that makes carbs work).
So you'd expect the car to act like an aerofoil and lift, but there is so much rubbish under a car that the air under it swirls and disrupts the flow.
The air dam basically diverts a lot of the air down the sides instead, where it has an easier journey to the back of the car.
Less air is left to pass under the car. Imagine a crowd of people trying to get through a small space. If you send most of them round the outside then the few that are left to go through the gap have a much smoother trip.

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Re: Bonnet Scoop/Vents

Post by Bug » Mon Oct 12, 2020 11:46 am

Just to add to the aero confusion, Ford discovered that over about 25mph, sufficient cooling air got to the radiator through the lower vents in the front valance.
Therefore, they created the Mk3 grille with aerofoil sections, not to speed air through the rad, as many believe, but to stop that air going through at all, sending it up over the bonnet instead.
Which is why, even with hotter temps under the bonnet, Tickford happily blanked off the front grille completely.

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Re: Bonnet Scoop/Vents

Post by Major_Tom » Mon Oct 12, 2020 9:27 pm

Facinating stuff. So the air being forced underneath is why some folk cut holes, or straight up cut out, the rear valence? That must act like a big aerodynamic hook.

Having no gear gaiter, I've found that with the windows open, air comes shooting up through there at speed, but with all windows closed, it sucks air out of the cabin almost as readily.
I'm the one that leaves all those shoes in the carriageway.

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Re: Bonnet Scoop/Vents

Post by D366Y » Tue Oct 13, 2020 8:00 am

Mrbaboon1985 wrote:
Sat Oct 10, 2020 4:13 pm
D366Y wrote:
Fri Oct 09, 2020 11:32 am
I think it depends how big you're thinking of going and how big it really needs to be?

Seen a few people modify the bonnet bulge already on the car and put a vent in that which I thought was rather clever 13040584c3fb7aaba0.jpg
I do like that, I wonder where they got the vents for the bulge or whether that's just cut straight into the bulge with no cover inside?
I'm not sure how it's been done but I've seen a few people do it - I'd imagine if you cut straight through the bulge you could just stick some gauze/mesh or similar on the inside of the bulge to catch any crap from going straight into the top of the carb?

Something else I've seen is cutting the whole bonnet bulge off and adding in some metal to increase the height and leaving that gap as well at the same time - have a look at this link https://www.fordcapriforum.com/forum/vi ... &start=140
Cut the bulge off, put some metal in to make it higher but kept the same shape, just taller to fit the V8 in. You could theoretically do a similar thing but rathe than fill in to increase the height, just leave it open to air?
A wise man once said... "you can never have too many capris - buy another" :beer:

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