Bonnet scoop on RRC

**blackrangie** · 23rd January 2018, 03:37 PM

Originally Posted by Davo

That's it exactly, getting the air out, not in. I had educate myself in this through countless hours of reading but once I realised this, then it all became easier.

The internet is swamped by threads where guys plop a scoop on a bonnet because it "looks right", and then these threads always end with something about how it "seems to work". There's very, very little showing how someone worked it out for themselves properly. One of the best threads I found had hidden in it a couple of comments from a guy with a big racing car in America, where he'd used some aftermarket radiator intake kit that rammed more air in but only pressurised the engine bay. He got rid of it and improved the engine bay air exit and it made a huge difference for him. (And this was at something like 150mph!)

That giant scoop shown above isn't going to work because it's going to allow air through the bonnet, when you want it going through the radiator. It [I]might[I] work if all that air goes straight down the back of the engine bay and creates a low pressure area behind the radiator, but because of the amount of stuff in the way and the enormous turbulence it will cause, it won't be that straightforward. More likely is that the air tries to get into the radiator, and tries to get into the engine bay through the scoop, and the poor radiator will be stuck in the middle with not enough airflow. You can get away with a lot of this when the ambient temperature is only 20c or 25c, but as you point out it all changes with an extreme heat load, towing, and so on.

You say it wont and it might work in the same comment.

The scenerio where you say it "might work" is exactly what has been posted above as what is intended.

As nobody has ever to my knowledge tried a scoop like this on a RRC it will be a learnig experience for everyone.

The aim is to make 2 holes at back of scoop to direct air down the firewall and each side of engine and out.

Back half of inner wheel arc removed

Bonnet side rears vented.

If it doesnt work it will be blanked off and probsbly stay if it enhances the look of the car

**blackrangie** · 23rd January 2018, 03:41 PM

Originally Posted by Baggy

Hi All,

Gavin - Thanks for the offer and you are what this site is about ... great people who offer to assist where necessary

Hoping that I don't need your bonnet as I believe the GU Patrol scoop is the right balance .... its not too big.

Reading through the treads with input from Davo .... Shane and others (Thank you) my thoughts was the following.

I only cut way enough bonnet to allow the scoop to drop into position in the front.

If you look straight at the scoop opening .... my bonnet runs just below halfway through the opening of the scoop so air is split halfway flowing down the slot in the front
with the rest flowing further down the scoop into a small slot cut in the rear for a fin that runs across the back of scoop.

I cut a groove just wide enough to allow the fin (with a bit of pushing with a screwdriver) to allow it to drop in and to sit in position.

When I took it for a spin I took it up the Row highway (100 Kms) ..... 33 degree day ... got to normal operating temperature and drove fine .... in fact it
maybe wishful thinking on my part but seemed more responsive and kicked down better .... no scientific evidence and only a short run.

With the slots I was more concerned that with the airflow it would becoming this large white whistle ..... thankfully no.
My reasoning's for going minimal were the advice on pressurization ... and not to hinder the radiator .... again I have no temperature issues with this vehicle.

You can always enlarge the slots if necessary not vice versa.

I took the temperature inside cab while driving at only 70 Kms per hour .... got home while engine running checked transmission bell housing temperature and pan
from underneath vehicle with digital thermometer.

IMO ...the large bonnet scoop does fill the opening on a classic bonnet but I'm unsure how practical it will be as others have already stated.

The jury is still out for me ...... I'll drive it over the next coming months and see if there is any noticeable difference in heat from the transmission tunnel which was the reason
for this exercise.

Hoping that I don't need to contact Gavin for a bonnet .......

Cheers

Baggy

The scoop is just a scoop, its what holes are cut under it and where that count.

**blackrangie** · 23rd January 2018, 03:43 PM

Originally Posted by DiscoMick

I don't understand aerodynamics, but I was thinking that aircraft wings are shaped to cause air to flow over the top, so that causes the air under the wing to lift up, causing the wing to lift.
So if the aim is to get hot air out of the engine bay, then a bonnet should be shaped like a wing so the outside air flows over the top, while the hot air underneath is drawn up and out the rear of the scoop.
That would also cause air to be drawn thru the radiator and then up and out the rear.
Does that sound right?

Yes on bonnet sides, but cant really do legally on bonnet tops due to hot air hitting windscreen and fogging and if oil hose bursts at speed your stuffed for vision etc

**blackrangie** · 23rd January 2018, 03:47 PM

Originally Posted by Baggy

Hi All,

Here's a thought ..... looking at that large bonnet scoop for the classic from blackrangie.

If it was reversed (open at the rear) could that as others suggested on the Disco 1 forum page give a low pressure area to draw in air rather than
ramming air in from the front?

Cheers

Baggy

Not legal from what i hear. Remember the million v8 79series cruisers and patrols etc etc out there we all see with these kind of big scoops, yes the air goes through an intercooler, but it still has to exit somewhere. From what i know these cars are not experiencing overheating issues.

DiscoMick · 23rd January 2018, 04:26 PM

Originally Posted by blackrangie

Yes on bonnet sides, but cant really do legally on bonnet tops due to hot air hitting windscreen and fogging and if oil hose bursts at speed your stuffed for vision etc

I guess that's why there are so many aftermarket vents for the sides of the mudguards back just before the firewall, to exhaust air out the sides, not onto the windscreen.

**Davo** · 23rd January 2018, 07:02 PM

Originally Posted by DiscoMick

I don't understand aerodynamics, but I was thinking that aircraft wings are shaped to cause air to flow over the top, so that causes the air under the wing to lift up, causing the wing to lift.
So if the aim is to get hot air out of the engine bay, then a bonnet should be shaped like a wing so the outside air flows over the top, while the hot air underneath is drawn up and out the rear of the scoop.
That would also cause air to be drawn thru the radiator and then up and out the rear.
Does that sound right?

Yes, that is about right, but then you'll find, (as I certainly did!), that once you change one thing, everything changes. That's why car aerodynamics has so much written about it.

**Davo** · 23rd January 2018, 07:04 PM

Originally Posted by Baggy

Hi All,

Here's a thought ..... looking at that large bonnet scoop for the classic from blackrangie.

If it was reversed (open at the rear) could that as others suggested on the Disco 1 forum page give a low pressure area to draw in air rather than
ramming air in from the front?

Cheers

Baggy

If the engine bay is a low pressure area like mine, then yes, that's what would happen. But remember I've got a sort of air dam under the bullbar bumper and a rubber seal between the bonnet and body.

**Davo** · 23rd January 2018, 07:08 PM

Originally Posted by Baggy

Discomick - I like you am unsure.

The biggest difference to me would be the air flowing over a wing is not restricted.

Unfortunately under the bonnet of all cars is an area never designed for air flow efficiently except in the more exclusive marques who have
the computer modelling technology / wind tunnel for such things and where this may matter at higher speeds.

I on the other hand will have to grab my blower vac and a smoker to see if I can see where the air goes

cheers

Baggy

I've got a pedestal fan, incense sticks, and some of that liquid smoke stuff you use for smoke machines!

I soaked some cotton wool and heated it with a soldering iron. Primitive, yes, but being able to see air flow is what it's all about. I'm still scheming how to build a wind tunnel . . . until some common sense cuts in.

**Davo** · 23rd January 2018, 07:19 PM

Originally Posted by blackrangie

You say it wont and it might work in the same comment.

The scenerio where you say it "might work" is exactly what has been posted above as what is intended.

As nobody has ever to my knowledge tried a scoop like this on a RRC it will be a learnig experience for everyone.

The aim is to make 2 holes at back of scoop to direct air down the firewall and each side of engine and out.

Back half of inner wheel arc removed

Bonnet side rears vented.

If it doesnt work it will be blanked off and probsbly stay if it enhances the look of the car

Alright, keep your pants on, the "won't work" comment is based on some actual knowledge and the "might work" comment is based on guesswork. You could well get a good result but it depends completely on that low pressure working as you want it to, which means everything has to be just right, which - and believe me, I've spent a few years on this - takes about equal parts research and luck! Unfortunately to measure these changes it takes a lot of finicky work which most of us just don't have the resources for.

And yes, someone else has done something similar with a Range Rover and they reckoned it worked. Of course, it looks cool anyway.

**blackrangie** · 23rd January 2018, 10:31 PM

Originally Posted by Davo

Alright, keep your pants on, the "won't work" comment is based on some actual knowledge and the "might work" comment is based on guesswork. You could well get a good result but it depends completely on that low pressure working as you want it to, which means everything has to be just right, which - and believe me, I've spent a few years on this - takes about equal parts research and luck! Unfortunately to measure these changes it takes a lot of finicky work which most of us just don't have the resources for.

And yes, someone else has done something similar with a Range Rover and they reckoned it worked. Of course, it looks cool anyway.

Who has and have you got photos?

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