Thread: Bonnet scoop on RRC

Originally Posted by Baggy

I saw Tombie scoop .... looks like its off a Toyota hilux and its achieved (OK no scientific evidence) what I'm aiming for.
I've been toying with this for a while ....so I've bitten the bullet and picked up a S/Hand GU Patrol (2010) bonnet scoop today ... and its white

I'll start fitting it tomorrow ..... worst case scenario ....... I'll need a new bonnet.

cheers

Baggy

Good thinking, and I'm watching with much interest for my RRC - and possibly application for my D2, even though different to the D1 thread.

Worst case scenario - I have a green 93 RRC bonnet in my collection with your name on it waiting for you - maybe initially even use that for the trials rather than your white one? Don't recall any under bonnet dam on my wreck either though.
Cheers Gavin

PS, I'll probably get howled down, but didn't notice much change when DazzaTD5 took my driving lights off for a heat trial about a year ago, and I would have put any change down to removing the waterbra mesh that was also fitted at the time. Roll on the Saudi grill!!

Originally Posted by Baggy

Hi All,

Things to note on a GU Patrol scoop ..... The're not evenly shaped and add to this that a Rangie bonnet (ribs underneath) are not spaced evenly.

The washer sprays on the bonnet aren't spaced evenly .... so after much measuring ..... checking ..remeasuring and checking attached is photo of fitted scoop.

I've only just cut away enough metal as necessary for the scoop to sit in the bonnet ..... and has two slots as the back of the scoop has a plastic flange that also
recesses into bonnet taken measurements.

I had concern's about pressurizing under the bonnet and my thoughts is that I can cut away more metal if necessary for larger slot for increased air flow if necessary.

I checked an old post back on this site in 2016 when I first voiced my concerns on heat from transmission tunnel.
I'd purchased a digital thermometer and had taken readings from the bell housing and gearbox .... readings where 74 deg C

Took it for a run to Bunnings today ...... normal operating temperature and about 33 Degrees in Perth.
Temperature inside cabin driving ... transmission reading 42 deg at radio and 38 deg at transmission tunnel.

Engine temperature (dashboard gauge only) still sitting on just below halfway mark as always.

I'll keep monitoring it but very happy with outcome and I don't think the scoop has detracted from the vehicle.

I've plans to respray the bonnet and cowling in front of windscreen so that it will be the same colour for now it does not look out of place.

Baggy

Any 110kph results?

What speed was this test?

Originally Posted by blackrangie

Any 110kph results?

What speed was this test?

Tests while towing ie: heavy heat load as well please

There has been all sorts of stuff tried to cool the underbonnet area of a citroen DS (the real one, not the modern lumps of plastic excrement)... The later the cars with more stuff under the bonnet, the hotter they run. The radiator size and quality seems to make little difference... neither do vents/scoops. Someone worked out the issue was the ability for air to exit the underbonnet area. On the later cars, add in underbonnet heat shielding, extra plumbing, bigger engines ... more heat. but less space behind the engine to allow the pressurised air entering the underbonnet area .... to exit.

I wonder if that is where we start running into problems.... the ability to allow the heated air to vent from the underbonnet area ?

seeya,
Shane L.

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.

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.

that was my thinking too. as it's a big scoop. In slow moving traffic I reckon it'll work well.... as the air will exit from there. at speed it'll make a high pressure zone in the engine bay ... infact if the pressure in the engine bay is close the pressure of the air entering the radiator. the radiator will have zero cooling air flow...........................

seeya,
Shane L.

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

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?

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