Project bonnet scoop

[glenhendry]

I see and read everywhere that heat is the RR's natural enemy. I hear about fuse boxes succumbing, and very high underbonnet temperatures. When we are moving, I am sure the temps are fine under the bonnet as the air coming through the radiator and grill are pushed downwards by the firewall and under the car, but when the car stops, all the heat just sits there and cant escape due to the clamshell bonnet. The RR classic had a scoop/vent I believe and the P38 overfinch too, I think it will be a good move. I am all for original looking P38s in terms of bumpers etc, but a low profile scoop/vent might look nice and if I hate it, I can just get a new bonnet.

I have bought a bonnet scoop (http://www.ebay.com.au/itm/360413474558'ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649) and am going to install. I will post pics along the way. My bonnet's paint is pretty crap anyway so I dont have too much to lose.

My question to the group is, facing forwards or backwards. My main aim is to allow heat to escape upwards when the car is turned off and parked. I think my default decision will be rear facing. Comments welcome.

[Mick_Marsh]

Opening backwards towards the windscreen of course.
Maybe even put vents (http://image.shutterstock.com/display_pic_with_logo/120493/120493,1289224881,1/stock-photo-metal-surface-with-air-vent-perforation-64641367.jpg) in the top of the bonnet scoop.

[p38arover]

Place it on the bonnet and take some pics facing both ways for us to critique.

Why not face it forward to get a little more air through the engine bay when driving?

[Mick_Marsh]

Place it on the bonnet and take some pics facing both ways for us to critique.

Why not face it forward to get a little more air through the engine bay when driving?
If you face it forward, the air entering will be competing with the air coming through the radiator for an escape route. This may result in less air passing through the radiator and possible overheating.

[Pedro_The_Swift]

Backwards,,

will also let more noise out,,
would LOVE to see some before and after (where??) temps--

[33chinacars]

Maybe something like this would have been better at getting heat out from under bonnet.

UNIVERSAL FIBREGLASS BONNET VENTS PICK UPS WELCOME | eBay (http://www.ebay.com.au/itm/UNIVERSAL-FIBREGLASS-BONNET-VENTS-PICK-UPS-WELCOME-/150772236717?pt=AU_Car_Parts_Accessories&hash=item231ab9c1ad)

Usually a low pressure area at the base of the windscreen. so if you put your scoop facing backwards it will draw air into engine bay. As it did on A9X Torana's. These were blanked off from the engine bay on the racecars & only fed the air cleaner etc.

Gary

[benji]

I would have thought facing foward would be the best option. It would allow heat to escape whilst sitting in traffic, and direct air into the engine bay whilst moving. The air vents in the classics were behind the bonned, and directed air into the cabin. I think the main difference is, the p38's have a seal around the outer edge of the bonnet, so the heat cannot escape.

[whisky_mac]

I like the vents in the front guards on the L322s, maybe you could modify them to fit the P38.

[p38arover]

I like the vents in the front guards on the L322s, maybe you could modify them to fit the P38.

I think it would be easier to fit RRS vents. I have some pics here and will post them a bit later.

But both would need under-guard / inner guard mods. The scoop is much easier.

[wayneg]

I have seen a couple of Classics with vents cut into the rear sides of the bonnet. Maybe thats an option
Something like these......http://www.ebay.com/itm/Auto-Truck-SUV-Universal-Black-Mesh-Air-Intake-Duct-Side-Vents-Hood-Fender-2-Fin-/180854003677?pt=Motors_Car_Truck_Parts_Accessories&hash=item2a1bbd17dd&vxp=mtr

[brend0n]

I've fitted a side vent.

very easy to do and I think looks the goods on the RRCs. (I realise this is for a P38)
I'm considering adding vent to the bonnet (similar to the ones Mick_marsh put up) to help the air con and other electrics out. however these will be towards the edges to ensure hot air doesn't go straight into the interior vent.

I have no number evidence but I can tell its working cause driving along if i put my hand out in the path of the vent I can feel quite hot air coming out

[BigJon]

I've fitted a side vent.


I have no number evidence but I can tell its working cause driving along if i put my hand out in the path of the vent I can feel quite hot air coming out

Mine is the same but different. I fitted my vent into the side of the bonnet itself.

[33chinacars]

Have seen RRS vents in the sides of a P38. Looks pretty good to me. I think it would work better than a bonnet scoop. Most bonnet scoops are for getting air into the induction system not for getting air out.

.Gary

[wayneg]

I've fitted a side vent.

very easy to do and I think looks the goods on the RRCs. (I realise this is for a P38)
I'm considering adding vent to the bonnet (similar to the ones Mick_marsh put up) to help the air con and other electrics out. however these will be towards the edges to ensure hot air doesn't go straight into the interior vent.

I have no number evidence but I can tell its working cause driving along if i put my hand out in the path of the vent I can feel quite hot air coming out

Thats exactly what I was getting at. Seems quite a common mod on Classics.
Even works as a hand warmer too.

[996TURBO]

I removed my bonnet insulation foam and hood front and side rubber channel (not the rear one near the bulk head or the bulk head foam will hang).

That helps a lot and i can see the heat coming out when it's raining and cold outside.

A friend of mine put some spacers under the hinges to lift the back of the bonnet. Works well.

But you'll have more noise.

[jakeslouw]

Would this work for the Defender?


The Rover V8 puts out a fair bit of heat, and once the hot air is up under the bonnet, it has nowhere to go.

I've seen some Defender bonnets with a set of holes on the rear / side portion of the Defender bonnet, probably cut using a 50mm hole saw.
Or would a set of rear-facing louvers/slats work?

[d@rk51d3]

Looking to put some side vent into my RRC too.

Apparently cutting them into the bonnet will lead to rust.
Better to fit them in the ally panel behind the bonnet.


Here's an interesting concept:
http://www.landroversonly.com/forums/f8/3rd-generation-side-vents-classic-32899/

[33chinacars]

Yes louvers in rear of bonnet would work. Just as lifting the rear of the bonnet also. Something we all did on our hot Holdens & Falcons 30 + years ago. So nothing new there. Didn't do much for the air coming into the cab tho. Its was like a furnace. Hot Dam Hot

Gary

[DT-P38]

There is a modified black p38 "expedition style" on ebay UK last week or so that has similar vent to GlenHendry's suggested one mounted rear facing that looked quite nice. Not sure about escaping air going into cabin vents under plenum though. Not qualified in aerodynamics but am certain about that low pressure area at base of windscreen drawing air out at speed.

Have also been thinking about removing rubber seal from rear of under bonnet along with those foam bits on the rear outer sides that wrap around the bonnet struts. Again, not sure about hot air being directed into cabin plenum vents... especially in summer when you would want it out of under bonnet most but in cab least. So may just try taking the foam side bits out in hotter times.

I like the idea of having GlenHendry's one rear facing and shut-able... but also like the other vent style ones from Ipswich mounted to the rear outer top sides of the bonnet. In saying all that, I also like the idea of getting my thermo fans pushing air through the radiator whenever the car is stationary or at slower than approx. 40km/h.

As with anything P38... decisions, decisions, decisions!

FANTASTIC someone is having a crack though! Good onya Glen.

[DT-P38]

And has anyone considered ramifications of removing positive pressure under clam shell? Not that I would want to test it, but perhaps it is for protecting stuff if that far into water for brief but deep water crossings.

Or was the P38 clamshell purely a styling exercise?

[Scouse]

I was out at John Davis Motorworks years ago (pre-P38 RR) & he was building a widened & lengthened RR Classic for the Saudis.
He had 2 fan motors fitted at the rear of the engine bay to forcefully extract the hot air from the engine bay. It might be overkill for some but I'm sure it worked.

[rangieman]

I know some of you p38 guys do go off road and some dont or wont ;), I would tread carefully anyone that likes off road use with scoops that face rearward , As soon as you enter a bog hole or puddle any steam created under the bonnet from water and heat will come back towards the screen = loss of vision for said period of time not good in my opinion:cool:

[poleonpom]

This is still on my list to do. If it mucks with the airflow I'll just stick a choke on it and if that doesn't work, perhaps the addition of a small chimney so I can brew a cup of tea whilst "off road":D

[DT-P38]

I know some of you p38 guys do go off road and some dont or wont ;), I would tread carefully anyone that likes off road use with scoops that face rearward , As soon as you enter a bog hole or puddle any steam created under the bonnet from water and heat will come back towards the screen = loss of vision for said period of time not good in my opinion:cool:

Thanks Rangieman. I reckon they need to be closable to avoid this. Or get out the gaffer tape before hitting the water!

[DT-P38]

Photo's of the one I refered to earlier.

BTW it sold in the UK last week for GBP2,150 (AUS$3,309.63).

[Keithy P38]

That pod filter would go well when wading ;-)

[whisky_mac]

Photo's of the one I refered to earlier.

BTW it sold in the UK last week for GBP2,150 (AUS$3,309.63).

The vent that interests me is the side vent, I would not install the bonnet vent but the side vent I would.

[Scouse]

Yes, but fit a RH vent to the RH side rather than what he's done.

[33chinacars]

Yes, but fit a RH vent to the RH side rather than what he's done.


Thanks Scouse wondered why it looked so pox

Right way they look good

Gary

[PeterAllen]

Does that UK car photo have an exhaust van installed on the bonnet vent or do I need glasses (stronger glasses)??

[p38arover]

Does that UK car photo have an exhaust van installed on the bonnet vent or do I need glasses (stronger glasses)??

Dunno about a van but certainly a fan. :p

[PeterAllen]

Well I did say I needed glasses?
Thanks Ron for confirming. I thought I could see a van in the fent:D

[glenhendry]

I have scoop. Here are some front and back photo for our discussion, even though Mick suffixed his opinion with "of course" which must mean we are all silly for considering any other option :)

I think it looks cooler and tougher forward, but I think I prefer the subtle lines of rear facing which matches the RR styling more closely.

Sorry the photos arent great. Link here (https://picasaweb.google.com/105878078807082914833/RRBonnetScoopOptions?authkey=Gv1sRgCK6Dkam8rPyy0AE ) if the attachments dont work.

[rick130]

A couple of little tips on bonnet aerodynamics.

A rearward facing scoop near the base of the windscreen won't let air out, it pushes air back under the bonnet.

Why ?

The base of the windscreen is a high pressure zone.

This is how the bonnet scoop worked on the A9X Torana, feeding nice, high pressure air to a sealed airbox and how the vents in the valence panel work on most all cars.

You can prove this for yourself by taping wool tufts along the trailing edge of the bonnet and lift the rear of the bonnet with spacers (I realise this is hard on a RRC)
I can guarantee the tufts will all flow back under the bonnet.

Forcing air into the engine bay from a bonnet scoop will reduce the amount of air flow through the radiator when moving too.

Air will only flow from a high pressure region to a low pressure region.

Sometimes even the fan is needed to create a low pressure region behind the radiator to create flow and hence cooling.

Defenders and GU Patrols are notorious for this.
If the viscous fan starts to fail they overheat at speed, right where you'd think ram air should be forcing air through the radiator.
The radiator fan, instead of pulling air through the rad actually appears to be pushing air from the underbonnet region in these cases.

If you add a generic scoop to push air into the underbonnet area, you are increasing the underbonnet air pressure.

If you want to try and help evacuate under bonnet air, vents and louvres near the front but behind the radiator to mid bonnet length appear to work well.
Think of where cars like Lancer Evo's have their bonnet vents positioned.
The manufacturer has spent serious wind tunnel time getting their airflow correct.

Generally speaking you want an area of laminar flow, not disturbed air to use and try to extract air from under the bonnet.
Use wool tufts taped in place to see how the flow looks, you might be surprised ;)

Vents behind the front wheels in the guard seem to work well too, even though airflow there is disturbed.

[glenhendry]

Very interesting, thanks Rick. My main aim to to allow hot air to escape engine bay (and especially upper engine-bay, ie fusebox area) once the car is stopped and parked. Since we are always hearing about high engine bay temps I dont like the thought of all our wiring, relays, EMS computer, battery and fuse boxes baking under there for the 2 hours is takes for it to dissipate.

Having said that, I dont want to screw up my airflow while I am driving either! Now what to do?

[Pedro_The_Swift]

I wonder if the area the windshield wiper motors sit in (tech term please) could be used,, I would think it fits into Ricks high pressure area,,
but its a perfect spot to extract hot air from the rear of the engine bay

[Pedro_The_Swift]

so we cant go out the top,,
and in the D2 the sides are a bit busy,,
so that just leaves underneath??

Do full length sump guards help or hinder this?

[rick130]

Louvres half way down the bonnet, either along the edges near the guards or in the centre.

They look pretty and let the hot air out, either when moving or stationary.





Is heat soak a real problem ?

or are you all fixing a problem that may more perception than reality ?

Has anyone actually logged underbonnet temps with a data recorder to see if it is a problem ?

[LavisLane]

Aerodynamics aside - i like the look of the one on this link :twisted:

Looks great!

The P38 - love or hate it (http://www.graemecooper.com.au/smf_forum/index.php'topic=3.0)

http://www.graemecooper.com.au/smf_forum/index.php?action=dlattach;topic=3.0;attach=1

[Hoges]

a simple time /thermostat delay switch to run the electric fans on very hot days to reduce heat sink might do the trick Glen without the need to cut metal. I had a V6 Calibra (alas no more :dbcry:) with this feature and it worked well. Have thought about it for the P38 but am unsure how to install...