Thread: Project bonnet scoop

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

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 if the attachments dont work.

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.

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?

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

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?

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 ?

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

Looks great!

The P38 - love or hate it

http://www.graemecooper.com.au/smf_f...c=3.0;attach=1