Thread: Fors and against Bonnet scoops

Originally Posted by p38arover

And this from a "hippo" driver!




Can you imagine any other manufacturer taking the P out of themselves like this?

Ron

It must have been the "well they're going to take the p155 out of us anyway, might as well come from us" approach, have to admit not a very pretty car is it. The Freelander must be the Land Rover carpark equivalent to the fat friend the good lookers always have at the pub, it's not just there out of sympathy, it also makes the other models look more asthetically appealing.

Good on you Garrycol, someone has to take one for the team occassionally.

Anyway back to the bonnet mailbox. The scoop I mentioned earlier is on pg 144 April's Land Rover world. Looks good but at 600 pounds plus postage and handling, I think it bloody should look good.

Originally Posted by rick130

I've actually done wool tuft testing of the airflow over and around the bonnet of the 'fender and it throws up some interesting anomalies.

Rick, did you look at airflow along the sides at the back of the engine bay - around the air intake area on a defender? I would guess an outlet there, especially if flared, would have good suction.

Originally Posted by rick130

First up, a general comment on letting air out of the underbonnet area.
1. Raising the trailing edge of any vehicles bonnet doesn't let any air out. The base of the windscreen is quite a high pressure region. If you raise the trailing edge air is actually forced back in under this edge and into the engine bay. I've proven this on a number of vehicles over the years with wool tuft tests.
Remember back in the day how the A9X Torana had a rear facing bonnet scoop for the carby ? It was for this reason. Even earlier, HDT used to pack the trailing edge up on the XU1's to feed colder air to the carbies.

2. Without a wind tunnel, the best place to let hot radiator air out is fairly well forward in a place of laminar flow. Look at where the bonnet cut out is on a Lancer Evo VII, VIII, or IX or a Panoz ALMS car. Also look where the small outlets on the outside edge of the bonnet are on the Suby WRX STi WRC cars.



I've actually done wool tuft testing of the airflow over and around the bonnet of the 'fender and it throws up some interesting anomalies.
Not a lot bleeds out from around the edges of the bonnet. It appears the air flow in these regions is too strong from the front, impeding air trying to exit.

I removed the small plastic cover on the drivers wing and the flow here is strange, depending on speed. There was quite a bit of flow reversal and turbulance. Not a good spot to extract air.

The centre of the bonnet, at a point just above the t/stat housing on a 300Tdi had excellent laminar flow at all speeds, and would be my pick to place a cutout or rearward facing scoop.

But none of it really matters when you REALLY need to get the heat out, at 3kays an hour in low range, only relying on the fan

Do you know what the easiest way to ensure good air flow through a Defenders engine bay???????






Easy... remove the bonnet and put it in the back of the wagon

Yep
Go for it Dawg.
Make sure you wear your baseball cap backwards and PUMP the DOOF DOOF music BRO.
Can you place the external part of the vent on the bonnet and take a pic to show us roughly what it looks like?????
Perhaps we could make a better decision if it looks too much BLING or not.
BigBuggas D1 looked nice with the pootrol scoop.
Andrew

I think it was on this forum a long time ago.
A bloke in Northern NSW had cut about 4x2 inch or so holes in the rear corners of the bonnet.
It looked OK and would give an exit for air , in a relatively low pressure area Vs in front of that upright screen.

Regards Philip A

Originally Posted by JDNSW

I'd like to know what you base that on - there are wide gaps each side of the engine, even on a V8 leading into a large open area under the body/chassis/gearbox, which because of the shielding effect of the front axle, I would expect to have relatively lower pressure at speed, certainly lower than the pressure of air forced by the ram effect through the radiator. And this under body volume has a large exit area each side, even though the rear axle impedes the exit there.

Certainly the cross section area of the escape path down the sides of the vehicle and out underneath is vastly greater than any possible scoop on top. Of course you could always leave the bonnet off, but that has its drawbacks as well.

There may be a patch of stagnant air in the top rear of the engine compartment, but with the overall airflow through the engine compartment I rather doubt it - that air bleeds down over the bell housing and gearbox and out under the sides of the vehicle - if you don't believe me, feel the floor and transmission tunnel after a run, and no, that is not the gearbox getting hot - if its hot, it is probably from this hot air.

John

based purely on the observation of several people that the Defender appears to require the fan at speed to keep the air flowing through the radiator. I used to think that ram air alone was sufficient above 60km/h on any vehicle, however there have been a few people, myself included that have noticed that if the viscous coupling is faulty at all, the engine gets warmer than I like on a hot day. Replace the viscous clutch, everything's back to normal. It almost appears that the fan is required to force the air out of the engine bay to allow air to flow through the radiator.

Originally Posted by rovercare

But none of it really matters when you REALLY need to get the heat out, at 3kays an hour in low range, only relying on the fan

but it only seems to get hot at 100km/h ??
Fan almost seems sufficient going slow ??