thanks cockie - I never thought about it as being so complicated! Attached is a photo of my S1 just before I sold it - prior to this I also had the rear of the bonnet jacked up with spacers and I had thought with this arrangement there would be a good flow of cool air into the engine bay removing heat...but maybe not! The 200Tdi obviously allowed a lot more space under the bonnet and therefore presumably easier to "flush" hot air out with cool air coming in through a bonnet scoop. The Td5 is a very crowded engine bay, so yes, probably best to have rear-facing scoop to let rising hot air out...

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My old man had a GU scoop on his 87 Rangie, it did not make any difference to engine performance. It looked great and let heaps of dust and sand make its way into the engine bay. The amount of extra dust and dirt that made its way into the engine bay is enough for me not to do this sort of thing.

Is your engine actually getting too hot? Something I am going to do, when I get the motivation, is to create a very crude water spay system. I am going to use an old washer motor, mount the water jets on the back of the bull bar and use a blinker relay to make it spray intermitted. This should let the water actually evaporate and take heat from all of the radiators and intercooler. Switch it on when I am going up a very big hill or doing a overtake in the heat.

QLDMIKE your dads Nissan GU front facing scoop on his 87 Rangie not making any difference to his engine performance experiance or worsening it with dust etc seems to support my thoughts on this subject.

If you read my post carefully you will see it is not about about ramming air (dust and water etc) into the engine bay but all about removing heated air out of the engine bay.

I reakon if your Dad reversed his Nissan GU scoop so it was pointing backwards and it was at least located half way between screen and bonnet front then IMHO I think his performance results would have been very different.

Thats true i thought of that after i posted

TIM.

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1985 110 county 3.9 isuzu (Dads)
1992 200tdi disco (silver) (Dads)
1992 200tdi disco (green) (Mine)
http://img215.imageshack.us/img215/2...s003fw9.th.jpg

TIM.

Slunnie and Long Stroke are right about real experiences being required, I am hoping those will be forthcoming and help show how air movement in and out of a Disco engine bay relies heavily on a careful a pressure differential balance.

For instance putting aside turbo’s and intercooler requirements does wacking in a "forward facing scoop" located around halfway cause greater pressures inside the engine bay to the extent of reducing air flow through the radiator by raising inside pressure (because air inside can’t exit fast enough) and therefore vents are required either forward on bonnet (where inside to outside differential should be the highest) and or side mounted vents?

Alternatively does mounting exactly the "same scoop but in reverse" and a bit further back on bonnet towards screen and in higher pressure area allow a significant but manageable amount of extra fresh air to enter engine bay without raising engine bay pressure and having no effect on through radiator flow, hence no need for additional venting?

A frustrating subject.

I've run through the procedure of looking at removing heat from under the bonnet with my V12 Jaguar XJ-S - it's a much bigger problem than a Disco :-)

You need to be scientific about it:

First off - do the "wool tuft" test - stick lots of litt bits of wool on the bonnet about 2" long. When you drive a various speed you will see the centre of pressure move forwards and backward along the bonnet. At low speed, you may find a negative pressure just behind the radiator, and at high speed a high pressure at the base of the windscreen.

Next to to buy a Dwyer Magnehelic gauge- it measures differential pressure - it is very sensitive used in the A/C industry.

Use it to measure the differential pressure to see if you actually have a problem.

Here's a few articles.

Here is an article on Autospeed:
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Iain
300Tdi Brisbane

Iain those 2 Autospeed articals have got some good stuff in. I located Part 3 which goes into differential pressure in a lot of detail noting this test car has a Intercooler which is right up Feraldisco/Td's ally.

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I off to find a man with a "Dwyer Magnehelic Gauge"

It is very good to take a scientific approach. Before going to a lot of trouble however lets use the facts that we do know an analyse them. Frontal area of vehicle feeding radiator about 0.8 x 0.5 = 0.4 m sq area of aperture forward facing scoop 0.15 x 0.05 = 0.0075 m sq. There is a huge difference in intake area so even if the pressures were the same at the front of the radiator and at the scoop the volume of air coming in through the radiator is going to make the amount of air coming in through the scoop appear insignificant. Althought the radiator, i/c and a/c will all act to block the aperture the fan(s) will all be working to compensate.

In the grand scheme of things the amount of air pulled in by a scoop will be like a drop in the ocean. A scoop will have a localised effect as it will bring cold air into the engine bay so what ever is directly in line of the scoop will get some local benefit (top mounted i/c or cold air feed into the combustion system). These local benefits are maximised by segregating the air from the scoop and that already under the bonnet.

As for letting air out! Yes hot air rises however the amount of air pushed by the fans out through the bottom of the engine bay will once again be much greater than any air escaping through a scoop. Raising the bonnet will provide a much greater area for the air to escape that any scoop.

Good luck with it.

Hi,

Why not just use twin thermo fans and be done with it? Cost you about $250 with adjustable temp switches.

Keeps a Chev happy behind a stock RRC radiator for me. Runs way cooler than before.

cheers, DL

The hotter your exhaust and turbine run, they more efficient they run and the less backpressure they impose on your engine.
There is no reason to feed cooling air onto them, if you want to keep other parts of the engine bay cooler then insulation and radiation sheilds are the answer.

If you don't have a problem with heat, then what problem are you trying to solve?