Reversing the air scoop findings

For those that havn't read my last post I have gone water to air on my 06 4.2tdi. As the scoop is no longer required I have reversed the scoop to see if I can achieve some sort of airflow to get rid of some engine heat. Something like the A9X Torana and Chevy Camero and also of course the old hot rodders favourite raising the bonnet with some wedges to get that airflow effect.



After removing the scoop and rubber surround I find only two of the holes line up and the front of the scoop ( now the rear ie the closet to the windscreen) does not sit pround to the bonnet. At this point in time I figure this doesn't matter much as I am only fart arsing arround to see if the revsal has any effect.


Next I get a piece of paper towel and cut one side into fine pieces and then I stick it over the opening. I now have a birds eye view of what is goin to happen. Start the truck up and low an behold the fine meshed peice of paper towel flicks out to the windscreen. This is of course the engine fan pushing air out the vent. All good so far.


I start moving the truck and the paper towel flicks out a lot quicker lookin good reach 40 k and all of the sudden the paper towel flicks the other way indicating the air is now flowing back into the motor cavity not lookin good. After drivin for a while an reaching speeds of upwards of 80k the air is continueing to flow back into the engine bay this is not what I wanted.

I come back home and move the paper towel further into the scoop cavity figuring the air flow over the scoop might be having an adverse effect on things but alas this achieves nothing.

Have been driving for three days like this and the flow seems to work up to about 40k in speed then all goes to shit with the flow going back into the engine bay once speed goes over the 40k mark. I have noticed though the area in opening of the scoop closet to the guard (about a third of the opening) the flow seems to be comming out towards the screen when doin 80k. Go figure.

So summing up I think there is some benifit in what I wanted to achieve but I was supprised at how much flow was going back into the motor . I think there is enough merit in the idea for me to go ahead and make a proper install drilling some new holes to make it a flush fitting.

Cheers Gary

There is a fair bit of interesting information about forward v reverse facing scoops.

There is a low pressure area on top of the centre of the bonnet and back towards the windscreen. The Nissan forward scoop is proven to be fairly inefficient as its quite low on the bonnet and stuck in the low pressure area, the ARE scoop is the same size but about 50mm taller to catch the overflow of air bouncing off the low pressure area.

Those running a bonnet protector actually make it worse again and this creates an even larger low pressure zone. God help the guys that have fitted their LED light bar on top of the top bar of their bull bar! They have got no hope!! They are costing themselves H! Decreasing the efficiency of the Scoop and the Intercooler by enormous amounts.

S what you have hit on is the low pressure zone. Upto 40kp/h the rear scoop acts as an exhaust for the engine bay, exit air flow that is being forced through the radiator. Once you hit above that speed the air reverses and the draw from under the car sucks clean air from the radiator and the scoop, either and both should be giving you cooling engine bay temps.

It would be interesting for you to turn the scoop forward with the same tapes and see how much flow goes in there and at what speed. You would be surprised and disappointed I reckon.

I remember reading a fair bit when ARE where first developing their scoop. Plenty of bonnet tests. Postit note tabs folded to stand straight up would also work very well

Also interesting that your bonnet has the centre bulge lifting the scoop high from the start.

Quote:

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Originally Posted by MudRunnerTD

It would be interesting for you to turn the scoop forward with the same tapes and see how much flow goes in there and at what speed. You would be surprised and disappointed I reckon.

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Your not wrong mate. I've noticed on mine with a factory scoop if there is water on the bonnet it does matter what speed I'm doing the drops of water never run back towards the scoop and at some speeds you can watch the water actually run towards the front of the bonnet away from the scoop. I've got a bonnet protecter I've never tried it without that on there might give that a go and see if it makes a difference.

not to be a party pooper but pretty sure you're not allowed to have scoops facing the rear.
point being if you split a hose etc it will cover your windscreen and impair your vision.
Happy to be wrong ,but that's my take on it

If you have a bulbar fitted chances are your scoop isn't working very well if at all
blue tack cotton on the bonnet you'll see what I mean.

They say a STD scoop will not work till 85kph the larger ARE scoop works at lower speeds they say 65kph
plus they have vanes directing air to the front of the IC

Here's some more variables to add to your tests:

Underbody armour
Whether the rubber flaps between the engine bay and wheel arch are installed.

I think you should be happy with the results as it proves the original theory of the reversed scoop

get one like winnie! that thing looks boss!

These good ol boys proved it years ago , Attachment 47480

The air rushing under the car possibly creates a vacuum under bonnet you should put an air temp probe under and measure how hot it's getting, could you also decrease the efficiency of your radiator by allowing another open air path? The vacuum could be forcing more air through radiator !

Went for a spin on the h'way today doin 100k the tapes were really blowin back into the engine bay. I suppose this isn't a bad thing as the modified inlet manifold sits squarely in the middle of the scoop so air must be flowin over it.

When I went to work this arvo I parked the truck where a breeze was blowin directly into the front of the truck and I happened to notice the tapes were moving without the motor goin.

Hey Threedogs not to concerned about legalities the A9X tranny had the scoop as standard and besides the scoop on the truck is hardly noticable it seems to blend in with the bonnet.

So all in all I think I am on a winner and will make it a permanent mod on the weekend.

Just a point of interest on this issue, the afore mentioned reverse scoop on an old torana is to allow air into the engine. At the bottom of the windscreen is a high pressure area at speed which actually forces air back into the scoop to the air filter. I guess this was a result of testing back in the day and also would reduce drag having the scoop facing forwards. The smaller scoops on falcons would work but the huge one on a torana would be overkill facing forwards.
I'm no expert just passing on what others have learned in the past...