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PostPosted: Fri May 06, 2016 8:11 am 
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Hi guys,

Anyone using a downdraft weber, and been able to get it under their bonnet with an air cleaner? - and without modding the bonnet itself?

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PostPosted: Fri May 06, 2016 6:30 pm 
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Didn't GR specify a low profile air cleaner that he said fitted ok?

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PostPosted: Sat May 07, 2016 11:56 am 
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slide wrote:
Didn't GR specify a low profile air cleaner that he said fitted ok?


Last I heard he was on the hunt for one? Do you have the details?

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PostPosted: Sat May 07, 2016 1:47 pm 
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There is not much height there, even less with a 1275 block.
I would put an A9X (backwards style) scoop on the bonnet. Then fit a Ramflo with Unifilter foam.

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PostPosted: Sun May 08, 2016 12:25 pm 
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Will this fit under the bonnet? It is claimed to be only 1 3/4 inch high

http://www.carburetion.com/Products/Pro ... =CUBidf175

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PostPosted: Sun May 08, 2016 7:41 pm 
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"I would put an A9X (backwards style) scoop on the bonnet."
Don't you need that under bonnet air pressure to flow through the radiator?

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PostPosted: Sun May 08, 2016 10:27 pm 
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TK wrote:
"I would put an A9X (backwards style) scoop on the bonnet."
Don't you need that under bonnet air pressure to flow through the radiator?


Well it can already flow down the back of the motor and out the bottom, considering the big frontal opening area I don't think it will make any difference.
Vizard ran a 48IDA with the trumpets through a hole in the bonnet...

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PostPosted: Mon May 09, 2016 3:09 pm 
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No, it doesn't make any difference whether you run small holes for sock type filters or a big one for a K&N...

Cheers, Ian


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PostPosted: Mon May 09, 2016 4:45 pm 
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drmini in aust wrote:
TK wrote:
"I would put an A9X (backwards style) scoop on the bonnet."
Don't you need that under bonnet air pressure to flow through the radiator?


Well it can already flow down the back of the motor and out the bottom, considering the big frontal opening area I don't think it will make any difference.
Vizard ran a 48IDA with the trumpets through a hole in the bonnet...


a backwards facing scoop takes advantage of the high pressure at the base of the windscreen which pushes air back under the scoop - which is why they did it with the A9X... works really well, and doesn't stir the fuel up like a forward scoop or open trumpets - open trumpets are bad because the fuel gets sucked out of them

a backwards facing scoop and a plate with a seal that the bonnet sits down on would be the best I reckon

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PostPosted: Mon May 09, 2016 5:26 pm 
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that makes sense

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PostPosted: Mon May 09, 2016 6:22 pm 
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Hi Simon
I think you will find that the bottom of the wind screen rear of the bonnet is a low pressure area this is why they face the scoops facing to the rear so the induction can pull from still air, this is why you can run trumpets through the bonnet at the rear with out an air cleaner.
This is why people raise the rear of the bonnet to allow the high pressure air to exit into low pressure area and take the heat with it,Barry Jones and I did testing with our mini's in the 70's by taping bits of string all over the front, roof and side of our car to try and see what the air was doing over the car, we took it in turns at standing at the pit wall at the bottom of the straight at Oran Park, OH and S would love that today the string on the front of the bonnet just went straight back while the string at the bottom of the screen and the rear of the bonnet didn't do much just wriggled around, and that was at around 95 MPH.
Graham Russell

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PostPosted: Mon May 09, 2016 7:16 pm 
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happily corrected :) yet again - but I did get GR to share some wisdom, so I call that a win all round

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PostPosted: Mon May 09, 2016 8:10 pm 
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Don't confuse stagnating high pressure air with low pressure. There is a high pressure zone wherever the air is slowed. This is the factor behind using horizontal front lip extensions on race cars. The air stagnates on the front of the car causing a high pressure zone that then pushes down on the splitter.

If you made a big square board and taped short lengths of string in a grid all over it then pushed it through the air flat on you would see the strings forming a pattern. The ones near the edge would point towards the edge and not flutter much but the ones in the middle would flop around or be virtually still. The highest pressure is in the middle.

One of the most common mods to an mx5 is to run the inlet from the vented area at the base of the windscreen.

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PostPosted: Mon May 09, 2016 11:09 pm 
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The reason the cabin air vents are also located at the bottom of the front windscreen are to take advantage of the high pressure zone providing positive flow into the cabin.

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PostPosted: Tue May 10, 2016 5:49 pm 
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Hi Tim 1
Please tell where else you could put a fresh air duct in the front of a car with out getting full of water? at least at the bottom of the windscreen there is a drain which is lower than the inlet for the air.
Have a look at some wind tunnel testing with passenger vehicles an note how the air flows over the body, but in saying that modern cars with there layed back windscreens they are getting much better flow across the body.
Any one who has been to my factory may have seen the photo on the wall of Darren Burns mini at Eastern Creek doing around 100 MPH in very , very heavy rain the rain is leaving the bonnet hitting the windscreen about half way up then leaving the top of the screen and going over the roof at about 60 deg and not touching the roof at all,an excellent photo of air flow over the mini showing why they have no top speed compared to other cars of simular capacity.
Try this like we did, take a piece of pipe about 2ins in dia tape it to the front of your bonnet facing forward , then take another piece the same length and tape it in front of the windscreen facing forward and feel the difference and let it blow into the car, we used that black pipe you can get from Bunnings,i still say the bottom of the windscreen is lower pressure.
Graham Russell

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