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PostPosted: Sun May 15, 2016 8:54 pm 
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Oh dear, worry, worry...

Joined: Fri Jun 19, 2009 5:31 pm
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Location: North Rocks
Hi gtogreen1969
No, cut the rust out nice and neat and leave the hole there :D
Graham Russell

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PostPosted: Sun May 15, 2016 9:42 pm 
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GR wrote:
Hi Fuzzy-hair-man
I don't know how old you are but back in the 60's (late) my era the mini sports sedan guys were cutting a 2ins hole in the A panel this allowed the air escape from under the guard which improved the cooling, but CAMS stepped in stopped the drilling of holes in the body, but that really helped.
Graham Russell


Thanks, a little before my era, I was just wondering if it would be possible to (or if those holes) use the mini's seams on the A panel to our advantage, there 'should' be a small area of low pressure behind the seam, a louvre(s) cut behind the seam might make use of this low pressure area to suck hot air out of the guard it might even help drag???!!

My mini is a road car so I'm trying to keep it low key, but it's great to get a better understanding of what's going on and what actually works rather than ideas and theory running round in my head.

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PostPosted: Mon May 16, 2016 3:50 pm 
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Hope these work....

Cheers, Ian


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PostPosted: Mon May 16, 2016 6:56 pm 
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Thanks Ian! interesting read.

The following seems relevant (from http://www.carbonweezel.co.uk/testing/testing_mini.html#boards):
Quote:
Bonnet
The flow at the base of the windscreen is actually reversed, so the racer's trick of raising the rear lip of the bonnet to allow hot air to escape looks like a waste of time. It also caused a further small increase in front lift too.

Image

Heavier particles (ie dust) in an airflow should find it harder to make the turn if airflows are reversed so may contribute to the reason Vizard could run no filter?
Not sure I understand the comment about it being a waste of time for letting hot air escape, if there's higher pressure under the bonnet it may not need an airflow to vent.

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PostPosted: Tue May 17, 2016 11:31 am 
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what a great thread this has turned in to - and it all started when I talked out of my arse and said something about the air pressure of a reverse scoop - win for Simon :D

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PostPosted: Tue May 17, 2016 12:38 pm 
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I used to run my Fiat 124 coupe at hillclimbs and drags with the bonnet packed up 1". But it was just to let heat out and stop vapour lock whilst waiting for the start.

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PostPosted: Sat May 21, 2016 1:14 pm 
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Oh dear, worry, worry...

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HI All
Got my mini going and taped the air tube to the bonnet, fixed it to the back of the bonnet below the windscreen and got no reading at all, fixed it to the middle of the bonnet once again no reading,i then got out of the car blew into the tube and up went the ink so I fitted it to the front of the bonnet about 2ins back and once again no reading, now my mini is a LS so may be the round nose may be different, but it looks like the whole bonnet area is a low pressure area, if some one would like to bring their round nose around I will do the test on a round nose.
The comment about raising the bonnet at the rear being a wast of time in the wind tunnel test may hold true to that car with all the air dams and splitter on the front, but on a normal mini it would have to let the high pressure out from under the bonnet because the base of the windscreen is a low pressure area.
Graham Russell

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PostPosted: Sat May 21, 2016 7:36 pm 
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I can drop down tomorrow arvo GR. Cuppa tea time.

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PostPosted: Sat May 21, 2016 9:32 pm 
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GR wrote:
Got my mini going and taped the air tube to the bonnet, fixed it to the back of the bonnet below the windscreen and got no reading at all, fixed it to the middle of the bonnet once again no reading,i then got out of the car blew into the tube and up went the ink so I fitted it to the front of the bonnet about 2ins back and once again no reading, now my mini is a LS so may be the round nose may be different, but it looks like the whole bonnet area is a low pressure area, if some one would like to bring their round nose around I will do the test on a round nose.


What's the scale on your manometer GR? one of the links above on aerodynamics suggested that a 0 - 1 inch gauge is of most use for aerodynamics, may explain why readings seem to be all or nothing...??

Quote:
(The 3-inch gauge lets you use it in other applications as well – see below. If you intend using it purely for aerodynamic work, buy a 0-1 inch gauge like the one shown here.)


Or is it possible to tilt it a known amount (not sure what your gauge looks like) so you get a finer resolution? guessing here...

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PostPosted: Sun May 22, 2016 7:40 am 
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Oh dear, worry, worry...

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Hi Fuzzy hair man
I have two manometers one goes to 16 ins the other one goes to 54 ins it is used for measuring the air speed in the ports etc.
If you just blow into it with your mouth it will show about 2 1/2 ins it is very sensitive, it works on my BT50 so there is no reason for it not to work on the mini,if you hold it out the window it works, so iwill try it on some other cars.
Graham Russell

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Last edited by GR on Sun May 22, 2016 4:11 pm, edited 1 time in total.

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PostPosted: Sun May 22, 2016 10:03 am 
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Ok thanks, looks like the clubby transitions from the slab front to the bonnet too quickly and makes the whole bonnet area low pressure then.
That's gotta be causing lift then doesn't it?

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PostPosted: Sun May 22, 2016 4:03 pm 
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Oh dear, worry, worry...

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Hi Fuzzy hair man
Aaron came down with his round nose mini and we did some more testing, better pick up, with the pick up at the finish of the round part of the bonnet at about 60k's it was getting up to 1 1/2 going round corners seemed to affect it at the base of the windscreen it was down again varying from 1/2 an ins to 3/4 of an ins.
Taping to the windscreen about 6 ins down from the top was much the same as on the front of the bonnet as was taping it to the roof at the top of the windscreen.
Then we put the pick up under the bonnet over near the clutch at about 45 deg , this sent the pressure up to 1ins but once again it was moving around it may of had something to do with the grill it was one of those wavy ones wether it makes a difference I don't know need more testing.
Not happy with the testing on my LS so I will go back and test that again.
Graham Russell

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PostPosted: Mon May 23, 2016 6:07 pm 
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Great thread.
But how do you go from...How do I fit a carburettor under the hood to the finer points of aerodynamics?
But keep it going 8)


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PostPosted: Mon May 23, 2016 8:50 pm 
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Interesting stuff Graham.

I assume you are taking measurements on the centreline and comparing to static pressure inside the car. Does it make a difference if the windows are open or closed?

There is probably a really big volume of circulating air caused by the edge of the bonnet that does not re-attach to the bonnet before the windscreen on the LS. I expect that on Aaron's roundy that this circulation is smaller.

We know the theory of these circulations and how they re-attach to the bonnet prior to the bottom of the windscreen on a larger car, but the Mini bonnet is so short that it probably has not got the space to do so.

Under bonnet would be very turbulent, so varying pressure is not surprising.

Would be interested in the variations in with speed and going out to the sides as well, but it all takes heaps of time right?

Thanks for having a go at this, I simply don't have the time otherwise i would love to come and have a play too.

cheers
michael

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PostPosted: Tue May 24, 2016 11:59 am 
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GR wrote:
Hi Fuzzy hair man
Aaron came down with his round nose mini and we did some more testing, better pick up, with the pick up at the finish of the round part of the bonnet at about 60k's it was getting up to 1 1/2 going round corners seemed to affect it at the base of the windscreen it was down again varying from 1/2 an ins to 3/4 of an ins.
Taping to the windscreen about 6 ins down from the top was much the same as on the front of the bonnet as was taping it to the roof at the top of the windscreen.
Then we put the pick up under the bonnet over near the clutch at about 45 deg , this sent the pressure up to 1ins but once again it was moving around it may of had something to do with the grill it was one of those wavy ones wether it makes a difference I don't know need more testing.
Not happy with the testing on my LS so I will go back and test that again.
Graham Russell


Thanks GR,
So there seems to be a layer of relatively low pressure air back from the curve on the bonnet, hence the bonnet vents in Fig 5 of '1071 S' article, seems to confirm the image of over bonnet flows.

Which might suggest you could add a scoop etc to the bonnet with only a small impact on aerodynamics... hang on even better...

I wonder what the air flows would look like if you were to raise the rear of the bonnet dramatically like 3 - 4 inches but also make the front curve less sharp,it could even give room for that IDF carb... :D

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