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PostPosted: Tue May 10, 2016 7:13 pm 
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Autospeed has quite a bit on analysing aerodynamics, there's an article about sighting vents etc for intercoolers and cold air intakes, I can't find it at the moment but here's some stuff on wool tuft testing. I'll keep looking for the article I'm after...

Aero Testing 1
Aero Testing 2
Aero Testing 3
Aero Testing 4
Aero Testing 5

Air intake restriction testing

digital manometer (measures air pressure not testosterone / grunting :P )

Got it:
Undertrays, Spoilers & Bonnet Vents, Part 1
Undertrays, Spoilers & Bonnet Vents, Part 2
Undertrays, Spoilers & Bonnet Vents, Part 3

There's a lot more aero stuff on there, it seems to be one of the author's favourite topics, he's also written a book about it...

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PostPosted: Wed May 11, 2016 6:01 pm 
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Image

Maybe this will work (it does !!!)..... illustrates difference between pressure and flow. The A9X scoop feeds the carbs and you can bet Holden knew what they were doing.....

Cheers, Ian


Last edited by 1071 S on Wed May 11, 2016 6:28 pm, edited 1 time in total.

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PostPosted: Wed May 11, 2016 6:27 pm 
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Why an IDA won't fit under the bonnet....

Image


And with the bonnet scoop in place

Image

I can assure you... air flows In at speed ..not VV

Cheers, Ian


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PostPosted: Wed May 11, 2016 8:37 pm 
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1071 S wrote:
Maybe this will work (it does !!!)..... illustrates difference between pressure and flow. The A9X scoop feeds the carbs and you can bet Holden knew what they were doing.....


You don't have the rest of the aero article do you?

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PostPosted: Wed May 11, 2016 11:00 pm 
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Yes, I'll find you a link.

Cheers, Ian


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PostPosted: Wed May 11, 2016 11:36 pm 
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I'm going to have to pull my BE (Aero) out here and agree that the bottom of the windscreen is a HIGH pressure area. But why would you believe me just because i read a few books, did a bunch of experiments, another bunch of assignments, and passed some exams?

How we can prove it is high pressure scientifically is not with tape or tufts, that will only tell you direction of flow if there is any and if it is turbulent or laminar flow. It is not a measure of pressure.

To measure pressure you need to build yourself a U-tube manometer, which is a device for measuring relative pressures. Graham will be familiar with the calibrated manometer that he uses for flow testing heads, but this is a little less than mobile because it is designed for a specific purpose and mounted to the bench.

The simplest way to build one is to get some clear plastic tubing long enough to reach from inside the cabin to the area you want to measure relative pressure and tape/clip/glue it in a U shape to a piece of white board that you can mount in the cabin, or have your assistant hold. Fill the tube with just enough water, mixed with food colouring to make it easier to see against the board, so that you can mark the movement of the water one way or the other on the board. Each end of the tube can now be taped to the position you want to take relative measurements of. I would recommend one end remain in the cabin and the other be moved at various points. Get your assisitant to take pics and log the positions while you drive at a steady speed that is the same for all measurements. To save time, build lots of parallel U-tubes and tape the measurement ends at the various points.

If you want to remove any measurement bias that may be caused by the direction that the end of the tube is pointing, then repeat each measurement a number of times with that end in various directions, documenting each time. If you want to measure relative to the free stream pressure instead of cabin pressure, you will need to put the end of the tube(s) parellel to the airflow far enough outside the body of the car that it is not affected by the boundary layer.

Image

By comparing how high or low the water moves in the tube when measuring the different points you will build a relative pressure map that will confirm what is what. It will look remarkably like that picture from the MTN.

I have been here before, check out Ben's effort to work out the best plase to put vents on racing Soarers http://soarercentral.com/sc-forum/messages/263854/341853.html.

Anyone want to take up the challenge?

I would also be interested if anyone has compared an engine bay pressure map with side mount radiator (with and without cowling, rubber shroud seal etc) to a front mounted radiator (with and without the rest of the grill blanked off), especially the pressure drop across the radiator in each case. If there is no pressure drop across the radiator, then air is not going to flow through it very efficiently, hence poor cooling.

If only i had the time . . .

cheers
michael

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PostPosted: Fri May 13, 2016 12:06 pm 
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So this is why we have such problems cooling the mini engines once they get more performance, as the diagram shows high pressure under the bonnet and under the guards. So ideally we need to create a low pressure zone behind the rad in the offside guard near the radiator for better cooling... interesting.
It would also be interesting to see if those minis out there with a air dam / splitter from wheel arch to wheel arch cool better than those with out? Food for thought.

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PostPosted: Sun May 15, 2016 10:11 am 
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Torana XU1 flutes in the side of the guards??? that should work right?? :D

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Last edited by Freddo on Sun May 15, 2016 2:59 pm, edited 1 time in total.

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PostPosted: Sun May 15, 2016 11:15 am 
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1071 S wrote:
Yes, I'll find you a link.
Cheers, Ian


Any luck? I'd still be really interested to read it as apart from removing the seams I haven't seen a lot about minis and aerodynamics.

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PostPosted: Sun May 15, 2016 5:32 pm 
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fuzzy-hair-man wrote:
minis and aerodynamics.


oxford dictionary wrote:

oxymoron

A figure of speech in which apparently contradictory terms appear in conjunction


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PostPosted: Sun May 15, 2016 5:39 pm 
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Hi Michael
I don't have one of those BE or PD or an XYZ i'm just one of those fitter and turners from the 60's and I did pass as well as heat treatment, welding etc, but I didn't go to Uni, I do read books but I don't always believe what I read and when I don't I go and test for my self.
So to prove what happens with air pressure at the bottom of the windscreen I took my manometer from my flow bench and hooked it up to my BT50 Mazda truck which has a better aero shape than a mini,and it was very interesting at 50 to 90 kilometres with the pick up at the bottom of windscreen it never went above 1in but when I put it at the front of the bonnet the faster I went the higher the reading 2 1/2 ins, so I have left it all hooked up and if you want to come and have a look for your self you are more than welcome but please bring your Mini so we can hook it up to it.
My mini isn't going at the moment but when I get it going I will test it for you.
Now as I said in my earlier post the modern cars of to day with their slope back windscreens may give a different reading I will try it on my car later to see what the difference is,so I will still stick to what I said and maintain that the bottom of the Mini windscreen is a low pressure area, this is why David Visard did not have to run an air cleaner on his Mini with the IDA carbie.
Graham Russell

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PostPosted: Sun May 15, 2016 7:38 pm 
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http://www.theminiforum.co.uk/forums/to ... -the-mini/


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PostPosted: Sun May 15, 2016 8:01 pm 
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I finally read the articles I linked above again (rather than skimming to find the link) the "Undertrays, Spoiler & Bonnet Vents, Part 3" one is the most relevant here's an image and quote:
Image
Quote:
This DaimlerChrysler graphic shows the typical frontal pressure distribution of a car. Looking just at the bonnet you can see that there is low pressure (blue) where the air wraps around the leading edge of the bonnet, grading to high pressure (green) as the air reaches the obstruction which is the windscreen.

So you wouldn’t site a bonnet outlet vent close to the windscreen – in fact that’s usually where the cabin ventilation inlet ducts are... they’re taking advantage of that high pressure! Looking at just the exterior pressures, what we want at the vent location is the very lowest external pressure.

That’s the theory – but what about on the road? By using the Magnehelic gauge (see the previous parts in this series for more on these gauges), it’s dead-easy to directly measure the pressures over the outside of the bonnet. Simple run a tube from the Magnehelic gauge to the area to be measured, making sure that the open end of the tube is at right-angles to the direction of airflow. Leave the other port of the gauge open, and swap the tube from port to port, depending on whether you find that you’re measuring a high or low pressure.

This is exactly what we did on the Maxima, using the same 80 km/h road speed for all testing. The results were astounding – not because they reflected the textbook example shown in the graphic above, but because the pressure variations were so great! As can be seen here, the front half of the bonnet surface was clearly a negative pressure zone, while the rear half was all in positive pressure. And the further forwards the measurements were taken, the lower the pressure; and the further backwards, the higher the pressures!

But as the author finds out earlier in the series it doesn't always follow the theory... so as GR said there's no alternative to doing the testing yourself, it seems the mini's requirements aren't the usual as we'd like to promote higher under bonnet pressures to promote airflow through the radiator and/or lower pressure in the guard. I can't remember the source but AFAIK the guards or wheelwells are generally a low pressure area. I figure the mini is different enough to upset a few of the theories.

Thinking of trying an undertray/sumpguard which unlike the author's (Part 2) would aim to seal off the under bonnet area and raise the under bonnet pressure.

Thanks 69k1100, gonna go read it now :D

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PostPosted: Sun May 15, 2016 8:38 pm 
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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

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PostPosted: Sun May 15, 2016 8:49 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

So should I leave the rust holes in my A panel? :P


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