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Old 3rd October 2002, 09:45 AM   #101 (permalink)
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Tangent warning!!!!!!

Haven't done more artz, been doing CV, injectors and all sorts.

Don't concern yourself with wheels, procession effects and so on, they will lead you astray!

Paul
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Old 4th October 2002, 07:37 AM   #102 (permalink)
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hey guys has any one got the target rear bumper for there gtr33 it looks to be really well sorted and has the under belly to so it stops drag vacume under rear of the car . i can replicate this for "club members " under special arrangement pm me for details if interested
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Old 14th October 2002, 06:02 PM   #103 (permalink)
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Re: Errrrrrr

Quote:
Originally posted by TOKYO


Anyone seen the DVD yet ?

glen
i have the DVD,its good, worth buying.seems really professional
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Old 17th November 2002, 10:12 PM   #104 (permalink)
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To continue this as promised earlier this week.

We must start now to look at how we get the 'anti-lift' effect we are trying for, the idea is simple if the air under the car can pass the length of the car more quickly and in sufficient quantity than the air that strikes the upper surfaces then we gain a down force, the things that mitigate against this are of course that it is a confined space this can pressurise the air and cause the car to behave like a poor immitation of a Hovercraft to this end the whole design must be based on smoothness of flow, the flow can travel faster but it is NOT the most important feature.

The car is passing thru the air and the air is reluctant to move, so it is pushed aside, over or under its surfaces, if the air can get under the car but has difficulties in passing to the rear of the car then she is gonna lift, the front end is gonna get light and the steering vague.

For a road car the 'venturi' effect is what we have to use, (I hate the venturi word but we are stuck with it I prefer Separate Sides Flow) so the 'cavern' type front end is OK on the standard front end but is in every way wrong for any car trying to promote a negative pressure zone under the car by splitting the air on the front of the car. The use of an FMIC does complicate this situation somewhat as using an SSF design will lessen the efficiency of it unless a small transome wing is used at its base, this is simply a section of bodywork that 'dedicates' air to the FMIC, it HAS to be in projection stuck out as far as it is off the road, this explains the rather 'Jimmy Hill' chin look that you see around the pit lane.

I will this week do some more photoshop stuff (as we all need a good laugh) to describe what exactly I mean.
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Old 28th November 2002, 10:39 PM   #105 (permalink)
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I'm back from the Abyss and in a new job. One that has minimal boredom, hence no web surfing!

I look forward to more of your PS skillz Mycroft!

Paul
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Old 4th December 2002, 12:40 AM   #106 (permalink)
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Iain,

Contemplating cutting some vents in my rear bumper to release some of that air...Do you think it would be worthwhile and if so, what sort of configuration, area, etc. would be most effective?

Peter.
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Old 16th December 2002, 09:30 AM   #107 (permalink)
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Thumbs up Peter, got it.

First, peter the drawings, best efforts have failed so explanation will have to do.
SMIC vent, it is the 'exit' cross-sectional area and its location that makes all the difference, do not put the holes on the outer edge of the car, cunningly arrange for them to vent into the space behind the road wheel, imagine the inner surface as a shell and that you want the SMIC air to follow the surface of that shell as much as possible, you do not want it spilling onto the road wheel or worse still trying to compete with the high pressure air streaming off the front valance just in front of the road wheel.

To put this in perspective, if we give just drilling holes to vent directly onto the tyre (as you have done) an efficincy rating of 100; venting the air to the outside at the roadwheel probably gets 90-95; arranging the air to be taken under the car, i.e. behind the road wheel, will be at least 125 or if you are smart 140-150, the latter equates to a 14% improvement in direct terms.

for your car you would see probably a real 20-30% improvement as at present you have the vents in the wrong place, incorrectly 'directed' and are insufficient in number/area to do the job properly.

Rear diffuser, which is where this thread started prior to being moved for me by Glen. (good man that he is)

We are getting ahead of our selves a little but as I have an hour this morning before my meeting I will just give this a little bit of an airing...

The principle of getting that air from the underside of the car asap is to be followed right up to the rear axle line, after that things change.

Look at your cars rear, notice that the rear end seems to 'tilt upwards' from behind the rear wheels, there is a damned good reason for this, up to this point the air has been confined and has been given an un-impeded passage under the car.

The lift at the rear is to allow as much'space' for the faster air underneath to reform with its surroundings.
T o explain better; Imagine 2 particles of air, as the speeding car approaches one travels under the car the other over it, just putting a tape measure on the that shows one particle has further to travel than the other.

In the past (before 'Aerodynamics') it is this and the weight alone kept Cortinas' and their like on the road at a heady 90mph, it only takes a little bit of differential between the 2 surfaces to produce this simple downthrust. bump up the speeds and the amount of difference must increase and not be compromised.
By 110mph a MKI Cortina is all out of aerodynamics and the cars' a liability.

Iin its journey over the car one of our particles has many temptations before it, these temptations are bad for us the driver, first the Windscreen, it could just squirm round the sidesand try to slip under the car into that lovely free-flowing low pressure zone, it couldflow onto the roof and then succumb to the negative pressure zones on the flanks of the car again in a quest to join the easier passaged particles under the car.

In the 30's there was a fine move toward aerodynamics, mostly inspired by one Dr. Kamm, his work ws ground-breaking, he inspired car designs even after his death.

To our modern eye he appears as mad as Liver and Bacon flavoured Ice Cream, but he was smarter than all his contemporaries, his own 'Dan Dare on Acid' designs can be a bit startling but he was the best ever, from the Bugatti T55 to the Citroen DS19 of 1955 to the Ferrari Daytona in the 70's all have Dr. Kamm to thank for their creation all 3 were ground breaking cars.

So my next statement is probably the greatest dis-service to the man he has ever suffered;
'The answer to good flow is to have all the flows over and under the car rejoin each other with the minimum of fuss or effort.'

That is why we call the rear end design of modern cars the 'diffuser' it does exactly that and that alone is the purpose of the 'tail-up' rear we see on our cars, although Dr. Kamm is best known for the 'Kamm Tail' he did lots of work on the diffuser tail also and it is his design that most modern cars copy.

So, Peter to answer your question; cut 3 big holes in the rear valance put some mesh over them and then see how she feels, it will make the car handle better, but wait for the next 'instalment' as I will post a link to my web page which will in a day or so have some designs for you to look at.

Any questions?
M.
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Old 13th January 2003, 04:45 PM   #108 (permalink)
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Sorry Iain, I never got round to thanking you for the above.

With regard to the oil cooler outlet, are you saying that the hot air should exit behind the wheel, i.e. against the general air flow around the car? If so, there isn't a route for it to be ducted there I'm afraid.

With regard to the holes in the rear valance, I do want to do this but as it's a once only shot, I need to get it right first time. I would be really interested in seeing the designs you refer to in your last post. If having the car physically in front of you would help, I'll gladly bring her up to you.

Peter.
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Old 13th January 2003, 06:41 PM   #109 (permalink)
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No problem matey.
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Old 13th January 2003, 07:49 PM   #110 (permalink)
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And....
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Old 13th January 2003, 07:52 PM   #111 (permalink)
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Mycroft,

I once took Booty to The Fat Duck restaurant in Bray. They had Egg and Bacon flavour ice-cream. Just thought you'd like to know

John
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Old 13th January 2003, 08:21 PM   #112 (permalink)
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You Skyline people certainly know how to live....

Peter I could draw this in 3 seconds but as far as explaining it I'm ****ed at the moment!
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Old 14th January 2003, 12:48 AM   #113 (permalink)
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Something like this Iain?
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Old 14th January 2003, 01:34 AM   #114 (permalink)
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Ever since I mentioned you car looked slightly Pink, the pictures of your Skyline have just got redder and redder, how damned red is that!

Any-road-up, dont cut out shapes like that, round only is the order of the day.

I keep forgetting Skylines have a big single exhaust.

The centre one won't work because I think the Number plate lights are in that location.

If it were my car and I wanted to do this I would line up 4 holes that were the same diameter as the 4 red reflectors in the main lamps and the 'alignment line' would be the shut line for the boot adjacent to the lights. If you look at your reversing light on the left you can see that the shallow sides are slanted, they form a parallelogram, those shallow side provide the styling cue for the rear of the car, making the pair of holes on each side follow this 'cue' down to the crease in the ABS bumper, along those 4 lines (2 each side) I would place them, drilled out and then filled with a medium mesh (20% loss) painted the red of the car.

I am going to take that image and have a go on photoshop, so you can laugh heartily at me.
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Old 14th January 2003, 02:06 AM   #115 (permalink)
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Old 14th January 2003, 08:40 AM   #116 (permalink)
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Cheers Iain, very nice holes, sympathetic too. Will get my rusty pad saw out at the weekend and the chicken wire....
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Old 15th January 2003, 02:43 PM   #117 (permalink)
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Anybody cut a hole in their rear bumper? Just wondering what would be best? Whether to go high speed (router or similar) although this may cause the bumper to melt as it's cutting or low speed/manual, needs to be neat obviously...

Ta.

PS, Iain, the big single has been replaced with a medium twin since that photo...
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Old 15th January 2003, 03:01 PM   #118 (permalink)
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Peter,

Wouldn't you be better off putting in an under tray rather than ruining a rather expensive bit of bodywork ??

looks like an expensive one if it goes wrong !!

good luck.

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Old 15th January 2003, 03:07 PM   #119 (permalink)
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Good point Steve although I would guess making up an undertray to fit tight would be a bit of nightmare plus I quite fancy the holes if I can do it properly...

Iain???
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Old 15th January 2003, 03:26 PM   #120 (permalink)
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ABS requires a pilot hole drilled with an HSS drill bit, turning at high speed.

The radial dial cutter is again an HSS unit.

I have lots of spare parts for Soarers, so I have no fear in drilling holes and trying things......so.....before striking out on what could be a trek into a veil of tears......think long and hard...... go buy some sticky paper cut out circles stick them on this is the sort of I have done before now and thank God I have.

Steve Cs' caution echos my own....do not cut anything till you have the size, location and balls to do it.

I had my car in the garage my drill on a stand a laser to align her and weights to level her then and only then did I start cutting, this is not a 'driveway on a clod blustery day, the ABS must not be worked below 10C as it is brittle at low temps, the drill has to quite beefy and fast.

Caution is required and forward planning.
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