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Old 07-31-2007, 03:51 PM   #21
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I hit the aerodynamic jackpot

I hit the aerodynamic jackpot:
http://www.mayfco.com/tbls.htm
it lists the 95 metro lsi as a cd of 0.340 and an area of 20.00 sqft for a cda of 6.80
and the spitfire as 0.420, 15.47, 6.50

Here is a whole page on determining your cd (and I would think crr could be approximated as a low speed test 5mph to 0 or so).
http://www.mayfco.com/cdmodel.htm


check it all out:
http://www.mayfco.com/analyses.htm

But I still couldn't see humping a working metro into a spitfire. Chop top has got to be way easier than making a front wheel drive spitfire. You'd have to be really bored to do that
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Old 07-31-2007, 03:57 PM   #22
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Quote:
Originally Posted by skewbe View Post
Ahh, you are hoping to avoid doing body chopping? a-la:


Well that's simpler, I think the metro has something like a .32 (unconfirmed) coefficient of drag and the spitfire has a .42 (per wikipedia). unless the frontal area of the spitfire is porportionally less, the geo will have less drag.

If both cars are running, you can compute the CdA for each with a series of coastdown tests and determine it that way.

http://www.gassavers.org/showthread.php?t=4419&p=64771
I always thought it would be interesting to do the chop like above where the entire passenger side is removed, and then do the "Dave Cloud" chop like listed in the original post to the driver's. Kind of a combination to maximize it. Of course it would be a 1 seater though, but I'm sure that wouldn't bother some of us on here, or atleast me.

I think it would also be very cool if on the driver side, the front window pillars were lowered too...to have even a sleeker profile. That would have to be estimated to the height of the driver though, but I'm 6' and I think it could be lowered about 2 inches in my `95 before it would touch my head...
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Old 07-31-2007, 04:45 PM   #23
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The Triumph will be a much cooler vehicle to drive but will be less practical and much more work. I'd go for the Triumph if you have time.

I used to have an MG-A in the early 70s. Beautiful British Racing Green with spoke wheels. Would have loved to have had a modern reliable engine, transmission, suspension, electrical system, etc., in it. It was really a terrible car.

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Old 07-31-2007, 08:31 PM   #24
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Personally, I think if the triumph were resurrected into a more "useable" car, it would show people what can be done to recycle older cars instead of just junking them. :-)

You could also try a mazda rotary or a motorcycle engine if you wanted to save weight... :-)
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Old 07-31-2007, 09:03 PM   #25
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FYI, a couple of electrified spitfires (= cool):
http://www.youtube.com/watch?v=9vhywPK7Vz0
http://www.rtpnet.org/teaa/newslette...ews-10-01.html
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Old 08-01-2007, 02:39 AM   #26
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Quote:
Originally Posted by skewbe View Post
I hit the aerodynamic jackpot:
http://www.mayfco.com/tbls.htm
Yup, seen this info before.

You did see the disclaimer at the top: "The charts shown below are a product of my imagination, but are developed from data contained in car design text, aeronautical text and just plain guess work."

Unfortunately, he doesn't indicate which figures fall in what category
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Old 08-01-2007, 05:41 AM   #27
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yes, the verbiage there is a little slippery. The actual cD and area values were from a DOS program called cartest. Some of the frontal areas were not listed and he guessed at those. I ran the program and saw that the 1995 metro was listed, but the 92 metro and the 1980 spitfire were not.

I also noted that the metro only gets .75 G in the skidpad according to cartest I've been planning on talking to the guys on teamswift about better cornering, but now I know why. (the spitfire isn't any better)


So push that spitfire up to 60 with another vehicle and let it coast, and see what happens

I have actually conceived of a way to determine frontal area (probably been done before):
1. take a picture of your car from the very front, halfway up it's height from as far away and with as much zoom as you have (not digital) so that it fills the frame but you can still see the outline. Use a contrasting background if possible.
2. measure the width of the license plate
3. use image software and figure out how many pixels wide the license plate is.
4. use the image software to outline the car, make the car entirely black and everything else white. Save it into an easy to parse file format (i.e. 256 color uncompressed bmp).
5. slap a program together to count the number of black dots in the black and white image file. (note, some image software may be able to tell you the area selected in pixels)
6. multiply that number by the pixels per inch (license plate width pixels/actual width).

And Bob's yer uncle.
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Old 08-01-2007, 08:22 AM   #28
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Don't push a Spitfire- you'll crush it!
Not if you push it with a Geo.

Anyway, that aero site was an interesting exercise in mental masturbation for its owner, though it did have a lot of very useful info and formulae. At least the guy issued a disclaimer.

Did anyone else notice that the "cd x ft2" figure was lower on the Triumph than the Geo?

Without a wind tunnel everything is guesswork, but I'd settle for an educated guess. Even I'm smart enough to know that if your frontal area is slightly off or if you're using an inaccurate published Cd figure you could make a Ferrari look like a barn door.

Back to the drawing board. And the want ads.
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Old 08-01-2007, 08:28 AM   #29
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...Without a wind tunnel everything is guesswork ...
If you perform proper coastdown testing, you will not be guessing.
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Old 08-01-2007, 09:14 AM   #30
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I got the Triumph at an estate sale. It's not currently registered because it narrowly failed the smog check on the first go-round. The temporary permit expired a few days ago so coastdown is not an option. I'd have to tweak the stock motor, get it tested again and risk having the thing declared a "gross polluter", which is a real PITA in Cali. The cars barely met U.S. emission standards when they were new and had to be detuned to the point that no one would buy them anymore.

Anyone who maintains a late model Spit with a stock motor in this state is doing it out of love. The other day I decided I wasn't really THAT much in love.

This really sucks because the motor is tight and the car only has 39,000 original miles on it.














Anyway coastdown isn't currently an option.
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