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Old 12-06-2009, 11:23 PM   #31 (permalink)
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Quote:
Originally Posted by roverdriver View Post
That kind of increase in speed could not be created purely from improved aerodynamics- don't forget that streamlining only helps after about 60 mph anyway.
It's a common misconception that aero drag becomes an issue only at highway speeds and above.

Have a look at this tool: Aerodynamic & rolling resistance, power & MPG calculator - EcoModder.com

The default numbers provided are for my vehicle in stock form, and with its drag area (CdA - product of frontal area and Cd), it shows that over half the power required to go just 30 mph is spent overcoming aerodynamic drag. And this is for a modern vehicle with a dramatically lower (ie. better) CdA figure than a Model T.

It also happens to show that 13.8 kw / 18.6 hp are required to get a vehicle with its rolling & aero resistance figures to 70 mph.

So a sufficiently streamlined car with a 22 hp engine could do it.

I suspect you may have the figures for the T at your fingertips, which you can input into that tool. You could even work the figures backward to find out just what change in CdA is needed to get to 70 mph from the stock starting point.

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Old 12-06-2009, 11:42 PM   #32 (permalink)
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Very interesting link, Metro. Thank you. Unfortunately things like drag coefficients were not priority figures for cars in 1927, so I don't have suitable information to be able to use the site, however from a cursory study of the table, it does seem theoretically possible to achieve 70 mph from 22 hp, (Is that rated hp or brake hp?) but the streamlining would need to be highly efficient, the engine extremely efficient, and all sources of friction minimised.

The streamlining of the modified car in this thread could in no way be described as highly efficient, and the story says that it performed on the original engine. Cast iron pistons and a compression ratio of less than 5:1 are not conducive to propulsion at 70 mph.

As I said before, the Chev gearbox as an overdrive could help achieve a high speed, but the same can be achieved with engine modifications.

I would have loved an opportunity to study that car and see what else he did to it.
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Old 12-07-2009, 02:35 AM   #33 (permalink)
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Quote:
Standard final is 11/40. Options are 10/40, 12/39, and 13/39
...or 3.64:1, 4:1, 3.25:1, and 3:1.

Under the old tire labelling system, the 30 x 3 rear tires had an O.D. of 30" for a circumference of 94.2". With 63360 inches/mile we get 673 revs/mile. At 70 mph the wheels go 785.2 rpm.

So at 70 mph:

With std. axle, engine rpm is 2858 rpm;

4:1 - 3141 rpm
3.25:1 - 2552 rpm
3:1 - 2356 rpm

Now here's a few interesting tidbits:

Ford Model T Frequently Asked Questions (FAQ) - The Frontenac Motor Company Brass-Era Automobile Collection

They say the tires are inflated to 75 psi!

They also say 25 mpg is dreaming- more like 10-12.

Dah! NOW I find this:

http://www.nwvs.org/Technical/MTFCA/...orqueSpeed.pdf

and if I'm understanding it right, redline should be considered at about 1600 rpm. Another source says so too: http://www.popularmechanics.com/auto...46.html?page=6

So without special gears and/or engine mods, 70 mph does seem highly unlikely.

Although with some W.A.G.ing, the EM performance calculator says it should be just able to hit 70 with 20HP!

http://ecomodder.com/forum/tool-aero-rolling-resistance.php?Weight=1460&WeightUnits=lbs&CRR=.00 8&Cd=.34&FrontalArea=22&FrontalAreaUnits=ft^2&Fuel Wh=33557&IceEfficiency=.18&DrivetrainEfficiency=.9 5&ParasiticOverhead=0&rho=1.22&FromToStep=5-120-5

No, I don't have the permalink thing figured out.
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Old 12-07-2009, 02:45 AM   #34 (permalink)
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Good information, Frank.

Tyre psi is correct for beaded edge tyres. I used to put between 70 and 80 psi into them.

Yes, the T has a slow revving engine. Fit aluminium pistons and that makes quite a difference and the crankshaft handles the extra rpm o.k. OHV kit boosts power and rpm even further so 3,000 is quite possible.

I agree with the lower mpg. I managed a max of close to 25, but that was a long run on level roads. I usually planned on 10 to 15 mpg, remembering that the tank holds only 8 imperial gallons ( 10 us), so would fill up, or at least top off after about 70 miles, just to be sure.
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Old 12-07-2009, 02:50 AM   #35 (permalink)
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Old 12-07-2009, 03:41 AM   #36 (permalink)
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That's right Frank. Sort of makes one wonder why modern cars need all of that junk on board.

I am a great believer in a basic motor car. Unfortunately don't have a T anymore, nor my beloved Model A. Compared to them the 1955 Rover, which is my everyday transport is quite modern, but at least it still has a carburetor and distributor, manual gearbox and anything that needs attention can be repaired rather than having to be replaced.
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Old 12-07-2009, 10:43 AM   #37 (permalink)
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Hi roverdriver...

Quote:
Originally Posted by roverdriver View Post
it does seem theoretically possible to achieve 70 mph from 22 hp, (Is that rated hp or brake hp?)
That's road horsepower - power at the drive wheels.

Quote:
The streamlining of the modified car in this thread could in no way be described as highly efficient,
I disagree. The shape of the car is pretty optimal - focus your attention on the rear, where the majority of drag reduction is achieved, and he's got it right. He also significantly reduced frontal area.

The big question mark is the impact of the exposed suspension/wheels on Cd.

A quick search uncovered a source (quality unknown, but the figure is consistent with others I've seen for this style of car) that estimates the Cd at 0.80 and frontal area at 25 sq. ft. for a "roadster" style T.

Plug those numbers into the tool and you see a couple of interesting things: the speed at which half the power is being "spent" on aerodynamic drag is 20 mph.

Halve the Cd figure, reduce A by a reasonable amount (as he did), reduce the engine efficiency value for an old tech, low compression motor, and it's still within the realm of possibility to approach 70 mph with the power it had.

Quote:
I would have loved an opportunity to study that car and see what else he did to it.
Agreed. It's too bad it met its fate at a railway crossing.
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Old 12-07-2009, 06:55 PM   #38 (permalink)
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Old 06-18-2010, 06:25 AM   #39 (permalink)
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wow this is amazing i llove it simply perfect
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Old 05-28-2012, 09:26 PM   #40 (permalink)
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Taking a break from Memorial Day cleaning (fun!), and came across this old thread. Wanted to bring it to people's attention, since nobody has commented in two years. I use one of these images on a poster board explaining the principles, culture, and history of modding. (Click to the OP.)

[EDIT: btw, what happened to this car, Metro?]

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