Simviation Forums

Posted: **Mon May 14, 2007 3:04 pm**

*
Prelude: I had a Monte Carlo with a 350 cu. in., 4 bbl. engine which averaged it's best fuel milage at 65 - 70mph. I then had a Monte Carlo with a 400 cu. in., 4 bbl. engine that actually got its best fuel milage at 75 - 80mph (but the speeding tickets would have outdone the fuel savings to continue such management). I also had a truck with the same engine and basic exhaust configuration as the 350 Monte Carlo: only 18mpg.
I know some of you watch Mythbusters; I rarely have but caught a couple of the rerun 2004 shows this past week.

Scenario: One of these shows closed with each of its two costars driving their own SUVs around the track, one with his windows closed and the A/C on full while the other drove his with the window down and the A/C off. Contrary to what computation indicated, the one with the A/C on ran out of fuel first. From all information passed to me in the past, that would be the probable result, anyway.
However, they undefinitively concluded that they'd proven that windows down goes farther than the A/C on approach. Knowing my technicality levels -- that is not what they proved, true or not. Anyone wish to elaborate as to what they did and did not prove with their errant methodology -- or how it was errant?

* Sorry, I made up 'Mythodology' just for the post title.

8-)

Posted: **Mon May 14, 2007 3:07 pm**

Prelude: I had a Monte Carlo with a 350 cu. in., 4 bbl. engine which averaged it's best fuel milage at 65 - 70mph. I then had a Monte Carlo with a 400 cu. in., 4 bbl. engine that actually got its best fuel milage at 75 - 80mph (but the speeding tickets would have outdone the fuel savings to continue such management). I also had a truck with the same engine and basic exhaust configuration as the 350 Monte Carlo: only 18mpg.
I know some of you watch Mythbusters; I rarely have but caught a couple of the rerun 2004 shows this past week.

Scenario: One of these shows closed with each of its two costars driving their own SUVs around the track, one with his windows closed and the A/C on full while the other drove his with the window down and the A/C off. Contrary to what computation indicated, the one with the A/C on ran out of fuel first. From all information passed to me in the past, that would be the probable result, anyway.
However, they concluded that they'd proven that windows down goes farther than A/C on approach. Knowing my at technicality levels -- that is not what they proved, true or not. Anyone wish to elaborate as to what they did and did not prove with their errant methodology?

8-)

I don't usually watch that show but I watched a little bit of that episode you are talking about. I didn't get to finish watching it though. :)

Posted: **Mon May 14, 2007 11:16 pm**

My experiance watching Mythbusters is that if they can't duplicate the conditions of the myth, either through lack of understanding or failure to present proper conditions, then the myth must be busted.

Posted: **Mon May 14, 2007 11:44 pm**

The mythbusters do an awful job of trying to bust myths. Don't get me wrong, I love the show, and I've seen all of them, multiple times, but their engineering is terrible. A good example of this is the "Break-step Bridge" myth, where they tested the myth of an army walking over a bridge sets the bridge into resonance that destroys the bridge. The way they tested it was they put some boots on some pneumatic actuators and set these on a bridge they made out of steel rods and drywall, then turned the actuators on at some random frequency. If you have done any physics, or basic engineering, you've probably learned about natural and resonant frequencies and what effect they have, and watching this particular myth becomes difficult. This is also an example of a myth that they "busted" but has been proven in the real-world (e.g. the Tacoma-Narrows bridge was destroyed through resonance).

As far as driving with your windows down. The rule of thumb is if you drive short distances, at slow speeds, leave the windows down, and if you drive for a long time while going fast, use the air conditioning. That's what I've always heard, and after a couple of classes here, I believe it.

Posted: **Tue May 15, 2007 4:38 pm**

"Mythodology"... nice porte-manteau word, there; Humpty-Dumpty would be pleased.

Posted: **Tue May 15, 2007 8:16 pm**

[quote]The mythbusters do an awful job of trying to bust myths.

Posted: **Tue May 15, 2007 11:11 pm**

Right Chris, I agree. The show is terribly entertaining, it's probably in my top five list of favorite shows, and I wouldn't change the show at all. If all the engineering was done perfectly, it would be a documentary, and it would be horribly boring, but on the other hand, I wouldn't do anything drastic based off of what they find in the show.

And I'll give them credit, there are many times they do have good, elegant ideas, and those are just as entertaining as their spectacular failures.

Posted: **Wed May 16, 2007 5:34 am**

Now, as to your original question; all they proved is that no two vehicles/drivers are 100% the same. As for distance traveled with windows up, A/C on or windows down, A/C off, it would depend largely on the aerodynamics of the vehicles in question, A/C compressor drag on engine vs. aerodynamic drag of windows down, wind speed and direction, ambient temperature, condition of engine, and so on.

My way of saying it is that, if even if both vehicles had the same basic configuration, identical tires, wheels, total weight (including drivers), etc., they'd only be comparing the one vehicle against the other. To adequately compare the 'A/C on' versus the 'A/C off and windows down' myth, the same vehicle should be used under the, otherwise, same conditions. Each vehicle I've driven seemed to have something unique.

8-)

Posted: **Wed May 16, 2007 8:05 am**

And I'll give them credit, there are many times they do have good, elegant ideas, and those are just as entertaining as their spectacular failures.

Oh yeah, gotta agree with you there. :)

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