Mythbusters "tests" efficiency of dimples vs. smooth, and clean vs. muddy car

[MadisonMPG]

I think we should write in.

[darcane]

Originally Posted by pgfpro

They did a very poor test on this one and should of known better.

The amount of fuel that would be measured roughly would have been .06 lbs total and a difference of .0066lbs or 3 grams of fuel.

They needed to travel a longer distance.

A longer distance certainly would have helped....

But check your math.

IIRC, they made five trips of one mile, but they measured after each and averaged them.

At 26mpg I get:
1 mile at 26mpg = .0385 gallons.
.0385 gallons x 6.25lbs/gal = 0.241 lbs of gasoline.
.241lbs = 3.86oz or 109g

At 29mpg I get:
1 mile at 29mpg = .0345 gallons.
.0345 gallons x 6.25lbs/gal = 0.216 lbs of gasoline.
.216lbs = 3.46oz or 98g

That's certainly a measureable difference.

[Old Tele man]

...did anybody "catch" the weight values mentioned after each test?

...California has "boutique" gasoline(s) so maybe their weight-per-gallon values were different than typical 6.1 to 6.2 lbs/gal? 6.25 lbs/gal sounds kinda "dense" to me.

[pgfpro]

Originally Posted by darcane

A longer distance certainly would have helped....

But check your math.

IIRC, they made five trips of one mile, but they measured after each and averaged them.

At 26mpg I get:
1 mile at 26mpg = .0385 gallons.
.0385 gallons x 6.25lbs/gal = 0.241 lbs of gasoline.
.241lbs = 3.86oz or 109g

At 29mpg I get:
1 mile at 29mpg = .0345 gallons.
.0345 gallons x 6.25lbs/gal = 0.216 lbs of gasoline.
.216lbs = 3.46oz or 98g

That's certainly a measureable difference.

Your right I forgot I still had my engine settings set on a four cylinder in my spreadsheet and forgot that my numbers are fuel flow per injector.

So my figures came out to be 106grams and 96 grams with a difference of 12grams based on a specific gravity of 0.728, in which is measurable but still way to small of an amount to conclude a accurate test.

I still need to see the show. Did they do a ABA test? Because I know for fact that the fuel injection system will hold more or less fuel then 12 grams based on fuel temps alone.

[Old Tele man]

...no ABA tests.

...looked more like five each "flying-mile" runs through a 1-mile distance at 65 mph, with speed run-ups prior to the measured mile.

...in fact, it wasn't clear whether they reversed the run directions to cancel wind / terrain incline, etc. or not, because it seemed to appear they were making "backyard" loops over paved closed roadway (flying through road crossings is why).

[pgfpro]

Originally Posted by Old Tele man

...no ABA tests.

...looked more like five each "flying-mile" runs through a 1-mile distance at 65 mph, with speed run-ups prior to the measured mile.

...in fact, it wasn't clear whether they reversed the run directions to cancel wind / terrain incline, etc. or not, because it seemed to appear they were making "backyard" loops over paved closed roadway (flying through road crossings is why).

WOW!!!!

That surprises me. They're usually much better then that!!!

It looks like its on tonight on Discovery at 9:00pm so I going to have to watch it.

[RobertSmalls]

Originally Posted by MadisonMPG

I think we should write in.

Yes, they have a forum for that sort of discussion.

[majestic]

they really screwed the test by picking a tauras with a rear spoiler.

the clay models spoiler is shaped (regardless of surface) a million times better than stock.

[Christ]

Originally Posted by bomber991

They clayed the whole car smooth, which added some weight, but then they did 5 runs and averaged them. Then they made the dimples and even put the little caps they carved out into the car so that the weight was the same as before, and then did 5 more runs and averaged them. The way they measured the fuel is probably more accurate than using a scangauge.

"26 and change" mpg for the smooth car
29.65mpg for the dimpled car

Now where's the 11% improvement? 29.65/26=1.14 That would mean it was 26.7mpg when smooth wouldn't it?

The problem is that it wasn't really accurate at all. At 65 MPH, Adam had like .1 seconds to react and flip that switch, both times. Human error is accountable here, as well. Also, there are far too many potential variations to count a 1 mile stretch as valid.

There is no way their "test" was more accurate than using a tuned scan gauge. Unfortunately, it's what I've come to expect from them.

[achang1]

if anyone wants to watch it its at
zSHARE - mythbusters.s07e14.hdtv.xvid-lmao.flv



edit: anyone wanna fabricate some dimpled body parts and test it out?