10-01-2016, 01:24 PM
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#21 (permalink)
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aspirated rear bumper
Subaru wind tunnel testing results from 1986 would give the aspirated rear bumper a 'fail.'
*There is no 'pressure' in front of the bumper.
*Subaru found the lowest drag when the bottom of the bumper was even and flush with the spare tire well in the floor of the trunk.
*A diffuser panel,even with zero slope would help guide the air from the rear axle area to,and off the bottom of the bumper.
*Cutting holes in,or raising the bumper only aggravates turbulence and drag.Measured to 3-decimal points.
*I put this data in the seminars so you wouldn't waste your time.
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10-01-2016, 04:12 PM
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#22 (permalink)
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Ok well my new tanks numbers are in. I did 378.6 miles on this tank and used 11.86 gallons. It isn't no 100mpg, but on my way to at least 40mpg. So only having the holes in for half a tank obviously did something. I'll keep the data coming in as I go.
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10-01-2016, 04:39 PM
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#23 (permalink)
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holes/mpg
I'll find the SAE paper from Subaru and look at the delta-Cd for the bumper data and see if it's significant enough to even show at the gas pump.
I'm happy that your economy is up.I'm just not certain that we can make an association with it to the bumper.The science suggests that it would be an impossibility. 
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10-01-2016, 04:58 PM
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#24 (permalink)
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Quote:
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So only having the holes in for half a tank obviously did something.
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One data point (half a data point?) does not rise above the noise of environmental variables. See: Coupe 69 mpg.
From what I think I've been taught, the holes will increase drag. |
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10-01-2016, 05:49 PM
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#25 (permalink)
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Quote:
Originally Posted by aerohead
I'll find the SAE paper from Subaru and look at the delta-Cd for the bumper data and see if it's significant enough to even show at the gas pump.
I'm happy that your economy is up.I'm just not certain that we can make an association with it to the bumper.The science suggests that it would be an impossibility. |
Not taking away from what has been done before but looking at the design of how the rear of this car is made lots of air is forced into the rear bumper I'll snap a few photos when I get home to show it.
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10-01-2016, 05:51 PM
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#26 (permalink)
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Generally what happens when you have a scoop with no rear outlet, is that it becomes a high pressure zone and air flows around it. You expend the energy necessary to maintain that high pressure zone, but it may or may not be more than the energy needed to create the turbulence you'd get behind the bumper by allowing the air through.
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10-01-2016, 08:00 PM
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#27 (permalink)
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Ok here is what it looks like when looking through the holes. Both sides are the same and go through one of the holes and almost halfway into the second. So before all this air was just ending up hitting the wall and then down. Seems like it would be more free flowing now.
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10-01-2016, 08:14 PM
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#28 (permalink)
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Consider the front of the car - we close up grilles because it's often better for air to not flow at all through an aerodynamically dirty area. If the air has no way to get through, it simply won't go there. Again, I could maybe see some benefit to filling some of the vacuum left in the wake of the car, but this would be a very aerodynamically dirty way of doing it.
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10-01-2016, 09:35 PM
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#29 (permalink)
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It hasn't hurt yet so I'll stick with it lol 
Weather is starting to get very crappy here quick. The rainy season is upon us. I will keep posting numbers as I go only thing is I'm doing other things also so I hope it doesn't mess the numbers up to bad. Mainly just bumping tire pressure, and blocked the upper front grill. Gotta look into more things before I jump in deeper. My number I'm shooting for is 40. So I'll have to hit over 400 miles in a tank to get there 
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10-02-2016, 04:05 AM
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#30 (permalink)
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Congrats to you. Be happy with your results, reagrdless what did it.
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