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Old 06-07-2007, 10:49 AM   #1
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coastdown hill

This thread inspired by:

1 - psyshack's recent Coast down test , and,

2 - CoyoteX's reports of testing his aero mods by seeking terminal velocity on the same hill (Playing with Lawn Edging)
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Old 06-07-2007, 10:58 AM   #2
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It's got me thinking: there might be a better hill just a little further away that will have a higher terminal velocity. Stands to reason that the higher that terminal velocity, the more likely aero changes will reveal themselves...
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Old 06-07-2007, 11:08 AM   #3
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Can you tell if the percent increase or decrease jives with the on the road SG test?
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Old 06-07-2007, 11:14 AM   #4
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I could try. Most of the aero mods I've tested at a constant speed on the test route have yielded similar sized results on FE - in the range of 2-3%.

So they should have similar end points on the coasting test.

It won't be useful for figuring out actual FE effects, only relative differences between stuff. Which is fine with me. I figure if I can uncover a discernable change on the coastdown, I may then go out and measure it at a higher constant speed on the flat test route.

I'm thinking: monster air dam
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Old 06-07-2007, 12:45 PM   #5
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Quote:
Originally Posted by MetroMPG View Post
... I'm thinking: monster air dam
Air dam =
My air dam includes a nice forward belly pan, goes from air dam to approximately the front axle line. For the whole package, I definitely see an improvement since completing it (I had a couple threads here re. the air dam around the last weekend in May).

I have to admit I don't have an apples-to-apples comparison test. The weather is warmer and I boosted my tire pressure a couple pounds. But since then I've been consistently between 30-32 mpg while before it was basically between 27-30.

I see a big improvement in the glides. For any given glide, it goes further now. Many times I can get significantly up the next hill while still gliding where I used to need to go back in gear to get up the hill.

I hope to do rear wheel skirts next. I want to call them pants since my car is named Sven.
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Currently getting +/- 50 mpg in fall weather. EPA is 31/39 so not too shabby. WAI, fuel cutoff switch, full belly pan, smooth wheel covers.

Now driving '97 Civic HX; tires ~ 50 psi. '89 Volvo 240 = semi-retired.
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Old 06-07-2007, 01:02 PM   #6
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Pantless Sven, we want data!

I love that people are trying aero stuff, but it's better when they isolate the mods and gather results. Otherwise how can you be sure you're not fooling yourself?

How hard is it to remove the dam? If it's not difficult, a coastdown ABA wouldn't be too hard to do.

----

On another note, this afternoon I went to the other 4 "big" hills that are nearby and the most I saw was 30 mph max on any of them, so they're not quite as good as the one I went to this AM. (Can you tell I'm getting lots of work done today?)

There's one other hill literally minutes from the house that I'm sure would coax upper 30's mph on the descent, but there's a railway crossing with brutal bumps and a traffic light in the run-out zone.
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Old 06-07-2007, 01:23 PM   #7
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When you did the hatch test, was that with the hatch just open, but down, or was that with the hatch at the top of it's travel?
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Old 06-07-2007, 01:30 PM   #8
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Quote:
Originally Posted by MetroMPG View Post
I could try. Most of the aero mods I've tested at a constant speed on the test route have yielded similar sized results on FE - in the range of 2-3%.

So they should have similar end points on the coasting test.

It won't be useful for figuring out actual FE effects, only relative differences between stuff. Which is fine with me. I figure if I can uncover a discernable change on the coastdown, I may then go out and measure it at a higher constant speed on the flat test route.

I'm thinking: monster air dam
Like sooo. . . . . ginormity???

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Old 06-07-2007, 01:51 PM   #9
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Quote:
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... How hard is it to remove the dam? If it's not difficult, a coastdown ABA wouldn't be too hard to do ...
Um, keep your pants on. Unfortunately removing the air dam would be a fair sized PITA.

I may get a chance to retest it without the air dam. A friend is interested in molding the dam in fiberglass which would require temporary removal of the oem air dam plus my extension as a unit, which is pretty easy. If he can loan me a spare OEM one then I can do a comparison. Don't know if I can/will do a coastdown test but if he provdes an OEM one then at least I'll get to drive it a bit.
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Currently getting +/- 50 mpg in fall weather. EPA is 31/39 so not too shabby. WAI, fuel cutoff switch, full belly pan, smooth wheel covers.

Now driving '97 Civic HX; tires ~ 50 psi. '89 Volvo 240 = semi-retired.
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Old 06-07-2007, 04:15 PM   #10
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MetroMPG: I found where your test was done with the hatch full on open. I looked at the link and searched and I couldn't locate any test that was done with the hatch unlatched, but not raised. Was their a test with the hatch just cracked open, like with a broom handle or something?
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