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Old 01-08-2008, 07:57 PM   This thread is in the EcoModder Project Library | #1 (permalink)
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Autospeed article: adding a chin undertray to a 1st gen Prius

(Note: see also Adding front & rear undertray to 2nd gen. Prius )

From the Australian web magazine Autospeed -

Some of you may have seen these already...
Modifying Under-Car Airflow, Part 1

Modifying Under-Car Airflow, Part 2
Originally these articles used to be pay-access only, but they've opened them up for public access now.

The project documents the creation of a prototype front partial undertray for a 1st gen Prius, testing, and then fabrication of a permanent version.

Before:



Mockup:



Final version:



The writer reports a 10+% improvement in fuel economy at freeway speeds (100km/h) with the mod in place. I frankly find that a bit difficult to believe, though I don't doubt there was some improvement.

If you read the article you can find a few holes in his testing approach - even though he's fairly aware of things like experimenter bias, and aiming to perform tests on the same day (for consistent weather conditions).

The articles also give a good background on the subject of under car aerodynamics. Definitely worth a read if you haven't seen them yet:
Modifying Under-Car Airflow, Part 1

Modifying Under-Car Airflow, Part 2

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Old 01-14-2008, 08:26 PM   #2 (permalink)
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These are great articles

Sure their testing left something to be desired.
And I would question their results.
C'mon ten percent improvement?

However, I can see how I could apply what I learned in this
article to the '94 Honda Accord I currently drive.

Thank you, MetroMPG for finding this article.
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Old 01-14-2008, 08:29 PM   #3 (permalink)
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Good stuff, Metro...thanks for sharing!
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Old 01-15-2008, 03:36 PM   #4 (permalink)
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Ditto. Thanks for dredging that up, Metro.

I noticed they use "high quality" duct tape for their mods. Something we home DIY'ers can shoot for. I tend to use black duct tape, so it matches the trim on my car. A real consideration, since my temporary grill block stayed on the car for six months.

IMHO, they are not hard-core hypermilers, though. I see they chose stability over low drag. Wimps.

Thanks again,
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Old 01-15-2008, 03:57 PM   #5 (permalink)
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Quote:
Originally Posted by s2man View Post
I see they chose stability over low drag. Wimps.
I know!

When I read the bit about the front tire deflectors they also tested along with the undertray, I couldn't believe it they concluded: they also reduced drag, but made the front feel end lighter, so we ditched them.
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Old 01-15-2008, 07:12 PM   #6 (permalink)
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Yikes!! My Aveo has absolutely NO chin undertray!! I can see clear up to the hood from under there. With grill blocks, maybe I can top their 10% WOO HOO!! Weekend project!!
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Old 01-15-2008, 07:29 PM   #7 (permalink)
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It may not need one as much as this Prius did.

It's not so much an issue of being able to look up & see the hood, as it is directing airflow more cleanly past the bits of the car that stick down below the bottom edge of the front bumper.
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Old 01-15-2008, 07:37 PM   #8 (permalink)
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I'll have a look when my Mother in law is done borrowing it. As I recall though, it isn't especially aerodynamically clean under there.
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Old 01-15-2008, 07:45 PM   #9 (permalink)
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BTW. I noticed the undertray on my wife's Taurus while I was working on it, and got undertray envy. So I grabbed one off a Taurus last time I was at the junkyard. It's not solid; it has a couple of slots in the middle to allow air for cooling, I guess. It feels like really thick polyethylene. Should be easy to cut down and fit on my Cavalier.
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Old 01-15-2008, 08:57 PM   #10 (permalink)
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Quote:
Originally Posted by s2man View Post
I noticed they use "high quality" duct tape for their mods.
Duct tape is AMAZING

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