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Old 12-27-2007, 02:46 PM   #11 (permalink)
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Ah, I have seen that paper before, but it's worth another read.

Really, .31? Every source says something different...But yeah, you would get a lot of good out of aeromods.

You weren't "Wrong" on the fuel economy, but there are different tests used by the EPA these days compared to the old tests.

I think if you could get 250+ pounds removed it would be worth it. I would strip the interior and things as well.

I'm not sure on .25 out of just that. Compare to the insight, which is rather definitively known to be a stock .25...Some wheel covers and a boattail would definately help. Mehbe treb will chime in, but he has a breakdown of where aero drag occurs and I think about a 1/3rd is after the car in the wake.

I doubt how much electronics will help on a highway trip. It's already doing fairly well with the lean burn and you won't be stopped too much. However, combined with good aeromods and LRRs, I think driving technique could bridge that gap.

I think I'm something like 80% over epa in my car, but then I started with an auto...darin has done 130+ mpg circuits with his metro. *shrug*

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Old 12-27-2007, 02:47 PM   #12 (permalink)
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Quote:
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What would the modifications I'm considering get you? Under 0.2? There are probably diminishing returns to aeromods at some point.
Fundamentally - there's no diminishing returns for cD - it's actually the opposite .1cD versus .2 cD halves for the force... .2 vs. .3 is a third

But, the mechanics half has to be able to keep up. Less force to overcome isn't any good if you're power plant is too big to begin with.

It's just exponentially more difficult to lower cD the further down you go. Not diminishing returns - just exponential investment
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Old 12-27-2007, 02:51 PM   #13 (permalink)
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^^ For everyone... Keep in mind that cD isn't anything like HP.... Unlike something like a WAI etc. it's a bit more difficult to predict a number (even a range) of cD reduction. And of course, no one thing will be the savior of poor aero design - it's a package deal.
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Old 12-27-2007, 03:02 PM   #14 (permalink)
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Common misconceptions about the EPA test

Guys, the EPA mileage test has not fundamentally changed since it was first instituted in 1975.

What has happened is that in 1985 and 2008 the EPA has appled "reduction factors" to make the mileage more realistic.

Look at that paper that I linked to, they discuss the 1985 reductions.

The CAFE standards written into law use the original 1975 standard, BTW. So my Saab 9-3 2.0T, which got 28 mpg under the 2007 standard and gets 26 mpg under the 2008 standard, has a CAFE number of 34 mpg.

Neither here nor there, but I did want to clear up that misconception.
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Old 12-27-2007, 03:09 PM   #15 (permalink)
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Quote:
Less force to overcome isn't any good if you're power plant is too big to begin with.
Interesting point. Maybe 97 hp is too powerful for what I want to do.

Anybody ever turn a 4 cylinder into a 3 cylinder? Plug off the ports, take out the piston and con rod? Probably throw some wicked codes!

Another alternative might be the industrial diesel engine route. Briggs and Stratton makes a 3 cylinder industrial turbodiesel that makes 37 hp.
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Old 12-27-2007, 03:11 PM   #16 (permalink)
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The B&S honestly sounds like a great idea. Match it to some ridiculously tall geared 5th that has it plugging away at 1k rpms at ~50 mph and you'd be set.
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Old 12-27-2007, 07:18 PM   #17 (permalink)
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Quote:
Originally Posted by Krieg View Post
Guys, the EPA mileage test has not fundamentally changed since it was first instituted in 1975.

What has happened is that in 1985 and 2008 the EPA has appled "reduction factors" to make the mileage more realistic.
Sweet - my outdated knowledge hasn't let me down
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Old 12-28-2007, 09:22 AM   #18 (permalink)
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2 relevant Ecomod rides

Well, I looked through the garage, and there are 2 Civics that could be templates for my AXP ride.

Aerocivic is a DX hatch with heavy Aeromods. He averages almost 70 mpg.

Thrifty McGasaver has a VW with some of the mod's I mentioned (carbon fiber hood, lowering springs), yet he can't even hit the EPA numbers!!!!

Damn it! This is going to be harder than I thought.
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Old 12-28-2007, 09:48 AM   #19 (permalink)
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Looks to me like his lifetime AND 90 day average are over the New EPA Combined number of 43mpg. These cars need to be driven gingerly to achieve these numbers. It doesn't happen by just slapping together top shelf parts.

Yes, it looks like you have your work cut out for yourself. But if it was easy, everyone would do it.
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Old 12-28-2007, 11:32 AM   #20 (permalink)
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Don't get me wrong...

... I knew there would be work to be done. Hacking the electrical system to make it a mild hybrid, for example.

I'm a mechanical engineer, not an electrical engineer. So the hack would tax my skills.

But it looks like waaaay more engineering is needed is needed. More than just buying some parts and installing them (for which I am fully competant).

I'm now thinking that I might have to custom fabricate some carbon fiber suspension components. Carbon fiber halfshafts, anyone? Carbon fiber control arms? Front Subframe?

How do you cut 500 lbs. from a car without gutting the interior?

Engine swaps? Especially gas to diesel swaps? That's tough stuff. A diesel doesn't help the lightening process, either. They're all cast iron. Very heavy.

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