Project: Geo Metro boat tail prototype - 15% MPG improvement @ 90 kph / 56 mph

[MetroMPG]

guitarguy: no, the fairing behind the wheel wasn't tested. (Meaning there's room for further gains )

Topher: You wouldn't be able to just add a Kammback + boat tail combo on a Metro and predict a ~20% improvement (Kammback was ~4.9 %)

All the other aero stuff I've done upstream affects the performance of the tail - meaning it wouldn't work as well without these:

• partial grille block,
• headlight gaps sealed
• hood/bumper gap closed
• pass mirror delete,
• partial cowl block,
• wipers were off
• smooth wheel covers
• rear fender skirts
• and the big one: full smooth undertray
• EDIT: forgot radio antenna delete

[MadisonMPG]

Holy crap. You are talking INSANE numbers for a non leanburn engine. 75 mpg is now possible... take THAT GM.

[MetroMPG]

GM and all the other automakers know that 75+ mpg is possible from a light, low drag vehicle with a conventional engine.

(EDIT: a vehicle they are convinced will not sell in large numbers - and they're probably right.)

Dr. Paul MacCready predicted that a car,like the Impact (GM EV1, Cd 0.195) ,if produced as a gasoline-powered car,would achieve upwards of 100-mpg. -- aerohead

It's easy to find examples of streamlined concept /prototype cars with conventional drivetrains that get exceptional mileage.

[Christ]

concept/prototype... what about real world? Not so easy, eh?

Darin - yeah, the excitement led me astray..> I forgot your car was also altered in other ways. Still, a very nice gain.

Plan on testing those wheel tails any time soon?

[thatguitarguy]

As difficult as it would be to install/remove the undertray, I don't suppose you did A-B-A testing with that, but do you have any figures or a good guess as to how much the difference the undertray by itself would make?

[MetroMPG]

I did A-B testing only on the undertray (because it was difficult to re-install, as you said).

It showed about a 2% improvement.

The numbers I have from the undertray + the boat tail suggest the combination of the two is greater than the sum of their individual effects taken separately.

Meaning: if I were to leave the boat tail on, and test just the undertray, we'd see greater than a 2% improvement from it (because the best maximum performance of the boat tail depends on the smooth flow provided by the undertray).

[MetroMPG]

Originally Posted by Christ

concept/prototype... what about real world? Not so easy, eh?

Easy to build. Harder to sell, I suspect.

Plan on testing those wheel tails any time soon?

Nope! Gotta save something for next summer.

[Christ]

Summer isn't too far off, my friend. Just think, Winter's coming soon, and then comes the Vernus (Spring), and then comes Summer. I'm sure you'll be working on something during the spring time, no?

[Nerys]

WOW. ok I think I am going to have to build one of these I am truly shocked it was THAT BIG and that big EVEN WITH the already in place Kamback improvements.

If your up for it (I KNOW its a ton of work) unless you already have the data?? ie what kind of improvement would JUST the tail make over a stock car? no belly no wheel skirts etc.. anyway to calculate that?

truly wow. Time to go find some coroplast!

I also wonder if I can test angles WITHOUT driving. IE big massive fan into a difuser array to straighten the airflow (think wright brothers wind tunnel)

I could aim the fan in the direction I want to test put a panel with tufts in place and adjust to see the changes in real time in the drive way.

do you think this would work?

[brucey]

I really want to re do my tail now after seeing a 15% increase in yours. Damn!

Mine showed up absolutely nothing. But it also was a lot steeper. I fail.