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

[Nerys]

I am curious about the guino. The reason I have NOT gotten one is that everything I have read says they are basically useless. ie you "fine tune" them so they "jive" with your tank to tank readings but the moment you upset the "tune" ie drive any differently than with the tanks you used to tune it all the tuning is for naught.

Granted I have not looked into them recently. Have they made that much improvement?

Makes me wish I had a 96 but the "simplicity" of the pre 95 vehicles eliminates that desire quickly :-) my 94 is a ton load easier to take apart and repair than the 95+ metro's

I may have to give it another look. I am itching for a new project to work on.

[MetroMPG]

The MPGuino is arguably more accurate than a ScanGauge due to the way it measures fuel use. Yes, it needs to be set up and calibrated to the individual vehicle, but so does a ScanGauge. Check the Guino subforum for more information.

Data points. I have driven this route in excess of 450,000 miles over the last 15 years. I would say thats a pretty decent set of data points to work with :-)

As to why your mountains of data aren't showing you the information you're looking for, why not start a new thread and post the data? The topic of why you can't find more than a 2% fuel economy change by slowing 10 mph on the highway is threadworthy on its own.

[MetroMPG]

Originally Posted by Christ

Darin -

Any further iterations of the boat tail on your mind for future (read: Spring) testing?

Nothing specific other than I'm leaning toward a fabric covered frame for the "final" version. Maybe something like tough tonnea cover material.

And toying with the idea of finding myself another rear bumper skin that I can modify to incorporate the fairing behind the rear wheels, plus attachment points for the lower part of the boat tail frame.

(I'm reluctant to "wreck" the original bumper by hacking it up & glomming things onto it. Not sure why... I doubt I'll ever enter this car in any concours d'elegance... or even sell it for that matter. Irrational concerns. Car culture influences.)

[Nerys]

get another bumper? they are usually cheap since its just a cover and you can then just "swap it back" if you really have the need or desire too.

[Christ]

Originally Posted by MetroMPG

Nothing specific other than I'm leaning toward a fabric covered frame for the "final" version. Maybe something like tough tonnea cover material.

And toying with the idea of finding myself another rear bumper skin that I can modify to incorporate the fairing behind the rear wheels, plus attachment points for the lower part of the boat tail frame.

(I'm reluctant to "wreck" the original bumper by hacking it up & glomming things onto it. Not sure why... I doubt I'll ever enter this car in any concours d'elegance... or even sell it for that matter. Irrational concerns. Car culture influences.)

I'll keep an eye out on my local CL's and such and if I find a rear plastic for you, I'll pick it up and hang onto it. Eventually, someone over this way will be going to see you, such as the next GGP or whatever, and can take it up to you, I'm sure.

[aerohead]

Originally Posted by Nerys

I do not doubt the data. but part of good science is being able to reproduce data which is what I tried to do.

steady state or not 15% improvement "should have" shown up as more than a 1 or 2% difference in 400miles of driving where each leg is 54miles 1:20 minutes (basically that times 6)

if even 50% of my trip is relatively steady state (its much more than that but I don't have hard numbers) that means I should see at least a 7-8% difference.

then again It could also be my car. I might have something failing thats dragging me down (lately I have been maxing at 40-42mpg but its also been REALLY cold and really windy the last few weeks which might explain that.) so I have not tried to do it again till I have more consistent figures. because I damned well would slow down 10mph if it meant I could gain even 5% FE improvement :-)

One of my SAE papers took EPA Mobile Sources to task,claiming that a 20-mile warm-up before mpg testing was not adequate,and that in their own testing,reproducibility could not be achieved without 45-miles of driving.
It could be that the 54-mile test legs are not adequate.
Another paper claims that in an 11-mile cold-start commute,that the mpg in the last 6-miles is 50% better than the in the first 5.
Beyond a single variable during testing,making sense of the results can sometimes require the use of a super-computer and very sophisticated programs.

[3-Wheeler]

Nerys,

Since your Metro mass (weight) is close to the Insight, and your engine size if fairly close, and air drag due to Cd only slightly higher, then your straight line driving mileage should be better at a slower speed. If not, then like you mentioned earlier, there may be something to look at when the weather is warmer.

Just trying to help...

EDIT:
Almost forgot...

My daughter and I ScanGauged her Toyota Echo two years ago on a warm summer day (sounds good right now) and it easily got 55 mpg at 45 mph. She is a pretty good Hypermiler. Her mileage on the Interstate is 46 mpg.

I started Hypermiling the Cavalier back in the Spring of 2007 and got a 20% increase, and the same with an old crusty Honda 500. Both showed quite the improvement just by primarily, slowing down to 45 or so.

Jim.

[3-Wheeler]

Hi Metro,

Say, are you thinking of doing something like this with the extreme end of your boat tail?

Maybe an extended lip, but not as long as this one??

Just curious. If it allows the air to separate better, it may be useful on another boat tail project coming up...



Jim.

[MetroMPG]

Jim, you're posting some really good Insight gen. 1 coast down info in this thread. I'm going to split it off into a separate topic so your work isn't buried in the chatter about the Metro boat tail.

I'll post back here with a link to the thread once I move things over...

EDIT: here's the link ...

http://ecomodder.com/forum/showthrea...1-a-11826.html

.

[MetroMPG]

Originally Posted by 3-Wheeler

Say, are you thinking of doing something like this with the extreme end of your boat tail?




Jim.

I'm actually considering doing something like that more to the rear bumper, but more to give myself a clean mounting point for the boat tail than anything else.

The Kamm back I made for the car already gives it some of that appearance, and will be useful for attaching the upper portion of the boat tail.

As for the effectiveness of having an open "pocket" at the rear of the vehicle, vs. a clean chop and a solid surface, Phil has posted some information that the solid surface may be better for drag reduction.

Cd (the person) will hopefully remind us about the university that designed a shallow indentation in the "transom" of an aeromodded Ford Taurus (if memory serves) that they claimed helped Cd more than a flat surface. EDIT: Washington University, and it was one of their "Viking" experimental cars.

But the thinking seems to be that a wide open space at the back of the car isn't optimal (such as with my Kamm back, and the fairings on the Prius shown), even though it may improve drag over the unmodified shape.