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

[MetroMPG]

Originally Posted by Cd

And the area behind those mudflaps ... ? ( ducks for cover )

Have to save something for later!

[Nerys]

and 97cents in black spray paint? come on you know you want too! will make it last longer too!

have you worked out a way to make it stowable yet?

[MetroMPG]

This is just a proof of concept - not planning to save it.

So no black spray paint. But sounds like you'll be happy to hear I'm going to skin the top & sides in black plastic (garbage bags, pulled taut) for tuft testing, to cover up the lumpy bits and lots of seams in the cardboard that are going to mess with the tufts.

So it'll look nice, briefly, until I tear it apart and put it out with the recycling!

Nope, haven't yet decided on how I'll make the stowable version based on this one.

If I had room to store it, I'd just make a rigid, non-stowable version that disconnects.

[MetroMPG]

Finished "blending" the undertray into the bottom of the tail today.

Then I recorded more tuft tests. Haven't looked at the video for results yet, but based on a couple of stolen glances at the laptop underway, I'm pretty sure it's better.

Got the taut garbage bag skin on, which helps even out and hide the dips & seams. Tuft testing the top & sides is next on the to-do list.

The last test will be an A-B-A comparison at highway speed on my flat, straight test road.

Until then: more pictures!

Below: undertray from 2 angles:



The angle of this pic makes it look like the cardboard is close to the muffler, but there's a 3 cm (~1.5 in) gap at the closest point; most of the cardboard is over 2x that distance away. Also, it's not enclosed as it might appear, it's fully open to the wheel well.



Below: plastic skin & view from above:

[MetroMPG]

Oh yeah! Just watched the videos - way better flow! No surprise, right??

Also saw an interesting change in the direction of flow near the edge of the bottom, about half way down the length of the tail.

Before adding the undertray, the flow seemed to be wrapping down from the side towards underneath (going aft at about a 45 degree angle), and now it appears to be flowing from the bottom toward the side.

Suggests the undertray has increased pressure beneath the tail higher than it is on the lower left side, where the reverse was true without the tray.

I'll make a diagram or screen cap to show it best. Which is coming, eventually.

[Cd]

I noticed that several members here have installed belly pans made of Coroplast. What puzzles me, is that the only areas that you guys seems to be covering with metal ( or metal tape actually ) are the areas near the muffler.
MetroMPG, how are you handling the heat of the engine and transmission ?
It appears as though some of you guys are so bold as to have the Coroplast sitting flush against the engine.

You have done a really impressive job of smoothing out that underbelly !
Looking forward to the tufting !

[pgfpro]

Originally Posted by MetroMPG

Oh yeah! Just watched the videos - way better flow! No surprise, right??

Also saw an interesting change in the direction of flow near the edge of the bottom, about half way down the length of the tail.

Before adding the undertray, the flow seemed to be wrapping down from the side towards underneath (going aft at about a 45 degree angle), and now it appears to be flowing from the bottom toward the side.

Suggests the undertray has increased pressure beneath the tail higher than it is on the lower left side, where the reverse was true without the tray.

I'll make a diagram or screen cap to show it best. Which is coming, eventually.

Man you do awesome work!!! I have learned a ton from all your posts.

Thanks so much

[NeilBlanchard]

Hi Darin,

Looks great! I have a question, similar to Cd's, about heat from the exhaust; especially from the catalytic converter? Some air used to come through the engine and then pass along the exhaust tunnel, right? Now, that path looks to be nearly sealed up, so I'm curious about heat that is not getting dissipated from the exhaust system.

[3-Wheeler]

Originally Posted by Cd

It appears as though some of you guys are so bold as to have the Coroplast sitting flush against the engine.

Cd,

My fiberglass belly pan fits within about 1/4 inch of the engine sump pan. And don't forget that there is foam inside the two layers of glass.

I hope this means that the oil pan does not get that hot, since the foam starts to distort at temps over 250°F or so.

Jim.

[MetroMPG]

Bottom tufts before & after adding the belly pan.

(Keep in mind this is entirely subjective interpretation on my part...)

Before:



After