Serious Aero Mods -- Japan?

Here's something from the GasSavers.org site for those interested in serious aero modding. It seems to be a Japanese effort.

Very slick, includes rear skirts, upper grill block/removal, extended hood, and lots of other interesting details that bear close scrutiny.

http://news.windingroad.com/wp-gallery2.php?g2_itemId=36021

I like it!

But, given the overall tightness of the work, I don't understand why the wheel skirts aren't flush with the body at their upper edges where the existing body panel line is well outside the wheels.

 

The idea of trying to improve on the Prius' already outstanding Cd of 0.26, if I remember correctly, seems like an exercise in futility. Granted there is always room for improvemet, but how much and at what cost?

From readings here and there, I believe that something like folding the rearview mirrors might net Cd improvement in the fourth decimal place, removing the mirrors entirely might show gains in the third decimal place.

That said, it sure is interesting to see what efforts are being made in this regard. I also recognize that one strong element in this Captain Whiz-Bang pursuit may just be ego; Looky what I got!

Other not Prius specific fuel economy/high MPG websites have aerodynamics forums. I find it fascinating to read what owners of other cars are thinking/doing to try to get their Cd lower. Many times they are trying to create something that the Prius already has!

As an example, "wheel dams." These are little deflectors that send the air stream around as opposed to directly into the malestrom of air surrounding the spinning tires. Initially I found it hard to believe that this was an area that might produce significant results. Then I went and checked my 2008 Prius. Yes, the dams were already there. Somewhat substantial one at the front, vestigal little things at the back. Clever these Japanese.

"Out of sight, out of mind." While the full-on aero body treatment is visually engaging, from my readings I suspect that the area most likely to net the greatest improvements is under-body sheathing to keep the air moving past the aerodynamically dirty mechanical bits.

Not at all sexy, it would even be hard to picture them effectively to promote sales. I suppose you'd have to be able to show before and after Cd numbers to have any chance of marketing them. That means a wind tunnel, and that would be an expensive proposition for sure. Ergo, you don't see anyone proposing a group buy on underbody sheathing because it isn't out there to be bought.

(Yes, I know there are less technological ways to approximate Cd numbers. But we all know that such an approach would just lead to another stiffening plate like imbroglio/food fight.)

 

OK, time for some come-backs:

It looks to me that the muffler is in its normal and customary place. Here it is visible because the rear bumper is cut away, presumably to allow freer exit to air running under the car. It looks to be the OEM muffler, but then it could be the infamous TRD "fart can."

Surely, a continuous straight across lower edge would prevent the maximum amount of air from going under the car. I think the raised section has to do with road debris. Given the chance, you drive around road debris. But if that option is not available you try not to run over it with your wheels. Only option left is to drive over it. The raised section would tend to minimize damage. I suspect the mini-dams at the outer edges are meant to serve as wheel air dams.

Fortunately, it hasn't yet been necessary for me to go underneath yet. All I know about the "dirty side" of my Prius I learned from this string:

Prius aero mods (undertrays, grille block, mirror delete...) - Ecomodder.com Fuel Economy Forum

It sure looks like there are still plenty of opportunities to smooth things out under there.

 

More come-backs:

Bob, Oops, newbie error. I haven't seen the underside of my '08, so I'm in the dark figuratively speaking.

Here's a picture of the underside of an '04:

http://privatenrg.com/index.45.jpg

The green is owner added fairing. Could I assume the '04 and '08 underbodies are similar?

Pat, I'm with you on this. I not only like the cleaner fit, I like the lower scalloped edge. If I were to do/get skirts/spats, I'd want the lower edge to clear the lug nuts when the car was on a jack for flat tire removal and the suspension was unloaded. Also, the straight lower edge just looks "heavy" to me.

Tony, I'm the confused one here. I looked closely at the pix and now see what you mean. Now I see what looks like the one-great-tooth, lame-brained grin of Barney, the purple what-cha-ma-call-it! Now that I don't like.

 

I've taken a look under my 2008 and while there is a long clean underbody at the passenger area, I suspect that the front and back could use some cleaning up.

Here is some info on the latest in OEM super-clean underbody treatments:

The Audi A4: (Double-click for enlargement.)



And the Honda iCDTi:

OEM Bellypan - Honda iCDTi - Ecomodder.com Fuel Economy Forum

Here is an extensive DIY treatment, the pix tell the story. ( It's a Honda, don't know the body style.)

http://www.metricmind.com/ac_honda/pan.htm

And another on a Volvo 960:

Pictures of custom undercarriage mods. - GasSavers.org - Helping You Save at the Pump

 

Here is some both very interesting and very convincing information on the
likelihood of getting largish Cd reductions by concentrating efforts on the
forward and underside of a vehicle:

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(I do not know why these cites are being renamed "Browser Warning,"
which happens when I hit <Review Post>. I've tried them out and they still
work at the time of this posting.)

As a teaser, this info:

"(The car is unnamed but it is likely a soon-to-be-released Volvo, ie a
current, aerodynamically designed car.) [current is 2005]
"As a percentage of the total drag coefficient of 0.29, the various elements
that make up this drag are:

"Parts---------------------------------------Percentage of Total Drag
Cooling package...............................................33.4%
(including radiator, intercooler, oil cooler, etc)
Exterior...........................................................31.7%
Front wheels....................................................13.1%
Rear wheels......................................................6.9%
Floor............................................................... 6.9%
Rear Axle..........................................................3.1%
Engine..............................................................3.1%
Front Suspension................................................1.4%
Exhaust............................................................ 0.7%"
From AutoSpeed, March 9, 2005

All in all, these articles suggest that for maximum Cd improvement per
dollar spent, looking to get cooling air quickly and smoothly out of
the engine compartment and going to a different front dam/spoiler and
underbody sheathing would be the way to go.

The second article deals specifically with adding some underbody sheathing
to the front end of a Gen I Prius.

Sadly to say, there is nothing here speaking directly to the efficacy of
"skirts" or "spats" over rear wheel openings. At this point I am thinking that
they probably rate very low on the list of what might provide significant
improvements. I say sadly because they are then reduced to being only
a styling element, that is to say, eye candy. (But I still want them.)