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-   -   MINI Cooper S rear diffuser w/ underpanel (https://ecomodder.com/forum/showthread.php/mini-cooper-s-rear-diffuser-w-underpanel-15189.html)

curv872 11-17-2010 12:36 PM

MINI Cooper S rear diffuser w/ underpanel
 
From the rear valance, my design extends back 26" to the rear subframe and is nearly 4ft wide. From the subframe, the underpanel begins a gentle rise at the same angle another 12" back. So we are talking about nearly 12 square ft of area acting on the air.

http://img72.imageshack.us/img72/4629/venturism8.jpg

A and B of diagram above, the best angle for drag reduction (CD) is from 2 and 4 degrees.

A (like mine), the best angle for reducing lift (CLR) is 6 degrees.
B, the best angle for reducing lift (CLR) is 11 degrees (at the expense of increased drag)

Made out of black coroplast, total weight with strakes, just over 4lbs.

http://lh6.ggpht.com/_tPeOcA9yGbA/TM...Y/IMG_4341.JPG
http://lh6.ggpht.com/_tPeOcA9yGbA/TM...M/IMG_4342.JPG

Visual indication of how far back the 6deg rake goes back to combine with the flat underpanel:

http://lh3.ggpht.com/_tPeOcA9yGbA/TM...mNBY/angle.jpg

Now for the shocking results!

I drive the same commute to work everyday and usually average about 26-27mpg. After logging 106 miles with the diffuser, I filled it back up with 3.538 gallons....that's now an avg of 29.9mpg!!!:eek:

Joe

dennyt 11-17-2010 01:22 PM

Awesome! Beautiful diffuser. How did you close out the coroplast edges, and how did you mount the strakes?

curv872 11-17-2010 01:27 PM

Thanks!
Just used painters caulk to close the trailing edge...I may revisit to clean the edge a bit more. For the strakes I had a brainstorm...they are coroplast pieces folded in half so bottom edge is perfectly flat...which also made them much more rigid. They reside in aluminum C channel adhered with Gorilla Glue.

Quote:

Originally Posted by dennyt (Post 204605)
Awesome! Beautiful diffuser. How did you close out the coroplast edges, and how did you mount the strakes?


curv872 11-17-2010 01:57 PM

Here is a view of the top side:
http://lh5.ggpht.com/_tPeOcA9yGbA/TN...I/IMG_4390.JPG

wdb 11-17-2010 03:57 PM

I'm jealous! I'm certain my Fit would benefit from a rear diffuser, and it would be relatively easy to do. Please let us know if your improved results hold up over time.

curv872 12-22-2010 01:18 PM

Another 302.1 miles, this time 26.9mpg (some of which was stuck in traffic, so i'm happy).

COcyclist 12-22-2010 03:47 PM

Quote:

Originally Posted by curv872 (Post 204612)

Nice work! It looks great and I think you will continue to see good results. I did a similar thing from just behind the catalytic converter and I am amazed what it did for my mpg. I may have to add some strakes like yours. I used some thin aluminum roof flashing to fill in between the fender liner and the diffuser. I'm in snowy Colorado and I didn't want that filling up with slush and snow.

UFO 12-22-2010 04:38 PM

The area where you put your diffuser was just open chassis before? Presumably it meets your belly pan on the leading edge...?

It looks like a really nice job, I hope I can make one just as nice for my Beetle.

Mario_Marques 12-26-2010 08:19 PM

Really nice work! Very clean, it looks life factory car!

curv872 01-16-2011 11:51 AM

After more logging, on average, my freeway mpg has increased 1mpg to 27mpg. I'm very pleased with the results!


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