New undertray design - Fuel Economy, Hypermiling, EcoModding News and Forum

AeroModder · 01-31-2010, 02:37 PM

After finally getting around to building my undertray, I got the two middle panels in. My biggest problem was space underneath the car, but I figured out a way to lift the jack higher.

Here are the two middle panels. you can see they're trimmed around the exhaust so it doesn't trap heat and/or fumes, or melt the coroplast.

Here's a picture of the front undertray I've had for a while.

There was a definite reduction in wind noise, as well as a jump in economy. My estimate is a 5 MPG gain on the highway. My daily 40-mile commute used 2/3 as much fuel than before.

Photos of the rear panel of the undertray to come, when it's finished. I'm still working on the diffuser fins.

rav · 01-31-2010, 03:15 PM

Looks awesome, great job!!

AeroModder · 01-31-2010, 07:03 PM

Thanks!

Here's the final touches on the rear diffuser and undertray panels:

I left an inch of coroplast off of the end of the bumper so the airflow separates cleanly. I put another panel on the side to seal off the open area under the trunk, and made sure to fold some of the material up so it doesn't have a parachute affect. The other side is open, though, since I need to leave the muffler in open air.

moonmonkey · 01-31-2010, 07:33 PM

the rear verticle fins look like the ones one the fusion 999 flats racer, what specicly dop they do

AeroModder · 01-31-2010, 07:58 PM

They make sure the air moving through the diffuser stay straight and non-turbulent as the air pressure drops back to the ambient pressure.

Here's a thread from here on diffusers: http://ecomodder.com/forum/showthrea...read-8313.html

Cd · 01-31-2010, 08:51 PM

AeroModder · 01-31-2010, 11:11 PM

Now that I'm looking at it more.. I found out that the maximum angle of the diffuser is 25 degrees, which is far sharper than most. However, at slower speeds, I don't think this will make much of a difference. If I needed to, I could just add a few strips of coroplast between the diffuser and bumper as a spacer.

I could also put a smaller piece on the other side, but I'm concerned about the lack of mounting points on the open side. What do you guys think?

aerohead · 02-01-2010, 02:45 PM

Quote:

Originally Posted by AeroModder

Now that I'm looking at it more.. I found out that the maximum angle of the diffuser is 25 degrees, which is far sharper than most. However, at slower speeds, I don't think this will make much of a difference. If I needed to, I could just add a few strips of coroplast between the diffuser and bumper as a spacer.

I could also put a smaller piece on the other side, but I'm concerned about the lack of mounting points on the open side. What do you guys think?

I believe that would be 2.5-degrees,not 25.The panel can go as steep as 4-degrees,depending on where it begins under the car.It's in Hucho's book.

AeroModder · 02-01-2010, 03:36 PM

The edge of the diffuser is 25 degrees from the horizontal.

I actually don't have Hucho's book, but I've heard it referenced quite a bit. Now, is there a certain angle-per-length requirement before the airflow detaches, such as no more than a 4 degree increase per foot of panel lenght?

Now I'm curious. *scurries off to do more research*

tasdrouille · 02-01-2010, 03:53 PM

Here's the figure from Hucho's book. Best angle is dependent on the aspect ratio of the diffuser (diffuser lenght/underbody lenght)