New undertray design

[AeroModder]

Thanks for the diagram! I'll do some measurements and find out where I'd be on the chart. Also, my diffuser is rounded, and Hucho is showing a linear diffuser, so that adds to the complications here. Looks like my diffuser is far from optimal. Back to the drawing board!

[MetroMPG]

AeroModder: you should add your vehicle to the garage so we know what you're working on without having to ask all the time. (The info will then appear under your avatar.)

[AeroModder]

After driving through another tank, the difference with the completed undertray and diffuser, and driving 10 MPH slower on the highway, only showed a 1 MPG difference, which is within a margin of error.

Needless to say, this is very dissapointing.

At first, I thought this may be due to some kind of mechanical issue. When attempting to inspect my catylitic converter (since it is 18 years old), I noticed water pouring from the air hoses. I'm wondering if it is partially corroded on the inside, and may need replacing.

However, after a more critical inspection of the undertray, I've found a place that is most likely catching air and creating drag. The bolts had loosened up somewhat, so I retightened them and did my best to seal off that area.

We'll see what happens with the next tank, whether the issue is mechanical or aerodynamic. Any advice would he helpful.

[stonebreaker]

Question: Did you add your mods all at once or one and test, one and test?

[moonmonkey]

how about some pictures of your pan, cant diagnose what we cant see.

[JasonG]

Somebody else had a similar issue with a partial bellypan. They made a big parachute from the rear bumper to the rear axle.
Send pictures please.

[AeroModder]

Here's the thread: New undertray design

Also, another photo: http://i3.photobucket.com/albums/y93.../Undertray.jpg

I didn't take a picture of the new modification, though. I know the pictures are low-quality. I don't have a camera yet, and it's from a cell phone.

Stone: Mostly one by one. Between my last 2 tanks, the only changes were the rear panel of the undertray and driving slower. I can't remember what my figures were with the front panel only, then with the middle panels. I didn't record those, since I forgot to write down the odometer reading/needle position/how much gas when I filled up.

[Frank Lee]

That Hermie is unrelentless!

[stonebreaker]

Well, my suggestion would be to take your last mod back off and see what happens.

And I don't really have much first-hand aero knowledge so take this for what it's worth, but it looks to me like the front undertray guides air under the car, rather than around it, and since you don't have a full belly pan, it looks like the lip of the rear pan would catch the air going under the car.

Instead, might I suggest a front air dam like this (although maybe not QUITE so radical):




The Car
A full bodied 1996 Impala SS that has been in the wind tunnel for
aero mods. Improved the Cd from .320 (stock) to .256
The Engine
A naturally aspirated fuel injected 572 CI Dart big block. 700 RWHP
The Future
Setting a record at Bonneville. There is an existing class record at
241 MPH / 387 KMH. This is a blown gas record that the GIANT SS
could run against. With turbo charging (12 lbs. boost) we can
reach 250 MPH / 402 KMH.

Here's a pic before he took it to the wind tunnel:


I've spoken with John (the owner of the car) in person a couple of times when he brought it to St Louis for the National club meet.

[AeroModder]

Thanks for the info. I've been rolling an idea for an air dam around in my head for a while, but I haven't gotten to the point of building it. From what I've read, an air dam/undertray combination is more effective than either one alone, correct?