rear diffuser build thread

[winkosmosis]

Originally Posted by binarycortex

I was under the impression that diffusers created extra downforce (Formula 1) which is bad for FE. Any Thoughts?

Downforce itself isn't bad for fuel economy.

A diffuser is like a kamm back for the underside of the car. A kamm back creates lift, a diffuser creates downforce, and both reduce drag

[LeanBurninating]

ya so down force created by generating drag is bad for FE but down force created by reducing drag.. is just reducing drag as far as FE is concerned. Right?

Thanks for the input guys, still no takers on the angles, huh?

[aerohead]

All the info you need is in the stickys and seminars.You'll be able to go it alone.

[jonEmetro]

I think a diffuser will help reduce drag. The air going over the car is high velocity/low pressure and the air going under is low velocity/high pressure. Thats what creates lift, and therefore, drag. If you can reduce that pressure differential by increasing the velocity of the air going under the car you should reduce drag.

[MetroMPG]

FYI, here's the info on undertrays Phil contributed:
http://ecomodder.com/forum/showthrea...html#post29811

For what it's worth, I've never seen a low-drag vehicle with a "finned" undertray - they're just smooth. The fins are something I've only ever seen on racing vehicles (or wannabe racing vehicles). That may be significant. Something to think about.

[MetroMPG]

Another thought: start with a flat, slightly upward angled undertray. Tuft test it. Tufts are your friends. (Use a remote camera to record the results.)

If you find that there's attached flow on your undertray, you can study the direction of the tufts to discover flow direction. If you put a "fin" at any other angle than the direction indicated by the tufts, you'll probably be increasing drag through vortex formation off the fin(s).

[wdb]

Originally Posted by MetroMPG

For what it's worth, I've never seen a low-drag vehicle with a "finned" undertray - they're just smooth. The fins are something I've only ever seen on racing vehicles (or wannabe racing vehicles). That may be significant. Something to think about.

This is a bit elementary looking but it is nevertheless very instructive. According to them diffusers, particularly rear diffusers, and major players in the aero game:

Superhachi.com - Downforce Basics

To quote that page:
"The most effective diffusers are closed on the sides by walls that extend close to the ground, in effect forming a sealed tunnel (sometimes referred to as a "ground effect tunnel") only open at the ends. Because air cannot come in from the sides, it is forced to accelerate through the entrance of the diffuser to fill it. This acceleration decreases the pressure of the air at the inlet of the diffuser creating downforce. "

[FastPlastic]

Originally Posted by LeanBurninating

I was actually going to go a little cheaper than carbon fiber... haha. I was just going get some abs plastic sheets cut and use one sheet as the belly pan piece and chemically "weld" the fins on like a t joint style. So just five pieces together and screw it into the bottom of the trunk. I think it will end up being about $120 to make if I buy thicker plastic and get it custom cut at TAP plastic. I don't have a table saw....

Ahh, TAP plastics, I know them well. They do good/fast work, pretty darn cheap too. Good choice

[nwbabybronco]

Food for thought:

Special Projects Motorsports

^^^^OFFICIAL POST YOUR REAR DIFFUSER THREAD^^^^ - Honda-Tech

NSX > EPP > Underbody Diffusers & Rear Valences

Official "booty" thread...your rear-end...exhaust & diffuser photo - LotusTalk - The Lotus Cars Community

MX5Nutz > Rear Diffuser?

[vtec-e]

The last post in the mx5 forum is interesting:"You need a maximum ground clearnace of 75mm to achieve any effect. "
Shock horror!! Are they talking about top end speed? I'd hate to go to all the bother and get little or no FE benefit!

ollie