I saw this posting on EBay and was curious if anyone has installed one, or has any experience as towards whether they're effective or just bling:

http://cgi.ebay.com/ebaymotors/ws/eBayISAP...33646#LARGEVIEW

 

Btw, I remember seeing a real Feels diffuser for around $600 - $700. If you really want one check out bulletproof.com or rmstuning.com.

 

I'd get one if there's any real benefit besides looking cool. It seems like nobody has one, the one's the have one don't read this site and/or want to comment on it, or they are all bling. I have posted this question a couple of times and no one answers with any info.

Rear diffusers are coming out on Ferrari's and Alfa's, but I wonder what effect if any these aftermarket ones have? I'd think the fins would have to be pretty close to the ground to be effective.

 

I don't know much about them, but my understanding is that they dissipate the hot air under the car, hence reducing lift(improving downforce). For the most part front spoilers, rear spoilers, and diffusers all work optimally at higher speeds... So I assume it would be functional at 100 plus mph, and otherwise for bling. Of course this is all speculation, I don't really know anything.

 

They do help areodynamics. Look at the bottom of your car- now imagine if the top was like that? The car would have a terrible cod. Smooting out the bottom will give you a higher top speed and faster high end acceleration.

 

That thing shown in the picture is not likely to have any benefit. There is a lot more to good aerodynamic design than just making something that kind of looks like something else.

-Mike (aeronautical engineer)

 

I wouldn't think the item pictured would do anything, but you do see rear difussers on DTM type cars, so, on the extreme they do work. I'd much rather have the car pulled to the ground from the bottom than pushed down from the top.

I am going with the all bling opinion until someone can show different.

I wish someone who has one would care to join in...

Here's an explanation: http://www.insideracingtechnology.co...0underwing.htm

 

No, I don't think you do. Both ways produce downforce, both ways produce drag. Pushed down from the top (assuming a wing) is a lot easier to adjust. And most crucially, it doesn't change as much when your ride height changes (due to a bump, for instance).

A nice smooth underside that is low in the front and comes up in the back will produce some good downforce (and a lot of drag). But just tacking this thing on to the back where the airflow is already dirty will probably do nothing good, and may in fact make the car more unstable at speed. Only way to know for sure, though, is to test it (either in the real world or in CFD). My money says these manufacturers don't know CFD from BFDs.

 

From an aesthetic perspective

 

I think this diffuser will work just as well as the one produced by Feels or any other company. Producing downforce by smoothing the under car flow and increasing its velocity pretty simple and easy to do. By simply creating a complete under car tray that is relatively flat will decrease lift at speed.

And downforce created by a venturi (diffuser) has much less drag than downforce created by flow deflection (wing or spoiler). This is why cars such as the Modena, the Enzo and the McLaren F1 utilize diffusers instead of large drag producing wings.

Don't be fooled by the thought that you have to spend big money to get the great performance that the more high priced companies sell. Burt Rutan proved that just a couple of weeks ago.

-Ben (Civil Engineer specializing in Hydraulics)