[Dark Silver S]

Has anyone seen a rear diffuser tray that actually works? It would be nice to have a functioning tray that actually helped with downforce AND eliminated the vortex that puts glop on the boot. It might be as simple as attaching a underbody cover from the rear seating area to the bumper.

Any thoughts?

(See this from the Audi R8 for a reasonably good view of a diffuser.)

[Mugami]

You need to ask SMG. He has the Harman rear disfussor. But you wont get the type of downforce you see in you pic from a bolt on. The car you have there just like F1 cars ahve a smooth underbelly forcing the air go go as faster under the car than above then allowing for the expansion just before the rear of the car will cause an extreme vacume and downforce. IF you seen those cars run in the rain you know those cars create one heck of a rooster tail from the rear and i dont mean the tires. So the rear ends get quite dirty.

Possible solutions: Ive seen a Mid wing made for the mini this may stop the glop from hitting the back window.
Also try running a 3-4" extended plate from the top of the bottom molding(just above the exhaust) Neither is appealing to my eyes but may help on keeping the glop to a minimum.

[SMG]

i'd say the front spoiler is more effective then the rear diffuser when entering a corner in high speed....i think the most important thing is to have a nicely setup suspension best suits your driving style.....hope it helps.

[Dark Silver S]

Thanks for the replies. I wasn't looking for LeMans downforce, I know there are too many other cluttering things underneath (although I must confess I've always wanted to try a full underbody panel - it's a bit difficult with front engine/rear drive).

My main intent was to keep the back end clean without totally upsetting 70+ handling. On a previous vehicle, I tried big mudflaps (18" wide, and hanging all the way to the gound), and that didn't do anything for keeping the back clean. The mid-wing might work, but it would be a certain parking casualty.

Mugami, I know that F1 and LeMans prototypes have enough aero to totally vacuum the road. While I think that should be done on most of the roads I use, I'm not willing to be the one to do it.

[Mugami]

understood ScooperS. on my second idea im not talking like mudflaps im talking about a 3-4" horzanal sheet across the rear not vertical mudflaps. The dirt that gets on the back of the car isnt kicked up from the tires but sucked up from the road behind the car. If I remember some of the Bronco 2 along with other trucks used a wing just above the rear glass pointed straight down to keep the window clean and not to help the truck grip better.

[Damo]

I don't think it so much dirt being flung up from the road but also from everwhere else. Because the back of the Car is almost flat as you travel it creates a vacuum as you get faster so dirt from all directions gets sucked onto the rear of the car.

[Dark Silver S]

Quote:

Originally posted by Mugami
... im talking about a 3-4" horzanal sheet across the rear not vertical mudflaps.

Yes, I know you weren't talking about mudflaps - I was just saying that I tried them before, and they don't do the job.

Where would you place this horizontal wing? Top, bottom, mid-hatch? Would 4" extend back beyond the bumper (and get smucked by poor parkers)?

Short of a tear-drop fairing (or a Kamm fairing), we may have to live with this problem. IIRC, even prototypes are dirty on the back after a race.

This may be a question for the aero-engineers with wind-tunnels.

[scott_roberts]

Dark Silver S,

I agree. I'm in need of an affordable diffuser, and more importantly, one that works. I have heard the Hamann rear diffuser does not work with a lowered car . . . so that option is gone. How about the rear diffuser on the Mini S3 that races in the Belcar series? Check it out here: http://groups.msn.com/mini2003/spabe...to&PhotoID=124

Now that's the diffuser I want!!!

[pocketrocketowner]

For diffusers to work they need tunnels in front of them for at least 60% of the wheelbase.
When race sanctioning bodies want to negate a high downforce chasis's advantage over flat bottomed cars they restrict the length of the shaped underneath (diffuser) to something like 45% of the size of the wheelbase or force them to start them at the rear axle plane and go back.

All this to suggest that a diffuser on a MINI or any production car may be cool looking but the chances of it actually having any kind of effect are pretty close to zip......

[twouptons]

Quote: Originally Posted by Mugami

If I remember some of the Bronco 2 along with other trucks used a wing just above the rear glass pointed straight down to keep the window clean and not to help the truck grip better.

This was very popular on station wagons (estates...) from the 1970s-80s since it's a fair bit cheaper than wipers. They are also still used on minivans and SUVs - essentially cars that are heavy in the rear and not asked to do much in the way of aggresive driving.

The downside is that they produce lift (and drag if they're just tacked on willy-nilly), which will adversely effect high-speed handling.

A book I read a year or so ago suggested they're only effective for about the top third of the rear surface - good for the window, but the rear of the car will still get dirty, so washing frequency won't be reduced...

-Eric