I want my Fiero to have an air diffuser. Instead of building one completely from scratch, I instead decided to mold one into the rear fascia. My design is somewhat similar to the Ferrari F60, which has two venturi tunnels, one on either side of the license plate. Here's a photo of the Ferrari from which I received the inspiration:



And here is my concept sketch:



In order to mold in the air diffuser, I first had to chop out some of the fascia. Actually, I chopped out most of the bottom, leaving only the ground effects on the sides. Below are photos before and after the chop.





I then mounted the chopped fascia back onto the car to take some measurements. The measurements will help to determine the dimensions of the diffuser, and likewise the fiberglass mold.

Speaking of fiberglass molds, I had to build one. I decided to go the cheap-n-sleazy route, using scrap wood and styrofoam. The mold has 3 pieces, the center piece for the license plate area, and the two sides which comprise the venturi tunnels. The tunnels not only expand sideways, but also upward. Below is a shot of the wood frame.



I filled the frame with styrofoam, and cut it with a hot wire. Below, you see the styrofoam before and after cutting. BTW, this is the center section of the mold.





Unfortunately, my hot wire cutting skills were a bit lacking. So I had to smooth things out with some putty. After I got a halfway-decent surface finish, I used spray glue to attach garbage bag plastic to it. The fiberglass resin won't bond to garbage bag plastic. I told you it was cheap-n-sleazy!

quote Originally posted by Blacktree: *snip* Unfortunately, my hot wire cutting skills were a bit lacking. So I had to smooth things out with some putty. After I got a halfway-decent surface finish, I used spray glue to attach garbage bag plastic to it. The fiberglass resin won't bond to garbage bag plastic. I told you it was cheap-n-sleazy!

What did you use to heat the wire? Or did you rig up something electric to do it? Ive been wanting to carve some foam and using hobby knives just dont cut it .. ( err.. sorry about the potential pun there )

Very interesting, can't wait to see how this progresses.

Looks good so far.

User00013170: I bought some heater element wire off ebay and hooked it up to a 12Volt DC power supply. I can't remember how many Ohms per foot it's rated for. But I remember that it's Nichrome wire. And my foam cutter has about 2 feet of wire. The wire gets just hot enough to melt the styrofoam, but not hot enough to burn it.

Hmm... maybe I should write a "hot wire foam cutter" build-up?

quote Originally posted by Blacktree: User00013170: I bought some heater element wire off ebay and hooked it up to a 12Volt DC power supply. I can't remember how many Ohms per foot it's rated for. But I remember that it's Nichrome wire. And my foam cutter has about 2 feet of wire. The wire gets just hot enough to melt the styrofoam, but not hot enough to burn it. Hmm... maybe I should write a "hot wire foam cutter" build-up?

I was going to try that same thing next ( using a wood form to hold the wire ), but didnt know if there was another idea i hadnt thought of . tks

looks real good!

im assuming you will be taking a mold from the whole thing once its done? glass and urethane arent the kind of friends that stick together..

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You can get the Nichrome wire from hobby stores that sell RC airplane supplies. We use it all the time to cut wings etc.

I use a harp made from 1/2 elect. conduet to support the wire since often cut 3-4 ft wings sections.

It really helps if you have a 3-4 amp variable power supply to adjust the voltage. You want it hot but not enough to make the wire glow.

I also use it to cut the foam board to insulate my basements walls. You can shape the panels to fit around outlets etc. without having little styro bits all over the place.

guitar string and a nintendo power supply works too...

looks like a decent attempt. keeping it in the mental file.

I like it; should look good once you're wrapped up Curious what you're planning on using for the fins?

Steve

I love the idea here, but I'm afraid I may be missing something. What do you plan to do with the exhaust? In it's stock location wouldn't it be right in the middle of your diffuser rendering it useless from an aerodynamic (and by some counts, asthetic) standpoint? I'm sure you could reroute the exhause to exit somewhere else on the fascia, but I don't see where you've left much room for it.

More PICTURES.

Looks sweet.

John

side exhausts from a truck would look sick!!! the ones that go through the truck bed and have a dual outlet

I like that. That is so creative.

First of all, thanks for the comments.

Second of all, I have a custom exhaust that should work well with the diffuser setup. More on that later.

Sweet!

Now you need to do this for the rest:

Awesome, man. Check this out if you haven't seen it:

http://www.kimini.com/Diaries/2004Early/ The guy starts building his own diffuser around Jan. 25.

quote Originally posted by Blacktree: First of all, thanks for the comments. Second of all, I have a custom exhaust that should work well with the diffuser setup. More on that later.

I'll be waiting

maybe when this is done you could try something with the front of the car to use what steven snyder has on his to help with the downforce of the car or lack of it at high speeds....I have done a little checking and there will need to be a lot of modification done to the car to get it all to work right. but if that is POSSIBLE then triple digit speeds shouldn't be a worry for anyone anymore!!! didn't mean to thread jack by any means.

A hood vent makes a world of difference for the front.

I also have a vastly redesigned front compartment which makes blocking off the bottom like I did more feasible. I seem to have a high speed high load cooling issue periodically now though. It may or may not be related, since I had the engine out and made some modifications a little while after I added the tray.

With the rear diffuser and a good hood vent the downforce should be greatly improved. I will continue looking for ways to reduce upforce at the front.

I already did some work on the front. Now I'm tweaking the back to match.



You can read about that here.

COOL

[This message has been edited by goatnipples2002 (edited 10-21-2006).]

I'm not really sure what you mean. I designed the diffuser so that the fins will divide the diffuser sections almost exactly in half.

I like what you did to the front too.

nvr mind

[This message has been edited by goatnipples2002 (edited 10-11-2006).]

The exhaust tunnels weren't big enough for me. I want this thing to be somewhat functional.

quote Originally posted by Blacktree: Now I'm starting to build the fins. They'll be built from a wood core (1/4" thick poplar) encased in fiberglass. The mounting flanges will be molded into the fins. Here are the wood cores for the fins: The bottom (darker) one still needs to be sanded smooth.

Just curious blacktree, you mentioned the fins being incased in fiberglass,..is that just for the plug or for the actual part ?

I thought it was good to avoid using wood in the actual part as it expands and contracts and could cause future problems. Is this correct or am i mis-informed.

I really have no clue so i am just asking.

Thanks

Tony

Tony I think that wood will only expand and contract if exposed to the moisture. otherwise I would think that they would expand at the same rate..

FYI- a diffuser won't work without a flat underbody panel to kill any upstream turbulence...

It would be like putting flaps on a log. Yeah, it might gain you a little lift, but nothing compared to putting flaps on a wing.

quote Originally posted by ryan.hess: FYI- a diffuser won't work without a flat underbody panel to kill any upstream turbulence... It would be like putting flaps on a log. Yeah, it might gain you a little lift, but nothing compared to putting flaps on a wing.

So it will/could be beneficial but no as effective w/o a belly pan?

quote Originally posted by Blacktree: The exhaust tunnels weren't big enough for me. I want this thing to be somewhat functional.

[This message has been edited by goatnipples2002 (edited 10-21-2006).]

quote Originally posted by Steven Snyder: Sweet! Now you need to do this for the rest:

Could you share a little bit on your flat underbody panel?

I looks like aluminum to me, but for safety it should be made of something softer. (to allow breaking under an accident without grabing or dragin anything). Just as a note, Ferraris under-panels are made off very cheap fiberglass.

JG

pretty sure he bought sheet ABS plastic for that

To get maximum effect, the diffuser should be incorporated into the tail end of a belly pan. But even without a belly pan, it can still generate some downforce. It just needs to have some "unspoiled" airflow across it. Unfortunately, my diffuser has the engine cradle and rear suspension mucking up the airflow. And there's no belly pan. So its effectiveness in that regard will be greatly reduced. To compensate for that, I decided to make it as big as possible.

For the most part, it's just a big air vent that happens to look like a diffuser. I'm hoping the extra vent area will help extract air from under the car. And maybe the venturi shape will create a little downforce. Plus it looks cool.

BTW, I made some progress today. I did some filling and sanding, and more work on the fins. I laid up some fiberglass for the mounting flanges on the fins, and set the fins in place on that. The epoxy will bond to the wood as it cures. I laid the fiberglass onto the diffuser itself, so the contours will match. The diffuser and the fresh fiberglass are seperated by a layer of duct tape. And I rigged up a fin holding device using some scrap wood, to keep the fins in place until the epoxy cures. See photo below.



Here's a close-up of the fin sitting on the fresh fiberglass, with the fin holder.



FUN FUN!!!

[This message has been edited by Blacktree (edited 10-12-2006).]

I love it. Quick question, how does a rear diffuser create downforce. I want to go spoilerless, and that sounds cool.

What is an air diffuser? Read this.

Oh. Is there any particular way to set one up? Like a spoiler? Different angles?