Underbody Tray Design

[Bunger]

So I was thinking about my tray designs today at work, and I figure I'll do it in 3 parts; front, middle and rear. I'll start with the rear, as I think it may yield the best results. I basically keeped the same line as the top of the car just flipped it upside-down. Input?

[Bunger]

Ohh, and I plan to cut holes, or slots rather, in the rear bumper to "vent" the tray. It should be in the black part of the cover so it wouldn't be terribly visible.

[Matt Timion]

Looks good... looks a lot what what I want to do. You realize you could probably sell undertrays to racers and fuel economy guys alike.

[Compaq888]

or make me a quality one. I have one but I took it off because of design flaws. I can't really do much with a dremel, drill and a screwdriver.

[krousdb]

Originally Posted by Bunger

So I was thinking about my tray designs today at work, and I figure I'll do it in 3 parts; front, middle and rear. I'll start with the rear, as I think it may yield the best results. I basically keeped the same line as the top of the car just flipped it upside-down. Input?

You can sign me up for one. What will you make it out of? You will have cutouts for the muffler? Will there be any interference with the rear suspension?

[Bunger]

I have a very large roll of fiberglass, so I was planning to make it from that. I am going to order up some Dzus fasteners to attach it to the underbody and there will be provisions for exhaust outlet, muffler and of course the rear suspension. I may use a piece of thin sheet metal to begin the design and create a mold from.

[MetroMPG]

that's an interesting idea. certainly the right concept - tapering the underbody up towards the rear. if i'm not mistaken, the insight does this (without the bumper holes). mimicking insight aero techniques on a crx would never be a bad idea.

but i have no idea whether it's better or worse to taper to the bottom pan to meet the bottom lip of the bumper ( = potentially larger wake but cleaner flow separation), or tucking it up higher and then cutting holes in the back of the bumper.

the best aerodynamic solution would be to cut a higher lip in the bumper. whether the holes help will probably depend on how many and how large you make them.

i believe expelling air into the rear wake area was done on the ford probe v concept. they did it with "used" air from the cooling system (mid-engine layout, so easier to arrange).

[Bunger]

Well I crawled under the car today and took a bunch of careful measurements. I've gone and made an image that protrays my car at its current ride height and the new design of the underbody tray.

MetroMPG, before I had even gotten to read your post, I had come to a similar conclusion about the rear bumper. After looking at the amount of space under the car, the new design is the only real practical solution, as the previous one would require that I cut out the spare tire well.

Here is version 1.50:



Sorry its a little big, but its 1/5 the size of the image I was working on. Within 1-2% this imagine is scaled to 1 pixel = 5mm.

[SVOboy]

Ah, d00d, totally kewl.

What do you think will have to be done with venting the engine if a full tray goes on? Prop up the hood a little bit?

This is a very neat idea, Matt, can you post the links to the full CRX undertray you showed me before?

[Bunger]

As far as venting the engine bay, I had thought about raising the rear of the hood to allow venting over the cowl. This may also help with drag over the wiper arms (if I put them back on... the motor is out too... PITA).

I'd love to see some pictures of a CRX underbody tray! Is it the land speed record CRX in Aussie?